DE10206076A1 - Transmission of multimedia data streams for media-on-demand system, by forming sub-group of data units from data units in two data streams and transmitting during transition time - Google Patents

Abstract

The method involves transmitting a data stream via multiple transmission channels, starting at a time t1s. The stream comprises multiple data units. A further data stream is transmitted via at least some of the transmission channels at a start time t2s. During a transition time, starting at time t2s, a sub-group of data units is formed from some of the data units and transmitted to a receiver.

Description

1 Introduction

Television has become an integral part of the past 50 years of everyday life. With the availability of digital technology for recording, The transmission and playback of video information is becoming more and more flexible developed for the consumer ("Pay-per-View", "Pay-TV", "Video-on-Demand" etc.), in order to pay for customers by paying more attention to their needs To win program providers or program offers. There is also individualization of the offer of importance: ideally the customer should have his personal Satisfy program requests.

• - wann mit dem Betrachten eines Programms begonnen werden kann,
• - die Möglichkeit, eine oder mehrere Pausen während des Programms einzulegen und es trotzdem vollständig (also ohne Informationsverlust) betrachten zu können,
• - eine große Anzahl von Programmen zur Auswahl zu haben.

The following properties are relevant from a user perspective (viewer):

• - when you can start watching a program,
• - the possibility to take one or more breaks during the program and still be able to view it completely (i.e. without loss of information),
• - have a large number of programs to choose from.

Typical functions of a video recorder - such as the ability to fast forward or rewind, Image search and slow motion, however, are of secondary importance.

It should also be noted that this text primarily speaks of "(video) films" becomes. This is only an example. Likewise, radio programs can also Multimedia presentations can be transmitted according to the schemes described.

The essential technical parameters are the necessary transmission bandwidth, the required reception bandwidth and the storage space on the reception systems.

A number of technologies have been developed over time that are increasing for an user-friendly program offer should provide. These are discussed in the following section briefly outlined.

The system overview shown in FIG. 0 is generally taken as the basis, since in principle all processes are based on such an architecture (albeit in a modified form). A transmission system consists of a PC or a special computer for reading, preparing and sending programs and one or more transmission stations for the physical transmission of the programs via the respective or the respective communication media. The transmitting station can be, for example, a satellite uplink, a cable head station, an ISDN, PSTN, or ATM router, a mobile radio or WLAN base station or just a network adapter for a local network (Ethernet, WLAN, etc.).

The broadcasting system uses a number of digitally stored programs. The Programs can be on tape, hard drive, RAID system, DVD or other media; they can be kept locally at the sending system (e.g. on a hard disk in a PC), on other locally neighboring systems (e.g. on one via a computer network accessible mass storage) or kept geographically separate and via a Computer network (cable, satellite, Internet, etc.) can be accessed. The programs can be in one or multiple quality levels, they can be in one or more files on one or be kept on several data carriers.

The transmission systems read them at a certain point in time (in accordance with the requirements of data to be sent before or to this Time locally or over a network and transmit it over one or more Communication media to the 0 to n recipients.

The receivers receive the programs via the communication medium and prepare them according to their content (audio, video, data, files, text, multimedia, etc.) and - if desired by the (human) "viewer" - present them in a suitable form (Playback via loudspeaker, display on the screen, stimulation tactile Output devices, etc.). A variety of devices can be used individually or in combination Form receiver. These include, for example, PCs (e.g. with a monitor and / or loudspeaker), Set-top boxes, digital televisions, analog televisions in combination with digital ones Receiving devices such as a PC or set-top box, (digital) video recorders, digital radios, analog radios in combination with digital receivers etc.

A return channel can optionally be formed between a receiver and the transmitter, who can use one or more (similar or different) communication networks (the from the transmission networks for the programs may be different). About one such a return channel, the receiver can a transmitter z. B. tell what programs he when wants to receive, whether he is currently receiving a program (and possibly which one), which Program parts of a program he has already received, the quality of reception, etc.

2. State of the art

• a) Klassisches Fernsehen: ein Programm wird einmalig zu einer vorgegebenen Sendezeit auf genau einem Kanal ausgestrahlt. Zuschauer können dieses Programm nur zu genau diesem einen Zeitpunkt betrachten. Pausiert der Zuschauer kurz, so gehen ihm Informationen im Programm verloren.
• b) Zyklische Wiederholung eines Programmteils: ein Programm wird in einem Kanal nach seinem Ende wieder von Neuem ausgestrahlt, ohne daß es dabei zu Überlappungen kommt. Ein Zwei-Stunden-Spielfilm würde auf diese Weise alle zwei Stunden von Neuem gesendet. Zuschauer können den Film jeweils zu Beginn eines solchen Abschnitts von Beginn an betrachten, müssen also ggf. eine recht lange Wartezeit in Kauf nehmen. Will der Zuschauer pausieren aber nichts versäumen, so muß er im folgenden Abschnitt (z. B. 2 Stunden später) mit dem Betrachten fortfahren.
• c) Überlappendes Aussenden eines Programms ("Near Video-on-Demand", auch als Staggered Broadcasting bezeichnet): ein Programm wird auf mehreren Kanälen überlappend ausgestrahlt. So beginnt ein Zwei-Stunden-Film etwa auf vier Kanäle verteilt alle 30 Minuten von neuem. Die Wartezeit bis zum Beginn eines Films sinkt, ebenso sinkt die Wartezeit bei einer Pause ohne Informationsverlust. Dafür steigt die erforderliche Bandbreite. Dieses Verfahren entspricht dem Versenden auf den Kanälen 1 bis 4 wie in Fig. 6 oben beispielhaft dargestellt.
• d) Video-on-Demand: ein Programm wird auf Anfrage eines Benutzers gezielt an diesen ausgesendet. Der Benutzer ist in optional in der Lage, die Programmwiedergabe zu steuern, also beispielsweise Pausen einzulegen. Hiermit werden die Kundenbedürfnisse bezüglich eines Programms optimal befriedigt; allerdings hat sich dieses Verfahren als nicht praktikabel erwiesen, insbesondere weil die notwendige Übertragungsbandbreite proportional mit der Anzahl der Empfänger steigt. Daher wurden alternativen Ansätze verfolgt, wie im folgenden kurz dargestellt.
• e) Zwei Gruppen von Verfahren werden eingesetzt, um Broadcasting bzw. Multicasting statt individueller Informationsverteilung einzusetzen, um Video-on-Demand zu realisieren: verschiedene Varianten von Pyramid Broadcasting (mit meist unterschiedlich großen Informationseinheiten) und Varianten von Harmonic Broadcasting (wie auch in der Anmeldung DE 100 08 949.6 beschrieben) mit i. d. R. gleich großen Informationseinheiten. Diese Verfahren reduzieren die erforderliche Bandbreite für die Übertragung eines Video-on-Demand-Programms auf eine Größe, die nur von der Dauer des Programms und der Granularität der Einstiegszeitpunkte abhängt, nicht aber von der Anzahl der Empfänger. Diese Verringerung der Übertragungskapazität wird durch Zwischenspeichern von Programmteilen erkauft, die nach einem fest vorgegebenen oder dynamisch durch den Sender berechneten Muster übermittelt werden.
• f) Erweiterungen hierzu (wie beispielsweise in der Patentanmeldung DE 100 08 949.6 beschrieben) sehen vor, daß Rückkopplungen mit den Empfangssystemen den/die Sender darüber informieren, wann welche Programme betrachtet werden, so daß sich hier weitere Optimierungen realisieren lassen. Gibt es beispielsweise keinen Betrachter für ein bestimmtes Programm, so muß hiervon gar nichts übertragen werden. Ebenso kann das Übertragungsmuster genau an die Anforderungen der Betrachter angepaßt werden.
• g) Schließlich wurde als Erweiterung vorgeschlagen, die Verfahren (c) und (e) zu kombinieren, um einfache Geräte, die über keinerlei oder nur wenig lokalen Speichern zum Zwischenspeichern von Informationen verfügen gleichzeitig mit leistungsfähigen Systemen bedienen zu können. Hierbei werden k Videoströme im Staggered Broadcasting-Verfahren gesendet, l weitere werden dazu verwendet, jeweils einen Teil (den Anfang des Programms) der entsprechend (e) zu übertragen, um damit die Wartezeit eines Empfängers zu reduzieren. Diese Idee ist in Fig. 6 bespielhaft veranschaulicht.

A number of methods for transmitting media streams by broadcast are known at the present time. These include, among others

• a) Classic television: a program is broadcast once on a specific channel at a specified broadcast time. Viewers can only view this program at exactly this one time. If the viewer pauses briefly, information in the program is lost.
• b) Cyclic repetition of a program section: a program is broadcast again in a channel after its end without overlapping. A two-hour feature film would be broadcast again every two hours this way. Viewers can watch the film from the start at the beginning of such a section, so they may have to put up with a long wait. If the viewer does not want to miss anything, he must continue viewing in the following section (e.g. 2 hours later).
• c) Overlapping broadcasting of a program ("near video-on-demand", also known as staggered broadcasting): a program is broadcast overlapping on several channels. A two-hour film, for example, begins again every four minutes on four channels. The waiting time until the beginning of a film is reduced, as is the waiting time for a break without loss of information. The bandwidth required for this increases. This method corresponds to the transmission on channels 1 to 4 as exemplified in FIG. 6 above.
• d) Video-on-Demand: a program is specifically sent to a user at his request. The user is optionally able to control the program playback, for example taking breaks. This optimally satisfies customer needs regarding a program; however, this method has proven to be impractical, particularly because the necessary transmission bandwidth increases proportionally with the number of receivers. Alternative approaches were therefore pursued, as briefly outlined below.
• e) Two groups of methods are used to use broadcasting or multicasting instead of individual information distribution to realize video-on-demand: different variants of pyramid broadcasting (with mostly different sized information units) and variants of harmonic broadcasting (as in the Application DE 100 08 949.6 described) with information units of generally the same size. These methods reduce the bandwidth required for the transmission of a video-on-demand program to a size that only depends on the duration of the program and the granularity of the entry times, but not on the number of recipients. This reduction in transmission capacity is purchased by temporarily storing program parts that are transmitted according to a predefined or dynamically calculated pattern by the transmitter.
• f) Extensions to this (as described, for example, in patent application DE 100 08 949.6) provide that feedback with the receiving systems inform the transmitter (s) when which programs are being viewed, so that further optimizations can be implemented here. For example, if there is no viewer for a particular program, nothing needs to be transmitted. The transmission pattern can also be adapted precisely to the requirements of the viewer.
• g) Finally, as an extension, it was proposed to combine methods (c) and (e) in order to be able to use simple systems with little or no local storage for temporarily storing information with powerful systems. Here, k video streams are sent using the staggered broadcasting method, l others are used to transmit a part (the beginning of the program) according to (e) in order to reduce the waiting time of a receiver. This idea is exemplified in FIG. 6.

• a) Videorekorder ermöglichen das Aufnehmen ("Speichern") des nach (a)-(g) ausgestrahlten Programms zu den jeweils möglichen Zeitpunkten. Benutzer können den Programminhalt dann später betrachten. Im Falle eines Videorekorders, der nur sequentiell zugreifbaren Medien (z. B. ein Band) zur Speicherung des Videofilms verwendet, kann die Betrachtung des Films erst nach Beendigung der Aufnahme beginnen (und im Falle eines einzelnen Gerätes i. d. R. nicht parallel zu einer weiteren Aufnahme).
• b) Digitale Videorekorder ermöglichen das (optional benutzergesteuerte) Voraufzeichnungen von Spielfilmen innerhalb eines Zeitraum (z. B. eines Tages) und halten diese Spielfilme dann auf einem digitalen Speichermedium (z. B. einer Festplatte) vor. Der Benutzer kann bei Bedarf Filme von der Festplatte zu einem von ihm frei wählbaren Zeitpunkt abspielen; hierbei sind Unterbrechnungen des Betrachtens ebenso wie Vor- und Zurückspulen, wiederholtes Betrachten usw. möglich.
• c) Zur Optimierung der Verfahren (e) und (f) wurde vorgeschlagen, einen Teil (typischerweise den Anfang) des Programms (nicht aber das ganze Programm wie in ii.) vorab als Datei zu übertragen (siehe auch die europäische Anmeldung EP 01 100 521.2). Bereits mit geringer Vorabübertragung (z. B. weniger als fünf Minuten eines Zwei-Stunden-Programms) kann die erforderliche Bandbreite des Verfahrens nach (e) deutlich reduziert werden.

Methods for automatically pre-storing parts of this information stock are also known:

• a) Video recorders enable the recording ("saving") of the program broadcast according to (a) - (g) at the respective possible times. Users can then view the program content later. In the case of a video recorder that only uses sequentially accessible media (e.g. a tape) to store the video, the film can only be viewed after the end of the recording (and in the case of a single device usually not parallel to another Admission).
• b) Digital video recorders enable the (optionally user-controlled) pre-recordings of feature films within a period of time (e.g. one day) and then keep these feature films on a digital storage medium (e.g. a hard disk). If necessary, the user can play films from the hard disk at a time freely selectable by him; interruptions of viewing as well as fast forward and rewind, repeated viewing etc. are possible.
• c) To optimize methods (e) and (f), it was proposed to transfer part (typically the beginning) of the program (but not the entire program as in ii.) as a file in advance (see also European application EP 01 100 521.2). Even with a small amount of advance transmission (e.g. less than five minutes of a two-hour program), the required bandwidth of the method according to (e) can be significantly reduced.

• a) Auswechseln eines Films in einem Übertragungskanal bzw. einer Gruppe von Übertragungskanälen: die oben beschriebenen Verfahren sind zunächst für die effiziente Übertragung eines Programms über einen oder mehrere Übertragungskanäle konzipiert. In der Praxis müssen jedoch Programmwechsel durchgeführt werden können, wenn etwa jeder Spielfilm für einen Zeitraum von 10 Stunden angeboten werden soll; danach muß ein fließender Übergang zum Nachfolgefilm ermöglicht werden:
• b) Unterstützung von Live-Medienströmen, also die Übermittlung von Inhalten, die vor Sendebeginn nicht aufgezeichnet und demnach auch nicht vorab verteilt werden können. (Entsprechend muß es auch möglich sein, ein Programm mit einem neu erworbenen Gerät zu betrachten, daß zum Zeitpunkt einer evtl. Vorab-Übertragung noch nicht empfangsbereit war.)
• c) Explizite Berücksichtigung der Parameter der Empfangssysteme (insbesondere des verfügbaren Speicherplatzes) bei der Erstellung eines Sendemusters für ein Programm.
• d) Ermöglichen von Pausen bei Betrachten eines Programms; das bedeutet, dass die Wiedergabe vorübergehend unterbrochen und nach einiger Zeit fortgesetzt wird. Während der Pause werden aber weiterhin Informationen empfangen. (Dies leitet sich im wesentlichen aus den beschriebenen Verfahren ab, jedoch wird zusätzliche Speicherkapazität benötigt, da das Programm nicht kontinuierlich wiedergegeben wird.

The methods outlined above are implemented today in the form described and in various modifications thereof. However, they insufficiently take into account three essential aspects in practical use:

• a) Replacing a film in a transmission channel or a group of transmission channels: the methods described above are initially designed for the efficient transmission of a program via one or more transmission channels. In practice, however, it must be possible to change programs if, for example, each feature film is to be offered for a period of 10 hours; after that, a smooth transition to the follow-up film must be made possible:
• b) Support of live media streams, i.e. the transmission of content that cannot be recorded before the broadcast begins and therefore cannot be distributed in advance. (Accordingly, it must also be possible to view a program with a newly acquired device that was not ready to receive at the time of a possible pre-transmission.)
• c) Explicit consideration of the parameters of the receiving systems (in particular the available storage space) when creating a transmission pattern for a program.
• d) allowing breaks when viewing a program; this means that playback is temporarily interrupted and continues after some time. However, information is still received during the pause. (This is essentially derived from the methods described, but additional storage capacity is required because the program is not played continuously.

This document outlines procedures to solve precisely these problems and thus to make a media-on-demand system practical.

3. Description

First some introductory remarks on terminology in this document. FIG. 1a shows an overview of the terms used. Some other terms are visualized in FIG. 3a.

The subject of consideration is at least one program (e.g. a feature film), the is characterized by a number of parameters. The program has one Program duration T_s (typically measured in seconds). The program can be downloaded in two components are broken down: a pre-distributed portion, which is usually the The beginning of the program contains, with a partial program duration T_v and with a multicast one of the methods described in the introduction, transmitted in real time with a Program duration T_s - T_v. If there is no advance transfer, then T_v = 0, and that entire program is broadcast in real time. The entire program can also be made in advance transferred (e.g. as a file). Then T_v = T_s.

For the transmission - in advance as well as in real time - the program is divided into individual Data units disassembled; to simplify the description it is assumed that the in the Program parts containing data units each have the same duration. The duration of a program part contained in a data unit let Δt. Because the whole program in individual data units is divided, this results in a division of the program into n data units each with a duration of Δt = T_s / n. From the one described above Splitting into previously distributed and real-time transmitted components of the program results taking into account the division into data units that the advance distributed part consists of v = T_v / dt data units and the real-time part consists of n - v = (T_s - T_v) / Δt.

For the transmission of the program, the various data units can be divided into different transmission channels. The same or different, constant or variable bandwidth for data transmission can be assigned to each of these transmission channels. FIG. 1b shows an example in which a channel k, the data units Di (2 ≤ i ^k <2 ^{k + 1)} are transmitted. The bandwidth of each channel is constant in this example, each data unit Di is transmitted depending on its assignment to a channel k with 1/2 ^{k the} bandwidth of the channel - which is realized in the example by only having it every 2 ^k time units Δt is sent.

The transmission of the program is provided from a certain point in time: ti_s for the program i (see also FIG. 3a). From this point onwards, the transmission of data units of the program begins. A viewer can start to receive the data units of the program and reproduce the program from the time ti_s or later. Because of the use of the procedures outlined in Section 2 (e), the viewer need not begin receiving and / or viewing the program at time ti_s; it is sufficient if it "switches on" at a later point in time (the point of entry, see FIG. 1c). If a program is not to be shown permanently from ti_s, but is only to be "received" within a certain period of time - within the broadcasting period T_a - an end time ti_e is defined (with T_a = ti_e - ti_s). The end time indicates the last possible time at which a receiver can start receiving the program in order to still be able to receive and play the complete program. For receivers who start receiving after ti_e, it is not defined which program parts (i.e. which data units) they will still receive and which not. In particular, the beginning reception at the time ti_e + T_late (with T_late> 0) does not mean that the program is received except for the first T_late time units.

3.1 Program transition: from program # 1 to program # 2

The methods described each use a number of channels to transmit the data units of a program. As a rule, more data units are transmitted per time interval Δt during the broadcasting period T_a of the program, so that a transmission bandwidth is obtained which is a multiple of the playback bandwidth of the program. If several programs are to be transmitted in succession on the same channels, a pause between the successive broadcast of two programs must potentially be provided. Viewing program # 1 can only begin until time t1_e, but it blocks the channels until a later time t1_e + T_past (generally T_past ≤ T_s), since data units are still being sent for any viewers that may be present must (see also Fig. 3a). The following describes a method that closes this program gap and enables a program # 2 to follow a program # 1 directly.

In the method described in patent application DE 100 08 949.6, the transmission of a program is started at a time t1_s. It is not necessary to send all data units of the program from time t1_s onwards. As shown in Fig. 2a, the data units need only be sent out step by step so that a (potential) recipient receives the corresponding data unit at the latest at the time of playback: since the earliest possible viewer can only start at time t1_s, a data unit Dx (which contains the content of the program at time tx) are not sent before time t1_s + tx - nevertheless, a broadcast schedule can of course provide this (see also the detailed discussion in patent application DE 100 08 949.6). The data rate to be sent (summed up over the actual use of all available channels) is therefore still low at time t1_s and - depending on the broadcasting plan used - can increase on average until it reaches its average maximum after a program duration, i.e. at time t1_s + T_s thereafter remains constant on average. An example of a mapping to a transmission scheme of data units is shown in FIG. 2b.

A similar observation can also be made if reception (and viewing) of the program is only to be possible up to a certain point in time t1_e. After the point in time t1_e, the beginning parts of the program can then be omitted step by step, so that the required data rate drops. At the latest at the time t1_e + T_past (where T_past ≤ T_s generally applies), no more data units of the program are to be transmitted (cf. FIG. 3a). FIG. 3b shows an embodiment for implementing this method.

As can be seen from these descriptions, the transmission rate increases at the beginning of a Program, decreases at the end of its broadcast. This property can be admitted use suitable times (depending on the selected transmission method) in order to a smooth transition from broadcasting one program # 1 to the next # 2 realize - without additional transmission capacity is required.

As shown schematically in FIG. 4a, the data units to be transmitted less for a program # 1 and the data units to be transmitted more for a program # 2 are mutually equal. FIG. 4b illustrates the example represents an actual schedule, that the position in which data units of the program # 1 to be sent, can be used for successive data units of the program # 2.

The program transition time t2_s = t1_e + Δt must be selected so that the transmission method allows a continuous transmission of all data units of film # 2; this is the only way to ensure that a viewer arriving at time t2_s can also watch film # 2 completely and without interruption. This is shown schematically in Fig. 4a; an exemplary mapping to a concrete transmission scheme is shown in Fig. 4b.

This description also applies analogously if parts of a program are transferred in advance have been. The only requirement is that the data units are transferred in advance for both Programs are selected so that the number of those necessary for real-time transmission Channels (as well as their bandwidth and the division of the data units) are the same (or compatible (The term "compatible" here means that the channels used have enough space for the Program with a larger data volume must offer. When transitioning between two programs Of course, previously used portions of the channel bandwidth can remain unused, as can previously unused portions are filled in after the program change. One is also conceivable Standard program duration (about 120 minutes for a regular feature film), based on which broadcast schedules are created become; real programs may then not make full use of them. Finally, the Differences between two programs in terms of their channel usage when using advance Eliminate transmission completely by appropriately defining T_v.)).

3.2 Transmission of programs without a lead time

• - Der Sender kann den Programmteil nicht vorab übertragen.
• - Der Empfänger kann den Programmteil nicht vorab empfangen.

The procedures presented in Sections 2 (e) and (f) can - as indicated in Section 2 (iii) - be combined with a pre-transmission of parts of the program, such as the beginning of the program. This advance transfer is not possible in various cases, which can be roughly divided into two categories:

• - The broadcaster cannot transmit the program part in advance.
• - The receiver cannot receive the program part in advance.

Conceptually, these two aspects can be reduced to the same basic problem and solve by similar mechanisms. First, the two restrictions presented, then solutions are presented.

3.2.1 Sender cannot transmit the program part in advance

• - Es kann sich um eine Live-Übertragung handeln, so daß die vorab zu übertragenden Programmteile (Inhalte) vorab nicht verfügbar sind.
• - Engpässe im Kommunikationssystem (etwa nicht genügend Übertragungskapazität) können die Übertragung vorhandener Inhalte verhindern ebenso wie
• - Störungen im Zeitraum der Vorab-Übertragung (so daß entweder aufgrund von Rückmeldungen bekannt ist oder vermutet wird, daß nicht alle Empfänger die vorab zu verteilenden Informationen erhalten haben).

If a broadcaster cannot transmit a program in advance, this can have various causes, but will lead to the same result.

• - It can be a live transmission, so that the program parts (content) to be transmitted in advance are not available in advance.
• - Bottlenecks in the communication system (such as insufficient transmission capacity) can prevent the transmission of existing content as well
• - Interruptions in the pre-transmission period (so that either it is known from feedback or it is assumed that not all recipients have received the information to be distributed in advance).

The last two points can naturally also occur in combination. In all three In some cases, the broadcaster is informed that the program parts in question are not with Receivers are present when the real-time transmission begins. While bottlenecks in Communication system or in the event of malfunctions, the information is still available at a later time (but before the broadcasting interval begins) broadcast, this option does not exist for live broadcasting.

This means that broadcasting a live program is the most complex alternative represents, whose solution is also a solution to the other two problem cases. Therefore, in following only referred to the example of the live broadcast.

example Live broadcast

The methods presented as state of the art go implicitly (in some cases this is also the case) explicitly emphasized) assume that the programs to be broadcast at the beginning of the Broadcast duration fully available (for example as a film "conserved"). Only then can in many cases the transmission schedules are fully calculated, only then are all data units available Available from the start, and only then can parts of the program be transferred in advance. This restriction affects all live programs (see definition below). In this Section presents a procedure that allows live programs to be viewed as well transferred like "canned goods".

• - Live-Programme mit begrenzter, vorab bekannter Programmdauer wie etwa Nachrichtensendungen und
• - Live-Programme mit potentiell begrenzter, aber vorab unbekannter Programmdauer wie etwa "Wetten, daß. . .", Sportberichterstattungen usw.

A live program is understood to mean a program that is broadcast live, the contents of which cannot therefore be prepared or distributed in advance. Examples of live programs are news programs such as the "Tagesschau" or "heute", stock exchange and sports reports etc. Live programs can still be divided into two groups:

• - Live programs with a limited, previously known program duration such as news programs and
• - Live programs with a potentially limited but previously unknown program duration, such as "Wetten, dass ...", sports reports, etc.

Here only the first category of live programs (with limited, previously known Program duration).

3.2.2 Receiver cannot receive the program part in advance

• - Der Empfänger kann zum Zeitpunkt der Vorab-Übertragung nicht eingeschaltet sein (z. B. wegen Stromausfall).
• - Der Empfänger kann zum Zeitpunkt der Vorab-Übertragung keine Daten empfangen (z. B. wegen Störung der Empfangsantelle, Schüssel, des Kabels usw.).
• - Der Empfänger ist zum Zeitpunkt der Vorab-Übertragung noch nicht verfügbar, etwa weil das Gerät erst nach Abschluß der Vorab-Übertragung, aber vor Beginn der Ausstrahlungsdauer angeschafft, aufgestellt und/oder eingeschaltet wurde.

There are a number of reasons why receivers cannot receive a part of a program in advance, which are essentially due to (reception-side) unavailability of the communication channel or of the receiver itself:

• - The receiver cannot be switched on at the time of the preliminary transmission (e.g. due to a power failure).
• - The receiver cannot receive any data at the time of the advance transmission (e.g. due to a fault in the receiver, key, cable, etc.).
• - The receiver is not yet available at the time of the pre-transmission, for example because the device was only purchased, set up and / or switched on after the pre-transmission was completed but before the start of the broadcast period.

In all three cases, the viewer can use a real-time Transfer procedure in combination with a pre-transfer the pre-transfer Do not consider the broadcast start of the program.

3.2.3 Approach

Conceptually, it is irrelevant whether a program part before the broadcasting interval begins was not available from the broadcaster (or could not be broadcast for other reasons), or whether the recipient does not receive previously distributed program parts for other reasons could. A common solution for both problem cases is therefore presented here. there is used in the following text without restricting generality (or general Applicability) representative of the problem of the live program defined above.

A live program can be broadcast like a program without pre-transmission (T_v = 0). If a suitable transmission schedule is selected (for example the one shown in FIG. 2b), only the data units known up to then have to be transmitted up to a point in time tx. The individual data units that have already been transmitted are repeatedly transmitted in accordance with the transmission schedule during the broadcasting period. Towards the end of the broadcast period - as also described in 3.1 - the data rate with which data units of the program are sent is gradually reduced to zero.

Since the beginning of the live program (D1,..., Dv) is not known in advance, it can also not be transferred in advance. The advantage of bandwidth reduction therefore cuts through Preliminary broadcast at least at the beginning of the live program.

In order to transmit an output of the daily news of around 15 minutes in length according to the transmission schedule outlined in FIG. 2b, ten times the data rate of a normal television transmission is required without pre-transmission - at Δt = 1 s. If, on the other hand, the first minute (15 Mbytes at a data rate of 2 Mbit / s) were transmitted in advance, the required data rate during real-time transmission can be reduced by 60% to four times that of a normal television transmission.

Should a live program be broadcast over a broadcast period T_a that is exceeds its own length (T_a> T_s), so a large part of the transmission bandwidth used for the transmission of the program start - although this is changed by Transmission would be much more efficient.

• - Die Dateneinheiten D1, . . ., Dv des Programmanfangs werden zunächst regulär nach Sendeplan für eine Echtzeit-Übertragung gesendet (siehe Fig. 5). Diese Dateneinheiten werden aber gleichzeitig so "markiert", daß Empfangssysteme wissen, daß es sich gleichermaßen um eine Vorab-Übetragung des Programmanfangs handelt und diese Dateneinheiten deshalb speichern. (Zu beachten ist, daß diese Markierung implizit sein kann; alle Empfänger können beispielsweise wissen, daß immer die ersten 120 Sekunden eines Programms speichern sollen.) Die einzelnen Dateneinheiten werden ggf. wiederholt gesendet (z. B. in immer größeren Intervallen, wie in Fig. 5 angedeutet, oder indem jede Dateneinheit D1, . . ., Dv jeweils m Mal gemäß Sendeplan übertragen wird), bis schließlich davon ausgegangen werden kann, daß alle Empfänger die vorab zu verteilenden Dateneinheiten erhalten haben. Dann stellt der Sender das Aussenden dieser ein und verfällt in den vorgesehenen Sendeplan einer Echtzeit-Übertragung, die auf vorab übertragene Dateneinheiten zurückgreifen kann.
• - Die Vorab-Übertragung der Dateneinheiten des Programmanfangs kann auch dahingehend abgewandelt werden, daß die Dateneinheiten in einem von der Echtzeit-Übertragung unabhängigen Kanal gesendet werden (etwa als Teil einer Dateidistribution). In diesem Fall wird ein zusätzlicher Kanal (ggf. mit anderer Bandbreite und anderem Übertragungsformat) zur Vorab-Übertragung der Dateneinheiten verwendet). Dies geschieht jedoch im Gegensatz zur reinen Vorab-Übertragung zumindest teilweise parallel zur Echtzeit- Übertragung des Programms.
• - Ebenso kann eine solche Distribution (mit weitaus geringerer Datenrate) im Hintergund permanent aktiv sein, um allen potentiellen Betrachtern den vorab zu verteilenden Programmanfang während der ersten (kurzen) Zeitspanne der Echtzeit-Übertragung zuzustellen. Auch hier wird wiederum ein eigener Datenkanal für die permanente Vorab- Übertragung benötigt.

The invention is the combination of pre-transmission with real-time transmission (which, incidentally, is not only applicable to live programs). It can be implemented in different forms:

• - The data units D1,. , ., Dv of the beginning of the program are initially sent regularly according to the schedule for a real-time transmission (see FIG. 5). At the same time, these data units are "marked" in such a way that receiving systems know that it is also a matter of prior transmission of the start of the program and therefore store these data units. (It should be noted that this marking can be implicit; for example, all recipients can know that the first 120 seconds of a program should always be saved.) The individual data units may be sent repeatedly (e.g. at ever larger intervals, as in Fig can be indicated. 5, or by providing each data unit D1,..., m Dv time is in each case transmitted in accordance with transmission schedule) starting until finally the fact that all recipients who previously received data to be distributed units. Then the sender stops sending them and falls into the intended schedule of a real-time transmission, which can fall back on previously transmitted data units.
• The pre-transmission of the data units at the beginning of the program can also be modified in such a way that the data units are transmitted in a channel that is independent of the real-time transmission (for example as part of a file distribution). In this case, an additional channel (possibly with a different bandwidth and different transmission format) is used for the preliminary transmission of the data units). In contrast to pure advance transmission, however, this happens at least partially in parallel with the real-time transmission of the program.
• - Likewise, such a distribution (with a much lower data rate) can be permanently active in the background, so that all potential viewers can be given the program start to be distributed in advance during the first (short) period of real-time transmission. Here too, a separate data channel is required for permanent advance transmission.

With these methods the necessary for the transmission of a live program can be Significantly reduce bandwidth. At the beginning of the live program, it is just as high like real-time transmission without advance distribution. As soon as (e.g. after repeated Send) the integrated advance transmission of the data units is set, this requires Process only the data rate necessary for the transmission of a "canned" program would be required.

The additionally required transfer rate to the integrated (or separately pre-transfer occurs only at the beginning - at a time when not all data units are yet available and therefore (as described in 3.1) still the maximum bandwidth is not required for the transmission of the program. By A suitable overall embedding of the advance transmission can thus be an overall data rate achieve, which is below the maximum bandwidth required for the program.

3.3 Consideration of the available storage space at the receivers

The methods described as prior art require that the receiving systems with enough memory is available to store the previously distributed shares to save several (potentially many) programs permanently (at least until that Broadcast interval of a program is over). Besides, is for that just considered Program memory on the order of approximately 40-60% of the program is required.

Here is an example: Consider a feature film with a program duration of two Hours (7200 seconds) digitized using the MPEG-2 encoding method (MPEG-2 is the standard for DVDs and digital TV). The encoding is based on a data rate of around 2 Mbit / s, the data volume for the entire feature film is around 2 GB. If 50% has to be saved, there is a requirement of around 1 GB. If the first four minutes are transmitted in advance, the receiver must have around 50 MB Save data permanently.

These storage requirements can generally only be met today by using Meet hard drives.

The requirement for the storage capacity on the receiving system results from the Frequency with which a single data unit is transmitted. Because a data unit must be saved if they are not repeated by the broadcaster before the time of playback is transmitted. For example, if you double the transmission frequency of one Data unit, the space required for this is statistically halved because it only averages must be kept half as long.

• a) Statische Adaption: Dem Sender ist der minimal in allen Empfangssystemen für das Abspielen (und ggf. das Vorab-Übertragen) eines Programms zur Verfügung stehende Speicherplatz bekannt. Diese untere Grenze ändert sich während der Übertragung eines Programms nicht und wird bei der Berechnung des Sendeplans berücksichtigt.
• b) Dynamische Adaption: Dem Sender wird der Speicherplatz genau der Empfangssysteme, die ein Programm betrachten wollen, über einen Rückkanal mitgeteilt (z. B. bei der "Anforderung" des Programms). Für jeden Einstiegszeitpunkt speichert der Sender die minimal verfügbare Speicherkapazität der Empfänger, die zu diesem Einstiegszeitpunkt mit dem Betrachten eines Programms begonnen haben. Neue Anforderungen von Empfängern werden benutzt, um den Sendeplan dynamisch so anzupassen, daß die Anforderungen an die Speicherkapazität die Leistungsfähigkeit der Empfänger nicht übersteigen.

The existing methods can be improved in such a way that they take into account the memory limits of the receiving systems and adapt the transmission schedule with the inclusion of this information. Two different approaches (which can be smoothly converted into one another) can be followed first:

• a) Static adaptation: The transmitter is aware of the minimal amount of memory available in all receiving systems for playing (and possibly pre-transmitting) a program. This lower limit does not change during the transmission of a program and is taken into account when calculating the transmission schedule.
• b) Dynamic adaptation: The transmitter is informed of the storage space of exactly the receiving systems that want to view a program via a return channel (eg when the program is "requested"). For each entry point, the transmitter stores the minimum available storage capacity of the receivers who started viewing a program at this entry point. New requirements of receivers are used to dynamically adapt the transmission schedule so that the requirements for the storage capacity do not exceed the performance of the receivers.

• - Im Falle dynamischer Adaption kann der Sendeplan einfach genau an die aktuellen Anforderungen angepaßt werden; dabei wird in Kauf genommen, daß die zur Übertragung der Dateneinheiten erforderliche Bandbreite nicht konstant ist, sondern je nach Anforderungssituation variieren kann (und insbesondere die Bandbreite einer regulären Echtzeit- Übertragung ohne Speicheranpassung übersteigen kann). Um die Variabilität in Grenzen zu halten, können eintreffende Anforderungen ggf. um einige (wenige) Zeitintervalle Δt verzögert werden.
• - Im Falle statischer und dynamischer Adaption ist der tatsächliche (im Gegensatz zum mittleren) Speicherbedarf abhängig von dem tatsächlichen Einstiegszeitpunkt; bereits geringe zusätzlich herbeigeführte Verzögerungen auf der Seite des Empfängers können diese Anforderungen reduzieren.
• - Im Falle statischer (und in Grenzen dynamischer) Adaption läßt sich der mittlere Speicherbedarfreduzieren, indem die zu speichernden Dateneinheiten häufiger gesendet werden. Dies gilt insbesondere für die "höheren" Kanäle, in denen die Dateneinheiten sehr selten übertragen werden. Verdoppelt man beispielsweise die Datenrate eines Kanals, so reduziert man den mittleren Speicherbedarf für die Dateneinheiten dieses Kanals auf die Hälfte.
• - Die im vorigen Punkt angesprochene Erhöhung der Datenrate resultiert daraus, daß die einzelnen Dateneinheiten eines oder mehrerer Kanäle verglichen mit dem Grundschema mehrfach gesendet werden. Dieses Verfahren läßt sich durch Einsatz von mathematischen Verfahren der Vorwärtsfehlerkorrektur (Forward Error Correction, FEC) optimieren.
  Ganz allgemein wird hier davon ausgegangen, daß zur Übertragung des Inhalts von m Dateneinheiten m + l Dateneinheiten gesendet werden. Dabei werden die l zusätzlichen Dateneinheiten (die Redundanzinformationen) so berechnet, daß sich die m ursprünglichen Dateneinheiten rekonstruieren lassen, wenn aus den m + l Dateneinheiten mindestens m beliebige empfangen werden. In der einfachsten Form wird für l = 1 die Funktion "exklusiv Oder (XOR)" eingesetzt. Allerdings sind auch rechenintensivere Verfahren (z. B. Vandermonde-Matrizen) oder ähnliche mathematische Ansätze in diesem Verfahren einsetzbar.
  Durch Einsatz eines XOR-Verfahrens (das hier als Beispiel beschrieben werden soll) kann folgendes Szenario umgesetzt werden: Der Sendeplan wird in einem einfachen Fall so modifiziert, daß in dem Zusatzkanal nicht ein vollständiger Kanal repliziert wird. Statt dessen wird zu jeweils mindestens zwei Dateneinheiten (z. B. Di und Dj) im Zusatzkanal die Information Dij = Di XOR Dj gesendet. Ein Empfänger, der vorher nur Dj empfangen hat und auf Di wartet, kann aus Dij einfach Di = Dij XOR Dj rekonstruieren; ein Empfänder, der nur Di empfangen hat und auf Dj wartet, kann entsprechend hieraus Dj rekonstruieren. Da statt zwei (oder mehr) Dateneinheiten nur eine zusätzlich gesendet wird, reduziert sich die zusätzlich erforderliche Bandbreite (hier im Beispiel auf die Hälfte). In einem zusätzlichen Kanal können so beispielsweise die Zusatz-Informationen zweier originärer Kanäle versendet werden.
• - Schließlich lassen sich Verfahren des Staggered Broadcasting und der eingangs skizzierten Echtzeit-Übertragung miteinander verknüpfen. Werden mehrere Datenströme versetzt gesendet, so kann ein Empfänger immer auf den "nächsten" dieser Datenströme zurückgreifen. Bei k_s die Anzahl der für ein Programm vorgesehenen NVoD-Kanäle (die jeweils im Abstand von T_a/k_s zyklisch ausgesendet werden, wobei T_a die Länge des Programms angibt). Dann muß ein Echtzeit-Übertragungsverfahren nur noch auf den ersten Programmteil der Länge T_a/k_s angewendet werden (wie in Fig. 6 für k_s = 4 dargestellt). Der Speicherbedarf sinkt von rund 50% des gesamten Films auf 50% von 1/k_s des gesamten Films. Zusätzlich müssen noch maximal die Dateneinheiten des Zeitraum T_a/k_s - Δt gespeichert werden können; nämlich genau dann, wenn der Zyklus eines NVoD-Stroms knapp (um Δt) verpaßt wurde.
  Der Speicherbedarf ergibt sich aus der zu speichernden Zeit des Programms:
  
  T_B = T_s/k_s + 0,5 × T_s/k_s - Δt
  
  was für k_s > 3 weniger als 0,5 T_s ausmacht und damit zu einer Einsparung an Speicherplatz führt.
  Zu beachten ist weiterhin, daß die Skizze in Fig. 6 eine Optimierung für die Zusatzkanäle zur Echtzeit-Übertragung offen läßt: in den Zusatzkanälen werden hier auch die Dateneinheiten gesendet, die zum selben Zeitpunkt in einem der NVoD-Kanäle übertragen werden.

The transmitter has the following options to address the limitations of the receiving systems:

• - In the case of dynamic adaptation, the transmission schedule can simply be adapted precisely to the current requirements; it is accepted that the bandwidth required for the transmission of the data units is not constant, but can vary depending on the requirement situation (and in particular can exceed the bandwidth of a regular real-time transmission without memory adaptation). In order to keep the variability within limits, incoming requests can possibly be delayed by a few (a few) time intervals Δt.
• - In the case of static and dynamic adaptation, the actual (as opposed to the average) memory requirement depends on the actual entry time; Even minor delays on the receiver side can reduce these requirements.
• In the case of static (and within limits dynamic) adaptation, the average memory requirement can be reduced by sending the data units to be stored more frequently. This applies in particular to the "higher" channels, in which the data units are transmitted very rarely. If you double the data rate of a channel, for example, you reduce the average memory requirement for the data units of this channel by half.
• - The increase in the data rate mentioned in the previous point results from the fact that the individual data units of one or more channels are sent several times compared to the basic scheme. This method can be optimized by using mathematical methods of forward error correction (FEC).
  In general, it is assumed here that m + 1 data units are sent to transmit the content of m data units. The l additional data units (the redundancy information) are calculated so that the m original data units can be reconstructed if at least m any number are received from the m + l data units. In the simplest form, the function "exclusive OR (XOR)" is used for l = 1. However, more computationally intensive processes (e.g. Vandermonde matrices) or similar mathematical approaches can also be used in this process.
  The following scenario can be implemented by using an XOR method (which is described here as an example): The transmission schedule is modified in a simple case in such a way that a complete channel is not replicated in the additional channel. Instead, the information Dij = Di XOR Dj is sent to at least two data units (e.g. Di and Dj) in the additional channel. A receiver who has previously only received Dj and is waiting for Di can simply reconstruct Di = Dij XOR Dj from Dij; a recipient who has only received Di and is waiting for Dj can accordingly reconstruct Dj from this. Since only one additional data unit is sent instead of two (or more), the additional bandwidth required is reduced (in this example by half). For example, the additional information of two original channels can be sent in an additional channel.
• - Finally, methods of staggered broadcasting and the real-time transmission outlined at the beginning can be linked. If several data streams are sent offset, a receiver can always access the "next" of these data streams. At k_s the number of NVoD channels provided for a program (which are transmitted cyclically at intervals of T_a / k_s, where T_a indicates the length of the program). A real-time transmission method then only has to be applied to the first program part of length T_a / k_s (as shown in FIG. 6 for k_s = 4). The memory requirement drops from around 50% of the entire film to 50% of 1 / k_s of the entire film. In addition, a maximum of the data units of the period T_a / k_s - Δt must be able to be stored; namely, if the cycle of an NVoD current was missed just by (by Δt).
  The memory requirement results from the time to be saved in the program:
  
  T_B = T_s / k_s + 0.5 × T_s / k_s - Δt
  
  which is less than 0.5 T_s for k_s> 3 and thus leads to a saving in storage space.
  It should also be noted that the sketch in Fig. 6 leaves an optimization for the additional channels for real-time transmission open: in the additional channels, the data units that are transmitted at the same time in one of the NVoD channels are also sent here.

All of these approaches can be used individually or in combination - and they are not for the broadcast schedule described as an example.

3.4 Multiple use of program parts

In connection with the pre-transmission of program parts (typically each the beginning of a program) and the storage of these program parts by the A further optimization can be achieved: this leads to a reduction in the for the Bandwidth required as well as that on the receiving systems necessary storage space.

• - Spielfilme beginnen meist mit einem "Intro" des Filmverleihs, der Produktionsfirma o. ä. Wenn verschiedene Spielfilm aus demselben Hause stammen, sind diese "Intros" i. d. R. identisch.
• - Nachrichtensendungen, Reportagen, Serien usw. haben oftmals den gleichen Vorspann. Werden mehrere Sendungen oder Episoden in zeitlicher Nähe übertragen, so läßt sich der Vorspann wiederverwenden.
• - Vor unterschiedlichen Spielfilmen werden oft dieselben "Trailer" oder dieselbe genrespezifische Werbung gezeigt, so daß auch diese Programmteile identisch sind.
• - Jingles im Rundfunk (wie auch vielleicht im Fernsehen) wiederholen sich.

The starting point is the observation that many programs often start out the same way (or at least contain the same parts in the first few minutes), as the following examples will demonstrate (see also Fig. 7):

• - Feature films usually begin with an "intro" from the film distributor, the production company or similar. If different feature films come from the same company, these "intros" are usually identical.
• - News programs, reports, series, etc. often have the same opening credits. If several programs or episodes are broadcast in close proximity, the opening credits can be reused.
• - The same "trailer" or the same genre-specific advertisement is often shown in front of different feature films, so that these program parts are also identical.
• - Jingles on the radio (like maybe on TV) repeat themselves.

Further examples can be found here. It is essential that there are program parts which are part of different programs in the same form.

Formally speaking, there is a program part P, which consists of the data units Pi with p_a ≤ i ≤ p_e, where p_a ≥ 1 and p_e ≤ n and p_l = p_e - p_a (if a program consists of n data units), so that for all Pi with with p_a ≤ i ≤ p_e and at least two programs D and E applies:
Pi = Dj and Pi = Ek.

In such a case, it may be useful to have a unique program part P Identifiers (e.g. a number, an object identifier, a file name or a URL / URI) provided in order to be able to refer to it from elsewhere.

In the case of a preliminary transmission, such a program part P then only has to be transmitted once, even if it is part of several programs. This advance transfer can take place as a separate program part in one or more separate files or as part of a program (as part of one or more files). In the latter case, additional information is required, e.g. B. encoded into the identifier or stored by means of the identifier. This additional information must at least indicate which part of the program belongs to the reusable program part P. This can be done by specifying the start and end (for video, for example, as an hour, minute, second, single image, for audio, for example, as an hour, minute, second, sample or generally also as a data unit) or the start and duration , In a program D, the program part P need not be transmitted if P was transmitted as a separate or as part of another program. Program D then only requires a reference (by means of a unique identifier) to P and the information on where program part P is to be used in program D (which in turn can be done by simply specifying the start and end or the start and duration) , See Fig. 7. It should also be pointed out that the entire program part P does not necessarily have to be used for this in another program, but that sections of P can also be referenced.

In the case of real-time transmission, this method can be used analogously, by instead of a data unit a reference to another program (in advance) transmitted data unit is sent. It can be used during real-time transmission Program on pre-transferred parts of another program or on in real time transferred parts of another program. This procedure can used individually or in combination with others (described here).

Claims (1)

Method for transmitting electronic data streams, in particular multimedia data streams, between at least one transmitting device and at least one receiving device, in which:
an electronic data stream D1, which is formed by a plurality of data units E1_i (i = 1, 2, 3,...), with the aid of a plurality of data quantities M1_j (j = 1, 2, 3,...) starting from a start time t1_s from the transmitting device is transmitted over several transmission channels, so that a complete reproduction of the electronic data stream D1, in particular of picture and / or sound information, can be started by means of the at least one receiving device at several reproduction times from the start time t1_s, the complete reproduction of the electronic data flow D1 can be started at the latest at a last playback time t1_e;
with part of the plurality of data sets M1_j, only part of the plurality of data units E1_i is transmitted;
a further electronic data stream D2, which is formed by a plurality of data units E2_i (i = 1, 2, 3,...), with the aid of a plurality of data sets M2_j (j = 1, 2, 3,...) starting from a further start time t2_s is transmitted by the transmitting device over at least part of the plurality of transmission channels, so that a complete reproduction of the electronic data stream D2, in particular of picture and / or sound information, can be started by means of the at least one receiving device at different reproduction times from the further start time t2_s; and
During a transition period Δtü, which begins at the further start time t2_s, both a subset of data units E1_n, which is formed by part of the data units E1_i, and at least a subset of the data units E2_i are transmitted from the at least one transmitting device to the at least one receiving device , wherein the subset of data units E1_n sent during the transition period Δtü is formed by the part of the data units E1_i which were not transmitted between the last playback time t1_e and the further start time t2_s.