WO2008014707A1 - Method, system and terminal of adjusting video quality - Google Patents

Abstract

The invention discloses method, system and terminal of adjusting video quality, including: sender extracts default coding-rank table items from the preset coding rank table corresponding to different network conditions, and sets up video connection and transmits RTCP (real-time transport control protocol) packages according to parameters of the table items; receiver judges network conditions and returns them to sender according to the RTCP packages; sender adjusts current coding-rank table items according to the judging results, to avoid estimating network bandwidth incorrectly and affecting video transmission quality.

Description

 Method, system and terminal for adjusting video quality

 The present invention relates to the field of video communications, and more particularly to a method, system and terminal for adjusting video quality. Background of the invention

 With the rapid development of the Internet and the maturity of multimedia technology, the market for video communication is becoming more and more widely used, and the ways to realize video communication have become various, such as videophone, instant messaging, video chat, IPTV, remote monitoring. , as well as telemedicine. The broad prospects for video communication development make it another important form of communication following voice communication.

 Video communication is typically carried out over a dedicated or public communication network by point-to-point or point-to-multipoint transmission of video data. From the perspective of users expecting wider communication and lower cost, the public network will be the user's first choice. Due to the real-time and interactivity requirements of video communication, the network carrying video communication must be able to guarantee the smoothness and quality of the video.

 At present, the IP of communication networks has become the mainstream of network development, and video communication based on IP networks has been widely applied and widely developed. The IP network is a connectionless network using the TCP/IP protocol. The H.323 standard is a video communication standard developed by ITU-T in 1996 for IP networks. The H.323 standard is a video communication with a large number of commercial users. Standards are widely recognized and widely used.

The IP network carrying video communication must first face the bandwidth problem. Take video chat as an example. According to the empirical value, using the popular H.263 coding standard, to ensure acceptable quality and smoothness, the network bandwidth is required to be 128 ~ 256kbit/s. Due to the interactive communication, plus the load of the network transmission, an actual point-to-point video call may occupy this bandwidth. 2.5 times (320 ~ 640kbit/s). Therefore, video communication needs to consume a large amount of network bandwidth. To ensure quality of service (QoS) parameters under various networks, such as the Internet and the local area network, it is necessary to perform bandwidth control through video quality adjustment.

 Second, video communication is sensitive to delay and jitter, so video transmission generally uses the real-time User Data Packet Protocol (UDP). However, since the UDP protocol does not have any congestion control algorithm, it is easy to cause network overload and high packet loss rate, thus affecting the video transmission quality. Therefore, video communication also requires real-time transport protocol/real-time transport control protocol (RTP/RTCP) support. RTP and RTCP combine to provide flow control and congestion control for the network. During the RTP session, each participant periodically transmits RTCP packets, which contain statistics such as the number of transmitted packets and the number of lost packets, which are used to determine the network status for dynamic video quality adjustment. mostly according.

 At present, the quality control of video transmission generally has the following options:

 1. The minimum transmitted video coding. That is, the video stream is generated by the encoder for transmission according to the minimum acceptable bandwidth. The main disadvantage of this solution is that video transmission lacks the flexibility to adapt to dynamic network changes.

 2. Transcoding technology. That is, a compressed video data of sufficient quality is stored in the server. When the output bit rate needs to be reduced, the server only needs to perform partial decoding and encoding to output a suitable video data stream.

 3. Code stream switching technology. The server stores multiple copies of different qualities of the same video program. The I frames of these streams are aligned, and the server selects an appropriate code stream to send to the user according to the bandwidth of the user network. The I frame refers to a video coding type, also called a key frame, which can be accessed without being dependent on other frames, and can be accessed at any time by another stream.

 The transcoding technology and the code stream switching technology described in the schemes 2 and 3 greatly increase the storage cost of the server in order to increase the flexibility.

4. Adaptive video coding. That is, the encoder parameters are automatically adjusted according to changes in the network environment. Number, the encoding method that adapts the code rate of the output code stream to the network change. Generally, the sender divides the compressed data stream into RTP protocol packets and sends them to the receiver. The receiver monitors the transmission delay and packet loss rate of the RTP data packet, and feeds back the network transmission status to the sender through the RTCP protocol in the RTP protocol. The sender adjusts the data transmission rate according to the network bandwidth to match the network environment. This scheme is a more flexible one of the existing methods, but it needs to estimate the current network bandwidth value and adjust the data transmission rate according to this. The quality of the video transmission will be affected when the estimation is not accurate. Summary of the invention

 In view of this, the main purpose of the embodiments of the present invention is to provide a method, a system, and a terminal for adjusting video quality, without estimating the current network bandwidth value, and ensuring video transmission quality.

 To achieve the above objective, the technical solution of the embodiment of the present invention is specifically implemented as follows: The method of the present invention includes the following steps:

 The sender extracts a default level entry from a preset encoding level table corresponding to different network conditions, establishes a video connection with the parameters in the entry, and sends a real-time transmission control protocol RTCP packet;

 The receiver judges the network status according to the received RTCP packet and returns it to the sender, and the sender adjusts the current coding level entry according to the judgment result.

 In order to support the method of the present invention, embodiments of the present invention also provide a sender terminal, a receiver terminal, and a corresponding system.

 The sender terminal includes: a coding unit, configured to: encode the video stream according to the input parameter, and send the encoded video code stream to the receiver terminal; and the RTCP packet sending unit is configured to send the RTCP packet to the receiver terminal; The sender terminal further includes:

 An encoding level table storage unit, configured to preset a coding level table;

a level entry extraction unit, configured to determine a result according to the received network condition, from the Page, and output the parameters in the extracted level table item to the coding unit.

 The receiving terminal includes: a decoding unit, configured to decode the received video code stream; and an RTCP packet receiving unit, configured to receive the RTCP packet, determine the network status according to the information in the RTCP packet, and feed back the determination result to the sender terminal; The receiver terminal further includes:

 The second terminal capability acquiring unit is configured to acquire the terminal capability of the local end, and send the terminal capability to the sender terminal.

 a system for adjusting video quality, comprising: a receiver terminal, configured to decode a received video stream, and determine a network status according to the received information in the RTCP packet, and feed back the judgment result to the sender terminal; The system also includes:

 The sender terminal is configured to send the encoded video code stream and the RTCP packet, and extract the corresponding level entry from the preset coding level table according to the network status judgment result fed back by the receiver terminal, and use the level entry The parameters in the code are encoded.

 It can be seen from the above technical solution that the present invention does not need to estimate the current network bandwidth value when performing video quality adjustment, thereby avoiding the problem that the video transmission quality is affected when the estimation is not accurate, thereby ensuring the video transmission quality.

BRIEF DESCRIPTION OF THE DRAWINGS

 Figure 1 is a schematic structural view of a system of the present invention;

 2 is a schematic structural diagram of a sender terminal according to the present invention;

 3 is a schematic structural diagram of a receiver terminal according to the present invention;

Figure 4 is a flow chart of the method of the present invention. Mode for carrying out the invention

 In order to perform video quality adjustment, it is not necessary to estimate the current network bandwidth value, thereby avoiding the problem that the video transmission quality is affected when the estimation is not accurate. The present invention provides a system for adjusting video quality, as shown in FIG. The system includes: a sender terminal 1 and a receiver terminal 2.

 The sender terminal 1 is configured to send the encoded video code stream and the RTCP packet, and extract a corresponding level entry from the preset coding level table according to the network status judgment result fed back by the receiver terminal 2, and The parameters in this level entry are encoded.

 The receiver terminal 2 is configured to decode the received video code stream, determine the network status according to the information in the received RTCP packet, and feed back the determination result to the sender terminal 1.

 2 is a schematic structural diagram of a sender terminal according to the present invention. Referring to FIG. 2, the sender terminal 1 (ie, the sender terminal of the present invention) in the above system mainly includes: an RTCP packet sending unit 11 and a level table entry extracting unit. 12, and an encoding level table storage unit 13 and an encoding unit 14 connected to the level entry extraction unit 12;

 The RTCP packet sending unit 11 is configured to send an RTCP packet to the receiver terminal 2.

 The level entry extraction unit 12 is configured to extract a corresponding level entry from the encoding level table stored by the encoding level table storage unit 13 according to the received network status determination result, and output the parameter in the extracted level entry to the Encoding unit 14.

 The encoding level table storage unit 13 is configured to store a preset encoding level table.

 The encoding unit 14 is configured to encode the video stream according to the input parameters and send it to the receiver terminal 2.

Further, in order to reduce the impact of the terminal capabilities of the transmitting and receiving parties on the video quality and the fluency, the sender terminal further includes a first terminal capability acquiring unit 15 and a highest video frame rate determining unit 16, which are connected to each other, and the highest video frame. The rate determining unit 16 is also connected to the encoding level table storage unit 13; The first terminal capability acquiring unit 15 is configured to acquire the terminal capability of the local end.

 The highest video frame rate determining unit 16 is configured to determine a highest video frame rate by using the terminal capability of the local end and a lower terminal capability of the terminal capability sent by the receiving terminal, and storing the high video frame rate and the encoding level table. Unit 13 interacts to determine the level table entries available in the encoding level table accordingly.

 Further, in order to reduce the impact of the RTCP packet on the network load, the sender terminal further includes an adaptation unit 17 connected to the RTCP packet sending unit 11 for controlling the RTCP packet sending unit at an adaptive time interval. 11 Send the RTCP packet.

 3 is a schematic structural diagram of a receiver terminal according to the present invention. Referring to FIG. 3, the receiver terminal 2 (ie, the receiver terminal of the present invention) in the above system includes: a decoding unit 21 and an RTCP packet receiving unit 22;

 The decoding unit 21 is configured to decode the received video code stream.

 The RTCP packet receiving unit 22 is configured to receive the RTCP packet, determine the network status according to the information in the RTCP packet, and feed back the judgment result to the sender terminal 1.

 Further, in order to reduce the impact of the terminal capability of the transmitting and receiving parties on the video quality and the fluency, the receiving terminal further includes a second terminal capability acquiring unit 23, configured to acquire the terminal capability of the local end, and send the terminal capability to the transmitting terminal 1.

 Applying the above system and terminal, the present invention provides a method for adjusting video quality, and FIG. 4 is a flow chart of the method of the present invention. Referring to FIG. 4, the following main steps are included:

 S1. Extract a default level entry from a preset encoding level table.

 First, a coding level table is preset in the sender terminal. The coding level table includes several level entries to suit different network conditions. The higher the level entry, the better the network condition is applicable to each parameter value. On the contrary, the lower the level entry, the worse the network condition of each parameter value is.

As shown in Table 1, each level entry in the encoding level table can include the following parameters: Key frame I frame interval, quality priority or speed priority, quality priority bandwidth, quality priority frame rate, speed priority bandwidth, and speed priority frame rate; in addition, to increase rate control The flexibility of each level table can also include: horizontal scaling of the video window, and vertical scaling of the video window. For example: Level 9 entry = { 100, 0, 300, 12, 200, 13, 4/5, 1 } means that at level 9, the encoder will insert an I frame every 100 frames, select the speed priority mode. The bandwidth and frame rate under quality priority are 300k and 12 frames respectively, the bandwidth and frame rate in speed priority mode are 200k and 13 frames respectively, the horizontal scaling of video window is 4/5, and the vertical scaling of video window is 1. .

表一

Table I

 Second, you can choose to detect the terminal capabilities of both the sender and the receiver.

 Compared with the traditional coding standard, the H.264 standard can increase coding efficiency by about 50%, but its terminal capability requirements will also increase exponentially. If the decoding capability of the receiver terminal is insufficient, the encoding frame rate of the sender terminal must be controlled to prevent the receiver terminal from dropping the frame due to decoding, resulting in a video that is not smooth.

Therefore, in order to take into account the terminal capabilities of both senders and receivers, in order to achieve better video effects, Before establishing a video connection, you can choose to detect the terminal capabilities of both the sender and the receiver. The highest video frame rate is determined by the lower terminal capability of the terminal capabilities of the transmitting and receiving parties, and the level table item available in the encoding level table is determined correspondingly by the highest video frame rate.

 In the video stream encoding and decoding process, the terminal capability is mainly reflected in the processing power of the CPU.

The processing power of the CPU is mainly determined by the CPU frequency, but in addition to the main frequency, other factors (such as the Cache size) also have an impact on the processing power of the CPU. Therefore, the highest video frame rate is correspondingly based on the CPU main frequency, for example: 2700 MHz main frequency corresponds to 15 frames, and 400 MHz main frequency corresponds to 1 frame. Further, comprehensively consider the characteristics of the CPU type and the size of the first-level cache Cache to correct the highest corresponding video frame rate, for example: For the AMD chip, the level 2 Cache size exceeds 128 and the frame rate is increased by 1, more than 256. The frame rate is increased by 2.

 Finally, the default level entry is extracted from the preset encoding level table by using the highest video frame rate. The default level entry should select a lower level entry to ensure that the video connection is successfully established.

 52. Establish a video connection with the parameters in the default level entry.

 53. Send the RTCP packet.

 After the video connection is established, the sender terminal sends an RTCP packet to the receiver terminal. The transmitted RTCP packet contains information such as packet loss rate, network jitter, and delay time.

This step can further adopt a method of transmitting an RTCP packet at a certain length of time. When the video connection is just established, the time interval for sending packets is shorter to quickly determine the network status. After the video connection is stable, the time interval for sending packets should be gradually lengthened to reduce the network load caused by the RTCP packet. Therefore, the present invention preferably transceives RTCP packets at adaptive time intervals. The adaptive time interval is calculated by the following formula: Time interval for transmitting RTCP packets = (time when video has been established) X ( EXP (I frame interval time / 125 ) -1 ), that is, the time interval for transmitting the RTCP packets For: Calculate the exponent of the quotient of the I frame interval time and the constant 125, and obtain the difference between the obtained value and the constant, and then calculate the difference and the video has been established. The product of time.

 S4. Receive an RTCP packet to determine the network status.

 After receiving the RTCP packet sent by the sender terminal, the receiver terminal obtains the relevant information, and if the received packet loss rate, network jitter, and delay time in the RTCP packet are less than the corresponding threshold, the network condition is determined to be good. Otherwise, it is determined that the network is not in good condition.

 S5. Adjust the current coding level entry according to the judgment result.

 The receiver terminal feeds back the network status judgment result to the sender terminal. If the judgment result received by the sender terminal indicates that the current network condition is good, and there is room for improving the video quality and fluency, the current coding level entry is used to be encoded, thereby generating a higher quality video bitstream, and receiving If the judgment result received by the sender terminal indicates that the current network status is not good, that is, the currently used coding level entry has exceeded the adaptability of the current network condition, the current coding level entry is lowered. The code generates a video stream of lower quality and transmits it to the receiver terminal.

 The above is only the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modifications, equivalents, improvements, etc., which are made within the spirit and principles of the present invention, should be included. It is within the scope of the invention.

Claims

Claim A method for adjusting video quality, comprising the steps of: the sender extracts a default level entry from a preset encoding level table corresponding to different network conditions, and establishes a video connection by using parameters in the entry; And send real-time transmission control protocol RTCP package;  The receiver judges the network status according to the received RTCP packet and returns it to the sender, and the sender adjusts the current coding level entry according to the judgment result.  2. The method according to claim 1, wherein each level entry in the coding level table includes the following parameters:  Keyframe I frame interval, quality priority or speed priority, quality priority bandwidth, quality priority frame rate, speed priority bandwidth, speed priority frame rate, video window horizontal scaling, and video The vertical scale of the window.  The method according to claim 1, wherein the receiving party compares the preset threshold with the information carried in the received RTCP packet to determine the network status, and adjusts the current coding level table according to the determination result. item.  4. The method according to claim 3, wherein the received RTCP packet includes a packet loss rate, a network jitter, and a delay time; and the method for the receiver to determine the network status is:  When the packet loss rate, network jitter, and delay time in the received RTCP packet are less than the corresponding threshold, the network condition is determined to be good, and the coding level entry used is raised; , and lower the encoding level table used. The method according to claim 1, wherein the method further comprises: the sender and the receiver respectively acquire respective terminal capabilities, and the receiver sends the obtained terminal capability to the sender, and the sender transmits and receives the Lower terminal capability determination in terminal capabilities The highest video frame rate, and the highest video frame rate, determines the level table entries available in the encoding level table.  The method according to claim 5, wherein the terminal capability comprises: a CPU frequency of the terminal.  The method according to claim 6, wherein the terminal capability further comprises: a size of the primary cache Cache of the terminal, and/or a size of the secondary cache of the terminal.  The method according to claim 1, wherein the method of transmitting the RTCP packet is: transmitting the RTCP packet at an adaptive time interval.  9. The method according to claim 8, wherein the adaptive time interval is: calculating an exponent of the quotient of the I frame interval time and the constant 125, and the obtained value is reduced by a constant, and then the difference is calculated. The product of the time the video has been created.  10. A sender terminal, comprising:  a coding unit, configured to: encode the video stream according to the input parameter, and send the encoded video code stream to the receiver terminal; and the RTCP packet sending unit is configured to send the RTCP packet to the receiver terminal;  The sender terminal further includes:  An encoding level table storage unit, configured to preset a coding level table;  The level entry extraction unit is configured to output the parameter from the edited level entry to the coding unit according to the received network status determination result.  The sender terminal according to claim 10, wherein the terminal further comprises:  The first terminal capability acquiring unit is configured to acquire the terminal capability of the local end; The highest video frame rate determining unit is configured to send the terminal capability of the local end and the receiving terminal The lower terminal capability of the terminal capabilities determines the highest video frame rate, and interacts with the encoding level table storage unit at the highest video frame rate to determine the level entries available in the encoding level table.  The sender terminal according to claim 10, wherein the sender terminal further comprises:  And an adaptive unit, configured to control the RTCP packet sending unit to send the RTCP packet at an adaptive time interval.  13. A receiver terminal, comprising:  a decoding unit, configured to decode the received video code stream;  The RTCP packet receiving unit is configured to receive the RTCP packet, determine the network status according to the information in the RTCP packet, and feed back the judgment result to the sender terminal;  The receiver terminal further includes:  The second terminal capability acquiring unit is configured to acquire the terminal capability of the local end, and send the terminal capability to the sender terminal.  14. A system for adjusting video quality, comprising:  The receiver terminal is configured to decode the received video code stream, determine the network status according to the information in the received RTCP packet, and feed back the determination result to the sender terminal;  The system further includes:  The sender terminal is configured to send the encoded video code stream and the RTCP packet, and extract the corresponding level entry from the preset coding level table according to the network status judgment result fed back by the receiver terminal, and use the level entry The parameters in the code are encoded.  The system according to claim 14, wherein the receiver terminal is further configured to acquire the terminal capability of the local end, and send the terminal capability to the sender terminal; The sender terminal is further configured to acquire the terminal capability of the local end, and determine the highest video frame rate by using the terminal capability of the local end and the lower terminal capability of the terminal capability sent by the receiver terminal, and the highest video frame rate is The coding level table storage unit interacts to determine the coding The level table items available in the level table.  The system according to claim 14 or 15, wherein the sender terminal is further configured to control the RTCP packet sending unit to send an RTCP packet at an adaptive time interval.