JP2004096474A - Video data playback method and playback device - Google Patents

Abstract

Kind Code: A1 The present invention relates to a method for playing back moving image data, and more particularly to a method for playing back MPEG data that can randomly access MPEG data stored in VBR.
The playback method includes storing, in a table, an average bit rate calculated from time information of the beginning and end of accumulated moving image data, a randomly accessible image group and a last image group at the beginning of the moving image data. Detecting and storing the time information and position information, further calculating the image group unit time based on the number of frames between adjacent image groups and storing the calculated time in the table, the average bit rate stored in the table, and the like. Calculating a point to be accessed, starting reproduction from the calculated point to be accessed and the time information and position information of the image group detected in the reproduction process, and based on the information. And storing the calculated average bit rate between the image groups in the table.
[Selection diagram] Fig. 4

Description

【００２７】
図１０には、上記式で算出した総再生時間を用いて、ファイルのバイトサイズ（総バイト数）から平均ビットレート（本例では４Ｍｂｐｓ）を算出した例を示している。これより、先頭ＧＯＰ及び最終ＧＯＰの各々のＧＯＰ時間とバイト位置、そして先頭ＧＯＰと最終ＧＯＰとの間の平均ビットレートが求まる。このように、ファイル再生に必要な最小限の情報をその再生開始前に取得することで、該当ＭＰＥＧファイルの特殊再生を行うための初期管理テーブル７が作成される（Ｓ１０６）。
【００２８】
本発明では、ＭＰＥＧ蓄積データからのみデータの平均ビットレートを計算し、且つ蓄積ファイルの先頭及び最終部分のみのサーチで済むため、再生開始時点でのサーチ量が少なく、従来のインデックスファイルを作成するようなシステムよりも高速に再生が開始される。
【００２９】
（２）先頭から順方向に再生する場合
図５には、順方向再生時の制御フローの一例を示している。また、図１１には、順方向再生における管理テーブル７の更新の一例を示している。
【００３０】
ＤＥＭＵＸ４は、外部制御部３からの順方向再生指示により、蓄積データ読み込み部２を制御して一連の蓄積データを復号・再生のためにシーケンシャルに読み込む（Ｓ２０１）。その復号・再生過程で（Ｓ２０４）、実際に検出されたＧＯＰ毎の時間やＧＯＰ毎の蓄積データのバイト位置からＧＯＰ毎のビットレートを算出し、その情報によって管理テーブル７の内容を保存・更新していく（Ｓ２０２及び２０３）。
【００３１】
図１１の例では、順方向の再生過程でＧＯＰ検出部６が検出した情報を元に算出された２番目、３番目、…、のＧＯＰ毎の時間、ＧＯＰ毎のバイト位置、及びＧＯＰ毎の平均ビットレートが先頭ＧＯＰと最終ＧＯＰとの間に挿入され保存されていく。
【００３２】
（３）管理テーブルにＧＯＰのバイト位置が登録されていない時間にシーク指示が発生した場合
図６及び７には、シーク指示による制御フローの一例を示している。また、図１２及び１３には、管理テーブル７からシークバイト位置を求める一例を示している。
【００３３】
図６において、通常、外部制御部３からのシーク指示はファイルの先頭の再生開始映像を０として時間情報で与えられるため（Ｓ３０１）、ＤＥＭＵＸ４は管理テーブル７を用いて以下のようにシークすべきＰＴＳ（ＤＴＳ）を計算する。
ＰＴＳ（ＤＴＳ）＝（Ｆｉｒｓｔ＿ＰＴＳ　＋　指示時間（秒）　／　９００００）　＆　０ｘ１ＦＦＦＦＦＦＦＦ
【００３４】
上記計算の結果、シークすべき時間と対応するバイト位置の情報が既に管理テーブル７に存在する場合は、直接そのバイト位置にシークして再生を開始する（Ｓ３０２、Ｓ３０６及び３０７）。再生開始後の制御フローは図５に示した通りである。
【００３５】
一方、上記計算の結果、シークすべき時間と対応するバイト位置の情報が管理テーブル７に存在しない場合は、次に計算された時刻の前後又は近傍に現在判明しているＧＯＰの時間とバイト位置が存在するか否かを判定する（Ｓ３０３）。存在しない場合には、該当する空間の「平均ビットレート」と「指示時間と判明しているＧＯＰ時間との差分」をかけて算出したバイト数とＧＯＰのバイト位置を演算することでシークすべきバイト位置を割り出す（Ｓ３０４）。
【００３６】
図１２の例でいえば、該当する空間の平均ビットレート　（２，６６６，６６６ｂｐｓ）　を用い、且つ計算したシーク時間が２０秒の場合は現在判明しているより近傍のＧＯＰ時間（１０秒）及びバイト位置（７，５００，１００ｂｙｔｅ）を用いて以下のようにシークすべきバイト位置を計算する。
７５００１００　＋　（２６６６６６６　＊　（２０−１０）／８）
【００３７】
一方、計算したシーク時間が８０秒の場合は、現在判明しているより近傍のＧＯＰ時間（１００秒）及びバイト位置　（３７，５００，１００ｂｙｔｅ）　を用いて以下のようにシークすべきバイト位置を計算する。
３７５００１００　−　（２６６６６６６　＊　（１００−８０）／８）
【００３８】
一方、計算された時刻の前後又は近傍に現在判明しているＧＯＰの時間とバイト位置が存在する場合は、さらに以下の点を考慮する（Ｓ３０３及び３０５）。すなわち、ＶＢＲでは、図３で示したようにシーンチェンジや動きの多い映像の場合は高ビットレートの符号化データとなり、動きの少ない映像の場合は低ビットレートとなる。
【００３９】
そのため、動きの変化点の前後を除くとシーク位置に対応するＧＯＰのバイト位置が管理テーブル７には登録されていないが、当該変化点の直前又は直後のミクロなＧＯＰ単位の平均ビットレートが管理テーブルに登録されている場合には、検索用の平均ビットレートを用いるよりも当該変化点の直前又は直後のＧＯＰ単位の平均ビットレートを用いるほうがシークの精度は向上する。
【００４０】
この場合には、ステップ３０４で用いた平均ビットレートに代えて、前記直前又は直後の平均ビットレートを用いてシークの位置に対応するＧＯＰを発見し、それによって管理テーブル７を更新する。図１３の例では、該当する変化点の直前のＧＯＰ単位の平均ビットレート　（２，６６６，６６６ｂｐｓ）　を用い、計算したシーク時間が１１．５秒の場合のシークすべきバイト位置を以下のように計算する。
７，８３３，４３２　＋　（２６６６６６６　＊　１０／８）
【００４１】
より近傍の平均ビットレートのほうが全体の平均ビットレートよりも正確であるため、この平均ビットレートを用いて正確なランダムアクセス可能なポイントを算出し、それによって蓄積データのサーチ量も削減され、高速な特殊再生が実現される。
【００４２】
このようなシークは、逆再生（ＭＰＥＧでは順方向にしか復号できないため、１ＧＯＰ前から１ＧＯＰ分復号し、逆順で映像を表示する）、高速再生（早送りのため全てのフレームを復号する必要はなく、例えばＧＯＰ毎のＩフレームのみを復号して表示する）、又は高速逆再生（早戻しも同様にＧＯＰ毎のＩフレームのみを復号して表示する）等、の１ＧＯＰ単位で検索する必要があるものに有効である。この場合、ＧＯＰ単位の時間は再生開示時に取得したものを用いることができる。
【００４３】
以降、該当バイト位置から順方向に蓄積データをサーチする（Ｓ３０８及び３０９）。ビデオパケットのＰＴＳ（ＤＴＳ）を発見した場合には、発見したＰＴＳ（ＤＴＳ）がシークすべきＰＴＳ（ＤＴＳ）より前で且つシークすべきＰＴＳ（ＤＴＳ）の基準範囲内にある場合に、そのまま蓄積データを順方向にサーチしてＧＯＰを検索する（Ｓ３１０〜３１３）。それ以外の場合は、発見したＰＴＳ（ＤＴＳ）とシークすべきＰＴＳ（ＤＴＳ）との時間差と平均ビットレートから再度シークすべきバイト位置を計算しなおす（Ｓ３１６）。
【００４４】
ＧＯＰを発見すると、そのＧＯＰの時間及びＧＯＰの蓄積データのバイト位置から前後のビットレートを算出し、これらの情報によって管理テーブル７を更新してから再生を開始する（Ｓ３１３〜３１５）。このようにして、シークに該当するバイト位置の検索と管理テーブル７の更新が行なわれていく。
【００４５】
上述した（１）〜（３）の各処理から明らかなように、本願発明では先ず（１）の処理で計算した平均ビットレートを、（２）及び（３）の各処理によって逐次修正していく。そのため、再生が進むにつれてより正確なランダムアクセス可能なポイントが算出でき且つ蓄積データのサーチ量も削減できるため、任意のＭＰＥＧ蓄積データに対して高速な特殊再生が実現される。
【００４６】
（４）管理テーブルの統合
図８には、管理テーブル７の統合化のための制御フロー例を示している。また、図１４には、管理テーブル７の統合化の一例を示している。
【００４７】
管理テーブル７に検出されたＧＯＰ毎のデータを順次保存していくと、長時間の蓄積ファイルの場合には膨大なテーブルが必要となる。そのため、図６では隣接する前後のＧＯＰ間のビットレートが同一ビットレートの場合に、それら複数のＧＯＰを一つに統合することで管理テーブル７の領域を削減する（Ｓ４０１及び４０２）。なお、厳密に同一ビットレートでなくても相互に近いビットレートであれば、複数のＧＯＰを統合することは可能である。
【００４８】
図１４には、互いに同じ平均ビットレート　（２，６６６，６６６ｂｐｓ）　をもつＧＯＰ時間１０秒とＧＯＰ時間１０．５秒とを統合して、ＧＯＰ時間１０．５秒のデータを削除した例を示している。このうち、削除したＧＯＰ時間１０．５秒のデータについては前述した計算式から正確に算出できる。
【００４９】
（５）ＧＯＰ単位の検索
図９には、シーク指示された時間をＧＯＰ単位に変換する制御フローの一例を示している。
図９では、先に（３）で説明したシーク指示の時間がＧＯＰ単位の時間と一致しない場合に、シーク指示された時間に一番近いＧＯＰ単位の時間を求める（Ｓ５０１及び５０２）。このように、ＧＯＰ単位のバイト位置の検索を行えば、検索バイト位置からスキャンする蓄積データ量を削減することが可能できる。
【００５０】
【発明の効果】
以上説明したように、本発明によれば、任意のＭＰＥＧ蓄積データを、インデックス情報やインデックスファイルのような外部情報を用いずに、特殊再生を行うためのＧＯＰのポイントを高速に且つ蓄積データ内のサーチ量が少なく正確に行なえる。
【００５１】
具体的には、ＭＰＥＧ蓄積データからのみデータの平均ビットレートを計算し、また蓄積ファイルの先頭及び最終部分のみサーチを行うため、再生開始時点でのサーチ量は少なく、インデックスファイルを作成するようなシステムよりも高速に再生が開始できる。
【００５２】
また、再生開始前に作成した平均ビットレートを再生の過程で逐次修正していくことで、再生が進むにつれてより正確なランダムアクセス可能なポイントが算出でき、それによって蓄積データのサーチ量が削減できて高速な特殊再生が実現できる。
【００５３】
さらに、より近傍の平均ビットレートのほうが全体の平均ビットレートよりも正確であるため、この平均ビットレートを用いることでより正確なランダムアクセス可能なポイントが算出でき、蓄積データのサーチ量を削減した高速な特殊再生が実現できる。
【００５４】
なお、本発明は蓄積ファイルがＶＢＲに限らずＣＢＲの場合にも適用可能である。ＣＢＲの場合には、管理テーブル上の平均ビットレートが各ＧＯＰ間で同一となるため管理テーブルに対する操作が冗長となるだけで、ＣＢＲ又はＶＢＲの蓄積ファイルの構造を意識することなく適用できる。
【図面の簡単な説明】
【図１】本発明によるＭＰＥＧデータの再生装置の一構成例を示した図である。
【図２】ＭＰＥＧデータフォーマットの一例を示した図である。
【図３】ＶＢＲにける映像データとビットレートとの関係を示した図である。
【図４】蓄積データの再生開始時における制御フローの一例を示した図である。
【図５】順方向再生時の制御フローの一例を示した図である。
【図６】シーク指示による制御フローの一例（１）を示した図である。
【図７】シーク指示による制御フローの一例（２）を示した図である。
【図８】管理テーブルの統合化の制御フロー例を示した図である。
【図９】シーク指示時間をＧＯＰ単位に変換する制御フローの一例を示した図である。
【図１０】再生開始時に作成される管理テーブルの一例を示した図である。
【図１１】順方向再生における管理テーブルの更新の一例を示した図である。
【図１２】管理テーブルからシークバイト位置を求める一例（１）を示した図である。
【図１３】管理テーブルからシークバイト位置を求める一例（２）を示した図である。
【図１４】管理テーブルの統合化の一例を示した図である。
【符号の説明】
１…ファイル
２…蓄積データ読み込み部
３…外部制御部
４…ＤＥＭＵＸ部
５…ＰＴＳ／ＤＴＳ検出部
６…ＧＯＰ検出部
７…管理テーブル
８…ビデオデコーダ
９…オーディオでコーダ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and apparatus for reproducing MPEG (Moving Picture Experts Group) data, and more particularly to reading and reproducing MPEG data stored at a variable bit rate (VBR) from an arbitrary position. The present invention relates to a random-accessible MPEG data reproduction method and apparatus for performing reverse reproduction, fast forward, or rewind.
[0002]
[Prior art]
At present, the price of the MPEG encoder has been reduced and the transfer of a large amount of data has become possible due to the speeding up of the LAN, so that the MPEG compression method is widely used. In the MPEG1 and MPEG2 systems, which are systems for compressing and storing moving images, the compression is performed on the premise that the moving image is reproduced in the forward direction of the time axis.
[0003]
For the compression, a method of compressing a moving image at a fixed bit rate (CBR: Constant Bit Rate) is used, and in a scene having a low compression efficiency to maintain the same image quality, the compression is performed at a high bit rate, and conversely, the compression efficiency is reduced. In a good scene, there is a variable bit rate compression method (VBR) that performs compression at a low bit rate.
[0004]
In the MPEG system, a GOP (Group of pictures) unit is defined as a point at which random access is possible. The first frame of the GOP starts with an I frame that can be decoded without reference to the front and rear frames, and P and B frames with the reference continue. Therefore, reproduction in the forward direction is possible from a GOP point. When an MPEG moving image is reproduced from an arbitrary point, reproduction is started from a GOP point near the point.
[0005]
In the case of an MPEG file stored in CBR, since the GOP point is determined by a fixed bit rate and the number of frames in the GOP, the GOP point can be searched by simple calculation. On the other hand, in the case of an MPEG file stored in VBR, it is not easy to search for a GOP point because the size of the GOP changes for each GOP.
[0006]
For this reason, with respect to arbitrary stored data to which a GOP point is not added as index information or the like, for example, VBR MPEG data downloaded via a network, the stored data is used to know the GOP point. All are scanned and GOP points are created as separate information such as an index file. Thereafter, by performing a seek using the created information, a special reproduction operation other than the forward reproduction from the head data is supported.
[0007]
[Problems to be solved by the invention]
As described above, when performing special reproduction of arbitrary MPEG stored data, especially MPEG stored data by VBR, an index file or the like is created before reproduction, so that stored data having a high average bit rate or long-time stored data is generated. In such a case, there is a problem that it takes time to start the reproduction.
[0008]
In view of the above problems, it is an object of the present invention to calculate an average bit rate and predict an access point to be searched for a non-reproduced portion when reproducing arbitrary MPEG stored data, As for, by using the GOP point value detected at the time of the reproduction and dynamically updating the prediction data at the time of the special reproduction by the GOP point value, the search accuracy of the random access point in the reproduction process of arbitrary MPEG accumulated data is improved. It is an object of the present invention to provide a method and an apparatus for reproducing MPEG data which are configured to improve at any time. This makes it possible to perform high-speed and accurate random access point search regardless of the file structure such as the difference between CBR and VBR and the presence or absence of an index file.
[0009]
[Means for Solving the Problems]
According to the present invention, the average bit rate calculated from the head and the last time information of the accumulated moving image data is stored in a table, and a random accessible image group at the head of the moving image data and the last image group of the moving image data are stored. Detecting and storing time information and position information, further calculating the image group unit time based on the number of frames between the adjacent image groups and storing the calculated time in the table, the average bit rate stored in the table, Calculating the point to be accessed based on the time information and position information of the image group, and the image group unit time, starting the reproduction from the calculated point to be accessed and detecting the point in the reproduction process Time information and position information of the image group, and each image calculated based on the information. The average bit rate between the loops, it will save the table, the method of reproducing video data consisting of are provided.
[0010]
Further, according to the present invention, there is provided a moving image data reproducing apparatus for reproducing accumulated moving image data, wherein a means for extracting head information and last time information of the moving image data and calculating an average bit rate for search, Means for starting playback from an access point calculated using the average bit rate for the search, means for storing predetermined playback information of the moving image data detected in the course of the playback, and Means for correcting the average bit rate for the search with the reproduction information of the completed part.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows an example of the configuration of an apparatus for reproducing MPEG data according to the present invention.
In FIG. 1, a file 1 includes an auxiliary storage device such as a hard disk, and stores MPEG data such as MPEG1 and MPEG2-PS downloaded via a network. The external control unit 3 gives to the DEMUX unit 4 an image to be reproduced specified by the user and an instruction for a special reproduction thereof. The stored data reading unit 2 reads part or all of the MPEG data stored in the file 1 under the control of the DEMUX unit 4 and transfers the data to the DEMUX unit 4.
[0012]
The DEMUX unit 4 captures MPEG data to be normally reproduced or specially reproduced through the stored data reading unit 2 according to an instruction from the external control unit 3, and separates the MPEG data into MPEG video data and MPEG audio data. The separated MPEG video data is output to a video decoder 8 and the MPEG audio data is output to an audio decoder 9.
[0013]
The video decoder 8 performs a decoding process such as an inverse DCT transform on the received MPEG video data, and outputs video data restored thereby. The audio decoder 9 also performs similar decoding processing on the MPEG audio data and outputs the restored audio data.
[0014]
The above configuration is the same as that of a normal MPEG data reproducing apparatus, but the present invention further includes the following configuration. That is, the DEMUX unit 4 is provided with a PTS / DTS detection unit 5 and a GOP detection unit 6, and the DEMUX unit 4 is further provided with a management table 7. Here, before describing the PTS / DTS detection unit 5, the GOP detection unit 6, and the management table 7, an outline of MPEG data related to them will be described.
[0015]
FIG. 2 shows an example of the MPEG data format. FIG. 3 shows the relationship between video data and bit rate in VBR.
In FIG. 2, (a) of FIG. 2 shows an example of the data format of MPEG1-SYSTEM or MPEG2-PS (Program Stream), which starts with the first pack header and ends with an end code (not shown). A pack is generally composed of a plurality of packets, and the first pack header includes an identification code "00" of MPEG1-SYSTEM or an identification code "01" of MPEG2-PS.
[0016]
The system header describes the parameters of the entire stream. The rate_bound field contains the bit rate, and the other fields contain various parameters such as the number of video channels and the number of audio channels. Also, each packet header of the video packet and the audio packet includes parameters such as PTS (Presentation Time Stamp) which is time management information of reproduction output and DTS (Decoding Time Stamp) which is time management information of decoding. It is composed of a cyclic counter of bits, and can manage time of up to about 26 hours.
[0017]
FIG. 2B shows an example of the VBR video stream size. As described above, the GOP (Group of pictures) has a screen structure including at least one intra-frame coded screen (I frame) in order to enable random access. One GOP is composed of a sequence header and a GOP part. The GOP part includes a plurality of B and P frames including at least one I frame, and is usually grouped in about 0.5 seconds (15 frames). You.
[0018]
In the case of VBR, since the GOP size varies depending on the magnitude of the motion of the video, the bit rate is varied as shown by the solid line in FIG. As shown by the dotted line in FIG. 3, in the case of CBR, the maximum bit rate is fixedly set, and dummy data (padding data) is inserted in the low bit rate data to keep the GOP size constant.
[0019]
Referring back to FIG. 1 with reference to the above, the PTS / DTS detection unit 5 detects PTS (DTS) information in each packet header of a video packet. The GOP detection unit 6 performs detection in GOP units that can be accessed randomly. The management table 7 is a data table that is added, changed, and updated as needed during normal playback and special playback based on information detected by the PTS / DTS detection unit 5 and the GOP detection unit 6.
[0020]
Hereinafter, an embodiment of the present invention will be described with reference to an example of a management table in FIGS.
(1) Start of Playback of Stored Data FIG. 4 shows an example of a control flow at the start of playback of stored data. FIG. 10 shows an example of a reproduction management table created first when reproduction of stored data is started.
[0021]
The DEMUX 4 first controls the stored data reading unit 2 to read the head portion of the corresponding MPEG file from the file 1 in response to a predetermined MPEG file reproduction instruction from the external control unit 3, and fetches the contents of rate_bound in the system header, Then, the maximum bit rate of the stored data is calculated (S101). The calculated maximum bit rate (6 Mbps in this example) is stored in the special reproduction management table as an upper limit rate during reproduction (FIG. 10).
[0022]
Next, the PTS or DTS of the GOP in the video packet at the head of the file is captured, and the byte position thereof is also captured (S102). Furthermore, the PTS or DTS of the GOP in the second video packet from the head of the file is fetched, and its byte position is also fetched. One GOP time is calculated from the number of frames between these two GOPs, and this value (0.5 seconds in this example) is also stored in the special reproduction management table (S103).
[0023]
In general, in MPEG stored data regardless of CBR / VBR, the data amount for each GOP varies but the number of frames in one GOP is the same, so that the time unit for each GOP often does not change. Therefore, the time information of one GOP is also effective information for special reproduction. The above-mentioned maximum bit rate and one GOP time are stored as fixed values, and are not changed or updated thereafter.
[0024]
Finally, scanning is started from the return position of the maximum bit rate × α (the time for capturing the final GOP) from the end of the file, and the PTS or DTS of the last GOP of the video packet and its byte position are captured (S104). . From this information and the information of the first GOP obtained earlier, the total file reproduction time is calculated as follows (S105).
[0025]
Here, the maximum bit rate is Max_Bit_Rate, the first PTS (DTS) is First_PTS, the first byte position is First_Byte, the last PTS (DTS) is Last_PTS, the last byte position is Last_Byte, and the total playback time is Total_Time. Since the PTS (DTS) is a 33-bit cyclic counter in units of 90 KHz, the total playback time can be described by the following equation. Note that the following equation can also calculate a time exceeding a maximum of 26 hours that can be specified by 33 bits.
[0026]

[0027]
FIG. 10 shows an example in which the average bit rate (4 Mbps in this example) is calculated from the byte size (total number of bytes) of the file using the total playback time calculated by the above equation. From this, the GOP time and byte position of each of the first GOP and the last GOP, and the average bit rate between the first GOP and the last GOP are obtained. As described above, by acquiring the minimum information necessary for reproducing the file before the reproduction is started, the initial management table 7 for performing the special reproduction of the MPEG file is created (S106).
[0028]
According to the present invention, since the average bit rate of data is calculated only from the MPEG accumulated data, and only the beginning and the end of the accumulated file need to be searched, the search amount at the start of reproduction is small, and a conventional index file is created. Playback is started faster than such a system.
[0029]
(2) In the case of reproducing in the forward direction from the beginning FIG. 5 shows an example of a control flow at the time of reproducing in the forward direction. FIG. 11 shows an example of updating the management table 7 in forward reproduction.
[0030]
The DEMUX 4 controls the stored data reading unit 2 according to a forward reproduction instruction from the external control unit 3 to sequentially read a series of stored data for decoding and reproduction (S201). In the decoding / reproducing process (S204), the bit rate for each GOP is calculated from the actually detected time for each GOP and the byte position of the stored data for each GOP, and the contents of the management table 7 are stored and updated based on the information. (S202 and S203).
[0031]
In the example of FIG. 11, the second, third,..., Time for each GOP, the byte position for each GOP, and the time for each GOP calculated based on the information detected by the GOP detection unit 6 in the forward reproduction process. The average bit rate is inserted and stored between the first GOP and the last GOP.
[0032]
(3) When a seek instruction is issued at a time when the byte position of the GOP is not registered in the management table FIGS. 6 and 7 show an example of a control flow according to the seek instruction. 12 and 13 show an example of obtaining a seek byte position from the management table 7.
[0033]
In FIG. 6, normally, a seek instruction from the external control unit 3 is given as time information with the playback start video at the beginning of the file being 0 (S301), so that the DEMUX 4 should seek using the management table 7 as follows. Calculate PTS (DTS).
PTS (DTS) = (First_PTS + instruction time (sec) / 90000) & 0x1FFFFFFFF
[0034]
As a result of the calculation, if the information of the byte position corresponding to the time to be sought already exists in the management table 7, the seek is directly performed to the byte position and the reproduction is started (S302, S306 and 307). The control flow after the start of the reproduction is as shown in FIG.
[0035]
On the other hand, as a result of the above calculation, when the information of the byte position corresponding to the time to be sought is not present in the management table 7, the time and the byte position of the GOP currently known before, after, or near the next calculated time are calculated. It is determined whether or not exists (S303). If not, seek should be performed by calculating the number of bytes calculated by multiplying the "average bit rate" of the corresponding space by the "difference between the indicated time and the GOP time" and the byte position of the GOP. The byte position is determined (S304).
[0036]
In the example of FIG. 12, when the average bit rate (2,666, 666 bps) of the corresponding space is used and the calculated seek time is 20 seconds, a GOP time (10 seconds) closer to the presently known value is obtained. And the byte position (7,500,100 bytes) is used to calculate the byte position to seek.
7500100 + (26666666 * (20-10) / 8)
[0037]
On the other hand, if the calculated seek time is 80 seconds, the byte position to be sought is determined as follows using the currently known GOP time (100 seconds) and the byte position (37,500,100 bytes). calculate.
37500100-(2666666 * (100-80) / 8)
[0038]
On the other hand, if the currently known GOP time and byte position exist before, after, or near the calculated time, the following points are further considered (S303 and 305). That is, in the case of VBR, encoded data of a high bit rate is obtained in the case of a scene change or a video with a lot of motion as shown in FIG.
[0039]
Therefore, the byte position of the GOP corresponding to the seek position is not registered in the management table 7 except before and after the change point of the movement, but the average bit rate of the micro GOP unit immediately before or immediately after the change point is managed. When registered in the table, seek accuracy is improved by using the average bit rate in GOP units immediately before or immediately after the change point, rather than using the average bit rate for search.
[0040]
In this case, the GOP corresponding to the seek position is found using the immediately preceding or following average bit rate instead of the average bit rate used in step 304, and the management table 7 is updated accordingly. In the example of FIG. 13, using the average bit rate (2,666,666 bps) in GOP units immediately before the corresponding change point, the byte position to be sought when the calculated seek time is 11.5 seconds is as follows. To calculate.
7,833,432 + (266666 * 10/8)
[0041]
Since the closer average bit rate is more accurate than the overall average bit rate, an accurate random accessible point is calculated using this average bit rate, thereby reducing the amount of search for stored data, and Special reproduction is realized.
[0042]
Such a seek can be performed in reverse playback (MPEG can only decode in the forward direction, so decoding is performed for one GOP before one GOP, and the video is displayed in reverse order), high-speed playback (there is no need to decode all frames for fast-forwarding). For example, it is necessary to search in units of one GOP such as, for example, decoding and displaying only the I frame of each GOP) or high-speed reverse reproduction (similarly to fast reverse, decoding and displaying only the I frame of each GOP). Effective for things. In this case, the time obtained in GOP unit at the time of starting the reproduction can be used.
[0043]
Thereafter, the stored data is searched from the corresponding byte position in the forward direction (S308 and 309). When the PTS (DTS) of the video packet is found, if the found PTS (DTS) is before the PTS (DTS) to be sought and is within the reference range of the PTS (DTS) to be sought, it is stored as it is. A GOP is searched by searching data in the forward direction (S310 to 313). In other cases, the byte position to be sought again is calculated from the time difference between the found PTS (DTS) and the PTS (DTS) to be sought and the average bit rate (S316).
[0044]
When the GOP is found, the preceding and succeeding bit rates are calculated from the time of the GOP and the byte position of the stored data of the GOP, and the management table 7 is updated with these pieces of information, and then the reproduction is started (S313 to 315). In this way, the search of the byte position corresponding to the seek and the update of the management table 7 are performed.
[0045]
As is clear from the processes (1) to (3) described above, according to the present invention, the average bit rate calculated in the process (1) is first corrected sequentially by the processes (2) and (3). Go. As a result, more accurate random access points can be calculated as the reproduction progresses, and the amount of search for the stored data can be reduced. As a result, high-speed special reproduction of arbitrary MPEG stored data is realized.
[0046]
(4) Integration of Management Table FIG. 8 shows an example of a control flow for integrating the management table 7. FIG. 14 shows an example of integration of the management table 7.
[0047]
If the detected data for each GOP is sequentially stored in the management table 7, an enormous table is required for a long-time accumulated file. Therefore, in FIG. 6, when the bit rates between adjacent GOPs are the same, the area of the management table 7 is reduced by integrating the plurality of GOPs into one (S401 and 402). A plurality of GOPs can be integrated as long as the bit rates are not exactly the same but are close to each other.
[0048]
FIG. 14 shows an example in which a GOP time of 10 seconds and a GOP time of 10.5 seconds having the same average bit rate (2,666,666 bps) are integrated and data of the GOP time of 10.5 seconds is deleted. ing. Among them, the deleted data of the GOP time of 10.5 seconds can be accurately calculated from the above-mentioned formula.
[0049]
(5) Search in GOP Unit FIG. 9 shows an example of a control flow for converting a time instructed to seek into a GOP unit.
In FIG. 9, when the seek instruction time described in (3) does not coincide with the GOP unit time, the GOP unit time closest to the seek instruction time is obtained (S501 and 502). As described above, if the search for the byte position in GOP units is performed, the amount of accumulated data scanned from the search byte position can be reduced.
[0050]
【The invention's effect】
As described above, according to the present invention, a point of a GOP for performing special reproduction can be set at a high speed and within the stored data without using any external information such as index information or an index file. The search amount is small and accurate.
[0051]
More specifically, since the average bit rate of data is calculated only from the MPEG stored data and only the beginning and end of the stored file are searched, the amount of search at the start of reproduction is small, and an index file is created. Playback can be started faster than the system.
[0052]
Also, by sequentially correcting the average bit rate created before the start of playback in the course of playback, more accurate random access points can be calculated as playback progresses, thereby reducing the amount of search for stored data. And high-speed special reproduction can be realized.
[0053]
Further, since the average bit rate in the vicinity is more accurate than the average bit rate of the whole, more accurate random access points can be calculated by using the average bit rate, and the search amount of the stored data is reduced. High-speed special reproduction can be realized.
[0054]
The present invention is applicable not only to the case where the storage file is VBR, but also to the case where the storage file is CBR. In the case of CBR, the average bit rate on the management table is the same between the GOPs, so that the operation on the management table is only redundant, and can be applied without being aware of the structure of the CBR or VBR storage file.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration example of an MPEG data reproducing apparatus according to the present invention.
FIG. 2 is a diagram showing an example of an MPEG data format.
FIG. 3 is a diagram showing a relationship between video data and a bit rate in VBR.
FIG. 4 is a diagram showing an example of a control flow at the start of reproduction of stored data.
FIG. 5 is a diagram showing an example of a control flow at the time of forward reproduction.
FIG. 6 is a diagram illustrating an example (1) of a control flow according to a seek instruction;
FIG. 7 is a diagram illustrating an example (2) of a control flow according to a seek instruction;
FIG. 8 is a diagram illustrating an example of a control flow for integrating management tables.
FIG. 9 is a diagram illustrating an example of a control flow for converting a seek instruction time into GOP units.
FIG. 10 is a diagram showing an example of a management table created at the start of reproduction.
FIG. 11 is a diagram showing an example of updating a management table in forward reproduction.
FIG. 12 is a diagram illustrating an example (1) of obtaining a seek byte position from a management table;
FIG. 13 is a diagram showing an example (2) of obtaining a seek byte position from a management table.
FIG. 14 is a diagram showing an example of integration of management tables.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... File 2 ... Storage data reading part 3 ... External control part 4 ... DEMUX part 5 ... PTS / DTS detecting part 6 ... GOP detecting part 7 ... Management table 8 ... Video decoder 9 ... Audio coder

Claims (5)

Storing the average bit rate calculated from the start and end time information of the accumulated video data in a table,
Detect and save time information and position information of the first randomly accessible image group and the last image group of the moving image data, and calculate the image group unit time based on the number of frames between adjacent image groups. To store in the table,
Calculating an average bit rate stored in the table, time information and position information of the image group, and points to be accessed based on the image group unit time;
Playback is started after the calculated point to be accessed, and the time information and position information of the image groups detected in the playback process, and the average bit rate between each image group calculated based on the information. Is stored in the table. 2. The moving image data reproducing method according to claim 1, further comprising: correcting an average bit rate of a non-reproduced portion to be accessed based on the stored time information, byte position, and average bit rate of the image group of the reproduced portion. 3. The moving image data reproducing method according to claim 2, further comprising using an average bit rate of the reproduced portion when the non-reproduced portion is near the reproduced portion. The moving image data according to any one of claims 1 to 3, further comprising reducing redundant information that can be calculated from time information, position information, and an average bit rate of each image group stored in the table. How to play. A video data playback device that plays back the stored video data,
Means for extracting the top and last time information of the video data and calculating an average bit rate for search;
Means for starting playback from an access point calculated using the average bit rate for the search,
Means for storing predetermined reproduction information of the moving image data detected in the reproduction process,
Means for correcting the average bit rate for the search by the stored reproduction information of the reproduced portion,
An apparatus for reproducing moving image data, comprising:

Images