243:, encoders have much more flexibility about referencing structures. They can use the same referencing structures as were previously used in older designs, or they can use more pictures as references and they can use more flexible ordering of the coding order relative to the display order. They are also allowed to use B frames as references when coding other (B or P) frames. This extra flexibility can improve compression efficiency, but it can cause propagation of errors if some data becomes lost or corrupted. One popular structure for use with the newer designs is the use of a hierarchy of B frames. Hierarchical B frames can provide very good compression efficiency and can also limit the propagation of errors, since the hierarchy can ensure that the number of pictures affected by any data corruption problem is strictly limited.
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206:(bipredictive coded picture) – contains motion-compensated difference information relative to previously decoded pictures. In older designs such as MPEG-1 and H.262/MPEG-2, each B frame can only reference two frames, the one which precedes the B frame in display order and the one which follows, and all referenced pictures must be I or P frames. These constraints do not apply in newer standards
265:. The first number tells the distance between two anchor frames (I or P), also known as the length of a "mini-GOP". The second one tells the distance between two full images (I-frames): it is the GOP size. Instead of the M parameter, the maximal count of B-frames between two consecutive anchor frames can be used; this is the approach used by
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an "open GOP". The opposite is a self-contained GOP, known as a "closed GOP". In coding order GOP can begin with a B-frame, but it cannot end with one. Open GOP starts with a B-frame and it is a little more efficient because starting with an I-frame means that an extra P-frame must be added to the end (a GOP cannot end with a B-frame).
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IDR frame (Instantaneous
Decoder Refresh): I frame with a marking indicating that no subsequent P frames have references reaching further back than this I frame. Through the use of these IDR frames, closed GOPs are formed that can’t refer to frames outside the GOP. IDR are the true keyframes together
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With H.264 and later designs which allow highly flexible reference structures, a B frame in one GOP is able to reference a frame in a different GOP, in particular even before the I frame, which makes I frame non-IDR (not a keyframe). A GOP that contains any such outward-referencing frame is known as
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are arranged. The GOP is a collection of successive pictures within a coded video stream. Each coded video stream consists of successive GOPs, from which the visible frames are generated. Encountering a new GOP in a compressed video stream means that the decoder doesn't need any previous frames in
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The I frames contain the full image and do not require any additional information to reconstruct them. Typically, encoders use GOP structures that cause each I frame to be a "clean random access point," such that decoding can start cleanly on an I frame and any errors within the GOP structure are
214:. Sometimes, a codec will use unidirectional B-frames. This is a P-frame that, while it does not use data from a future frame, no other frames depend on it. A fundamental property of B-frames is that they can be dropped without affecting the correct decoding of other frames.
192:, each P frame can only reference one picture, and that picture must precede the P frame in display order as well as in decoding order, and the reference must be an I or P frame. These constraints do not apply in the newer standards
160:(intra coded picture, also sometimes incorrectly called keyframe) – a picture that is coded independently of all other pictures. Each GOP begins (in decoding order) with this type of frame.
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An I frame indicates the beginning of a GOP. Afterwards, several P and B frames follow. In older designs, the allowed ordering and referencing structure is relatively constrained.
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Generally, the more I frames the video stream has, the more editable it is. However, having more I frames substantially increases bit rate needed to code the video.
220:(DC direct coded picture) – serves as a fast-access representation of a frame for loss robustness or fast-forward. D frames are only used in
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525:"Docs/Appendix-Adaptive-Prediction-Structure.md · master · Alliance for Open Media / SVT-AV1 · GitLab"
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to insert an I-frame on scene change is a well-known technique. Newer techniques also vary
495:"Adaptive Intra-Frame Assignment and Bit-Rate Estimation for Variable GOP Length in H.264"
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difference information relative to previously decoded pictures. In older designs such as
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bf integer (encoding,video) Set max number of B frames between non-B-frames.
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order to decode the next ones, and allows fast seeking through the video.
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The GOP structure is often referred by two numbers, for example,
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IEEE Transactions on
Circuits and Systems for Video Technology
442:"Closed GOP and Open GOP - Simplified Explanation - OTTVerse"
312:. There are 4 B-frames between two consecutive anchor frames.
291:. There are 2 B-frames between two consecutive anchor frames.
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543:"Broken frames due to H.264 Open-GOP (DVB MPEG-TS) ?"
420:"Hierarchical B-Frames or B-Pyramid - Video Compression"
382:"What is "Group Of Pictures" and Why is it Important?"
46:. Unsourced material may be challenged and removed.
164:with clean random access frames (recovery points).
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367:"Keyframes, InterFrame & Video Compression"
153:A GOP can contain the following picture types:
232:corrected after processing a correct I frame.
440:Vijayanagar, Krishna Rao (17 December 2020).
324:based on the amount of motion in the video.
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106:Learn how and when to remove this message
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172:(predictive coded picture) – contains
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44:adding citations to reliable sources
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505:(10): 1271–1279. October 2006.
380:McCarrel, Jarrod (2022-05-04).
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460:"Compressor 4 User Manual"
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511:10.1109/TCSVT.2006.881856
287:, the GOP structure is
40:improve this article
386:Venera Technologies
328:Additional concepts
55:"Group of pictures"
305:, anchor-distance
174:motion-compensated
601:Video compression
531:. 23 August 2023.
424:www.ramugedia.com
294:For the sequence
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574:. Retrieved
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478:ffmpeg.org
406:"B-Frames"
391:2024-06-22
354:References
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348:Key frame
250:Structure
96:July 2013
337:See also
143:Elements
218:D frame
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