This helps especially whenever there are fades, where the subsequent picture is very similar to the previous one except that it is darker. With Weigthed Prediction there can be weights applied to a reference frame (eg you can scale (brightness-wise) a previous picture).
Allowing multiple reference frames will slow down encoding and decoding and cutting will be only possible at IDR-Frames Because of that (eg a P-Frame can refer to a frame before the latest I-Frame) a new frametype had to be introduced: IDR-Frames, which are I-Frames before which no following frame is allowed to refer to. In contrary to MPEG-4 ASP (which only allows using the frame before the actual frame as reference), AVC/H.264 offers choosing from multiple ones for inter motion search, which means the codec can decide whether he wants to simply refer to the previous frame (like in ASP) or even to a frame before that. The Block Size is adaptive/variable, a good encoder will be smart enough to decide which one is best to use in every specific macroblock In contrary to MPEG-4 ASP (where, only with Inter4V/4MV, the Block Sizes can varry between 16x16 and 8x8 pixels), AVC/H.264 offers for Motion Search Precision the division of a macroblock down to 4x4 pixels (including steps like 8x4.).
Variable Block Sizes/Macroblock Partitions: This helps avoiding blocking artifacts, especially on low bitrates, but will slow down en/decoding In contrary to prefiltering (for example via avisynth, done on the input), or postprocessing/filtering (via the decoder, done on the final output), LoopFiltering is applied during the encoding process on every single frame, after it got encoded, but before it gets used as reference for the following frames. CABAC (as CAVLC) is a lossless method and therefore will never hurt the quality, but will slow down encoding and decoding. It seems the most usable profile for DVD Backups is the High Profile with maybe the following tools (also check out the tool description of MPEG-4 ASP as all, except GMC, are available in AVC too):ĪVC/H.264 defines two, more advanced tools for entropy coding of the bitstream syntax (macroblock-type, motionvectors + reference-index.) than MPEG-4 ASP: Context-Adaptive Variable Length Coding (CAVLC) and Context-Adaptive Binary Arithmetic Coding (CABAC)ĬABAC, compared to CAVLC (aka UVLC) which is the default method in AVC/H.264, is a more powerful compression method, being said to bring down the bitrate additonally by about 10-15% (especially on high bitrates). High Profile (aka FRExt) adds to Main Profile: 8x8 intra prediction, custom quants, lossless video coding, more yuv formats (4:4:4.) Main Profile offers I/P/B-Frames, supports progressive and interlaced, and offers CAVLC or CABAC Extended Profile offers I/P/B/SP/SI-Frames, supports progressive and CAVLC only Baseline Profile offers I/P-Frames, supports progressive and CAVLC only The AVC/H.264 standard defines four different Profiles: Baseline, Main, Extended and High Profile (which themselves are subdivided into Levels): Looking from the MPEG side the standard is called MPEG-4 Part 10 (ISO 14496-10), looking from the ITU side, it is called H.264 (the ITU document number), by which the format is widely known alreadyĪs "official" title for the new standard Advanced Video Coding (AVC) was chosen by MPEG - as video counterpart to the Advanced Audio Coding (AAC) audio format The AVC/H.264 Standard itself was developed by the Joint Video Team (JVT), which included experts from both MPEG and VCEG
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The AVC/H.264 Video Coding Standard was together finalized and identically specified in 2003 by two Groups, the MPEG (Moving Pictures Experts Group) from ISO and the VCEG (Video Coding Experts Group) from ITU (International Telecommunication Union), a suborganisation of the United Nations (UNO), which also standardised the H.263 format (mainly used in video conference software now) With AVC/H.264 the MPEG-4 Standard defines one of the newest and technically best available, state-of-the-art Video Coding Formats
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