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The quality the codec can achieve is heavily based on the compression format the codec uses. A codec is not a format, and there may be multiple codecs that implement the same compression specification – for example, MPEG-1 codecs typically do not achieve quality/size ratio comparable to codecs that implement the more modern H.264 specification.
MPEG-4 AVC (H.264) Lossy or lossless: August 2004 Patent encumbered [57] Yes Yes Yes Yes Yes [III] Yes Yes [58] Yes AV1: Lossy or lossless: March 2018 Patent claims Yes [59] [60] Yes No No No No Planned No VP9: Lossy or lossless: June 2013 Patent claims Yes Yes No Yes Yes No No No VP8: Lossy or lossless: September 2008 Patent claims Yes Yes No ...
The bit rate reductions for HEVC were determined based on PSNR with HEVC having a bit rate reduction of 35.4% compared with H.264/MPEG-4 AVC HP, 63.7% compared with MPEG-4 ASP, 65.1% compared with H.263 HLP, and 70.8% compared with H.262/MPEG-2 MP. [121] HEVC MP has also been compared with H.264/MPEG-4 AVC HP for subjective video quality.
x265 builds on source code from x264, an open-source video encoder for the previous MPEG video coding standard, H.264/MPEG-4 AVC. The project has licensed the rights to use the x264 source code. [3] Development on x265 began in March 2013. [7] MulticoreWare made the source code for x265 publicly available on July 23, 2013. [4] [5]
The H.264 specification calls H.261, H.262, H.263, and H.264 video coding standards and does not contain the word codec. [2] The Alliance for Open Media clearly distinguishes between the AV1 video coding format and the accompanying codec they are developing, but calls the video coding format itself a video codec specification. [3]
The HEVC standard defines thirteen levels. [1] [2] A level is a set of constraints for a bitstream.[1] [2] For levels below level 4 only the Main tier is allowed.[1] [2] A decoder that conforms to a given tier/level is required to be capable of decoding all bitstreams that are encoded for that tier/level and for all lower tiers/levels.
H.264 lossless x264 (encoder only) FFmpeg (decoder only, uses x264 for encoding) H.265 lossless [41] x265 (encoder only) UHDcode (decoder only, uses x265 to read HEVC encoded files) [42] FFmpeg (decoder only, uses x265 for encoding) [43] [44] Motion JPEG 2000 lossless libopenjpeg; JPEG XS lossless FastTICO-XS; IETF standards:
A CTU can be between 16×16 pixels and 64×64 pixels in size with a larger size usually increasing coding efficiency. [ 4 ] [ 2 ] The first video standard that uses CTUs is HEVC/H.265 which became an ITU-T standard on April 13, 2013.