^ ab B-frames are not natively supported so bitstream processing or "packing" is needed. Details on this can be found in MPEG-4 B-frames in AVI/VFW description.
^ACM cannot handle VBR audio streams in AVI files. Thus, software using ACM to read audio from AVI files will not be able to handle VBR audio streams correctly, even though such files are compliant to the AVI file specification. This is a limitation of the ACM, not of the AVI file format.
^ Although AVI is not designed for variable framerates, it is possible to use them without creating a non-standard file by using 0-byte chunks for skipped frames. However it requires framerate to be set to Least common multiple of all framerates used, and produces slight overhead compared to true VFR.
^ ab Through an updated x264/ffdshow filter it is possible to view H.264 in an AVI file.
^ Although FFmpeg has introduced a solution to put Vorbis audio into AVI files, this "extension" is not compatible with existing Vorbis decoders for DirectShow and ACM. Putting Vorbis in an AVI container is very problematic. The way Nandub stored Vorbis audio streams in AVI files occasionally caused desychronisation when seeking.
^ The Matroska specs are put into the public domain, which means they are patent free and owned by everybody. The relevant, valid format specification is always the one found on matroska.org, the official homepage. Even if the Matroska specs are free, the code of the software tools for Matroska files can, nevertheless, be proprietary or follow a specific license (BSDL, GPL, LGPL, QPL, etc.), depending on the intentions of the programmer or the company behind them.
^ Possible, but not implemented at this date. The developers are awaiting the release of Musepack 8.x, as this version will completely change the bitstream.
^ As specified by SMPTE Recommended Practices 2025–2007, "VC-1 Bitstream Storage in the ISO Base Media File Format."
