Hi attached patch would change nut.txt to the alternative keyframe definition this would allow files with no classic keyframes but instead things like P frames where each would have 10% intra blocks to be muxed in nut and still allow seeking without this seeking is not possible, the seek to non keyframe hack would only work if all streams would allow seeking to any frame as back ptrs would not be meaningfull in such a file it would also fix cases where B frames with a PTS after the previous I frame would use frames prior to the I frame for prediction and it could be used to allow decoding B frames with a PTS prior to the last I frame, that is IPBBIBB ^^ if they dont use previous frames for prediction this would fix a missing feature relative to mpeg1/2/4 which allow that and provide enough information to make this odd case easily detectable Compatibility effects: new demuxers can always demux old files old demuxers can demux new files as long as they only contain normal keyframes otherwise they fail to demux the specific keyframes Effects on optimal seeking: unknown -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB No human being will ever know the Truth, for even if they happen to say it by chance, they would not even known they had done so. -- Xenophanes