Hello, there are currently a few open track issues related to Matroska attached pics: #2270, #4286, #4591 and #7717. So I thought it worthwhile to take a look.
The modifications to mux streams with disposition AV_DISPOSITION_ATTACHED_PIC that contain an attached pic are easy; see the second patch. Unfortunately, not every stream with this disposition has actually an attached pic, although the documentation says that the picture "can also be accessed at any time in AVStream.attached_pic." E.g. no output track in FFmpeg currently contains an attached pic; attached pics are not propagated from input streams. The first commit changes this a bit and together these two commits are enough to make remuxing attached pics from Matroska to Matroska with FFmpeg easily possible. It is also possible to use attached pics provided that they emanate from a demuxer that sets the attached_pic and provided one provides the necessary filename metadata information which containers other than Matroska don't provide on their own. But e.g. the scenario from #4286 doesn't work because just setting the disposition to attached pic doesn't fill the attached_pic. Therefore video tracks without attached_pic are always treated as a normal video track as they are now. There is also another complication: Actually, the description of attached_pic contains: "decoding: set by libavformat, must not be modified by the caller." This means that my patch to ffmpeg.c is unacceptable, isn't it? And it means that an API function to set the attached pic is required. I have not even looked into the complications that would arise if one wants to do more than a simple streamcopy. Finally, I am also wondering about how timed thumbnails should be handled: For a track that ends up as an attachment all the normal packets are discarded. Which is bad for timed thumbnails. - Andreas PS: There is btw another bug wrt to the video streams corresponding to attached pics: If they are muxed, the whole file is read until a packet from this stream is found; often this means that the file is read until the end. This is not Matroska-specific and probably caused by such streams being counted among the streams to interleave. Andreas Rheinhardt (2): fftools/ffmpeg: Propagate attached_pic avformat/matroskaenc: Write attached_pic as attachment fftools/ffmpeg.c | 8 ++++++++ libavformat/matroskaenc.c | 27 +++++++++++++++++++++------ 2 files changed, 29 insertions(+), 6 deletions(-) -- 2.19.2 _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
