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• Determine FFmpeg codecs available for container

  19 juillet 2020, par CasualDemon

  I am looking to generate lists of supported video / audio / subtitle tracks for each type of container in a particular build of FFmpeg.

  


  For example, I want to avoid errors like Could not find tag for codec <> in stream #0, codec not currently supported in container

  


  I know I can list available codecs with ffmpeg -codecs, and find details about a muxer with ffmpeg -h muxer=<muxer></muxer> like ffmpeg -h muxer=matroska but that will only show default codecs, not all possible.

  


  Muxer matroska [Matroska]:
    Common extensions: mkv.
    Mime type: video/x-matroska.
    Default video codec: h264.
    Default audio codec: vorbis.
    Default subtitle codec: ass.


  


  Basically I want to run this command across all available muxers to build up a table like wikipedia's format comparison charts that is FFmpeg build specific. This is designed to go in a program that wraps around FFmpeg, and I need to know which formats are valid for each container / file extension per FFmpeg build.

  


  Thanks !

  


• Transcode to ogg or webm, writing the file as it goes

  22 juillet 2020, par Mark Smith

  I need to transcode files (mp3, flac, m4a and others) to ogg or webm. (This is because I need them to play on Firefox 60.9 which does not support most of these, and flacs are too large. I cannot update the browser.)

  


  ffmpeg can do the transcoding, but when transcoding to ogg or webm, depending on the exact configuration, either 0 bytes or a few kB is written immediately, and then nothing more until the transcoding is complete (even using -flush_packets 1) — hence I cannot start playing the audio.

  


  By comparison, if I transcode to mp3, the file is written progressively and I can start playing immediately.

  


  Is it possible to transcode to ogg or webm in such a way that the file is written as the transcoding happens, and I can start playing it (almost) immediately ?

  


  Configurations I have tried :

  


  ffmpeg -i orig.m4a -c:a libvorbis -flush_packets 1 vorbis.ogg
ffmpeg -i orig.m4a -c:a libopus -flush_packets 1 opus.ogg
ffmpeg -i orig.m4a -c:a libvorbis -flush_packets 1 vorbis.webm
ffmpeg -i orig.m4a -c:a libopus -flush_packets 1 opus.webm


  


  This is running on Debian (Raspian stretch, specifically) and I would like to do it without adding dependencies from outside of the Debian/Raspian archives, if possible. Sticking with ffmpeg would be my ideal choice but will consider others.

  


• FFmpeg : MD5 hash of M3U8 playlists generated from same input video with different segment durations (after applying video filter) don't match

  30 juillet 2020, par Saurabh P Bhandari

  Here are a few commands I am using to convert and transize a video in MP4 format to a M3U8 playlist.

  


  For a given input video (MP4 format), generate multiple video segments with segment duration 30 seconds.

  


  ffmpeg -loglevel error -i input.mp4 -dn -sn -an -c:v copy -bsf:v h264_mp4toannexb -copyts -start_at_zero -f segment -segment_time 30 30%03d.mp4 -dn -sn -vn -c:a copy audio.aac


  


  Apply a video filter (in this case scaling) on each segment and convert it to a M3U8 format.

  


  ls 30*.mp4 | parallel 'ffmpeg -loglevel error -i {} -vf scale=-2:144 -hls_list_size 0 {}.m3u8'


  


  Store the list of m3u8 files generated in list.txt in this format file 'segment-name.m3u8'

  


  for f in 30*.m3u8; do echo "file '$f'" >> list.txt; done


  


  Using concat demuxer, combine all segment files (which are in M3U8 format) and the audio to get one final m3u8 playlist pointing to segments with duration of 10 seconds.

  


  ffmpeg -loglevel error -f concat -i list.txt -i audio.aac -c copy -hls_list_size 0 -hls_time 10 output_30.m3u8


  


  ---

  


  I can change the segment duration in the first step from 30 seconds to 60 seconds, and compare the MD5 hash of the final M3U8 playlist generated in both the cases using this command :

  


  ffmpeg -loglevel error -i <input m3u8="m3u8" playlist="playlist" /> -f md5 -&#xA;

  


  The MD5 hash of the output files differ, i.e., video streams of output_30.m3u8 and output_60.m3u8 are not the same.

  


  Can anyone elaborate on this ?

  


  (I expected the MD5 hash to be the same)