when I muxyng .mkv file and .ac3 file without converting I had next errors:

  • [ac3]Estimating duration from bitrate, this may be inaccurate
  • [matroska]Starting new cluster due to timestampe
  • muxing overhead: 0.078666%

ac3 error output appears before .ac3 file information enter image description here

mkv and muxing overhead in end of console output appears enter image description here

Script that i use:

ffmpeg -i input1.mkv -i input2.ac3 -map 0:v -map 1:a -map 0:a -map 0:s -c:v copy
-c:a:1 copy -c:s copy -metadata:s:a:0 language={lang} -metadata:s:a:0 title="title1"
-metadata:s:a:1 title="title2" output.mkv

I try to copy .mkv file and .ac3 separately and .mkv copying only with muxing overhead and .ac3 cppying with ac3 error(without muxing overhead). Could you explain what the reason of this problem, and help me with it? Also after muxing in the end of output video file absent small part of audio stream from second file! How To manage with this issue?


  • There aren't any errors, only info messages. – Gyan Aug 19 '17 at 13:53
  • Yes, but there is no small part of audio stream in the end of output film – ZakZand Aug 19 '17 at 14:22
  • Run ffmpeg -i input2.ac3 -c copy input2.mp4 and then try your command with this new file. – Gyan Aug 19 '17 at 20:57
  • Mulvya, no, I do it even with ac3 encoding, but in the end, when I copy this streams in 1 output files I have 3 minutes empty audio stream in the end of film. As I understand this issue appears because size of concrete video frame not comparable with audio stream frame... Do you have any idea what argument should I set in script to solve this issue? May be set bitrate or buffer size? – ZakZand Aug 20 '17 at 21:55
  • Share the full log of the command. – Gyan Aug 21 '17 at 5:01

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