[FFmpeg-trac] #4214(undetermined:new): Conversion to mp3 changes audio duration

[FFmpeg]

#4214: Conversion to mp3 changes audio duration
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             Reporter:  smosek       |                    Owner:
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:
              Version:  unspecified  |  undetermined
             Keywords:               |               Resolution:
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
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Comment (by smosek):

 I don't see a duration value in the XING header.
 I did find that when writing the XING header, the XING frame has a bitrate
 of 24kbps, while the rest of the frames have a bitrate of 8 kbps. This
 goes well with the fact that opening the audio in an HTML5 player in IE
 shows a length of 20 seconds for the audio (instead of 1 minute).
 If I manually modify this bitrate to 8kbps, the audio duration is correct
 in the HTML5 player.
 I believe FFMPEG writes the XING frame as though the audio was stereo even
 if it is mono audio, which is the cause of the problem. This also explains
 why the problem is not seen with stereo calls.

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Ticket URL: <https://trac.ffmpeg.org/ticket/4214#comment:10>
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