Re: Captured Video Not Producing Sound on Some Systems

[Rob Owens <rowens@ptd.net>]

On Sat, Oct 23, 2010 at 07:24:15PM -0700, Scarletdown wrote:
> Just out of curiosity, I brought up in Audacity the mp3 file from one
> of the videos and saw that the left channel was blank, while all the
> music was in the right channel (which I guess could be considered the
> secondary channel in a stereo track.)  Apparently, some sound hardware
> can't "hear" a file like this.  The channel with sound has to be the
> left channel in a situation of this sort.
> 
That was a hunch I had, and I corrected it in the sample video I sent
you.  Here's what I did.

1)  Get the audio track from the video:

ffmpeg -i yourvideo.flv -vn sound.wav

2)  Get the video track from the video:

ffmpeg -i yourvideo.flv -vcodec copy -an video.flv

3)  Open the audio track in Audacity.  On the left of the screen, click
the drop-down menu next to the audio track name.  Choose "split stereo
track".  Now you can delete the bad audio channel, then copy and paste
the good one over.  Then export as something lossless (flac or wav --
I'll use sound-fixed.flac in my example).

Note that you could instead do "Stereo to Mono" under the Tracks menu,
but that combines the good and bad channel, resulting in half the volume
of the original.

4)  Combine the video with the corrected audio:

ffmpeg -i video.flv -i sound-fixed.flac -vcodec copy yourfixedvideo.flv


Explanation of some ffmpeg switches:

-vn = no video
-an = no audio
-vcodec copy = do not recompress the video

I'm not an expert in this stuff, so there might be some mistakes.  I'm
still learning...

-Rob