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2 days ago I had troubles with video conversion, today that's audio. Here is the problem, the converter I found (see this question) detects all my sources audio channels as different channels (like if they were dvd languages) :

enter image description here

The first chanenl is the left speaker, and the second one is the right speaker, all others are middle's one. When I convert my video, the output is stereo but I loose one speaker. Here is an image to understand :

enter image description here

I gave a different color to each channels of my source : as you can see, after output, only the selected input is used for both speakers.

I suspect this software not to handle 5.1 channels as source. Because this is the only soft I found that supports my image resolution, I need to keep it for video conversion. But I first need to convert dolby to sereo using another software.

Do you know a way to convert dolby to stereo, without altering video ?

edit: ffmpeg -i <video> command gives this output.

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Do you want to discard everything except left and right, or do you want to downmix (combine specific channels into left and/or right)? Which channels should go where? –  LordNeckbeard Dec 16 '12 at 17:45
    
I want to discard everything except left and right. I keep original files for HD purposes but there, that's for sharing. Thanks –  Ninsuo Dec 16 '12 at 20:37
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You can do this with ffmpeg (OS X static builds). It can copy the video, so no need to re-encode, and select specific audio channels for the output. If you show the ffmpeg console output of ffmpeg -i input I can give an example command. –  LordNeckbeard Dec 20 '12 at 3:41
    
Whoa, a command-line, I dreamt ot that! The output of this command is pastebined here. There is yellow warnings about unimplemented channels, but all info are there anyway. –  Ninsuo Dec 20 '12 at 9:11
    
Shoudn't the audio 5.1 mix be remixed for stereo?? –  Chris James Champeau Dec 20 '12 at 22:33
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1 Answer 1

up vote 5 down vote accepted

You can use the amerge and pan filters in ffmpeg to combine two mono streams into one stereo output:

ffmpeg -i input -filter_complex "[0:3] [0:4] amerge,pan=stereo:c0=c0:c1=c1" -c:v copy -c:a pcm_s16le output

or using -ac instead of pan:

ffmpeg -i input -filter_complex "[0:3] [0:4] amerge" -c:v copy -c:a pcm_s16le -ac 2 output

[0:3] and [0:4] refer to your desired audio streams as shown in your ffmpeg output. I just chose these as examples. There are other audio filters and options too, so there are probably several other ways to do this.

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You are the man of my day. –  Ninsuo Dec 20 '12 at 20:24
    
@Ninsuo Glad it worked for you. I forgot to mention that if you want to switch the channel locations then you can simply switch the positions of [0:3] and [0:4] as in "[0:4] [0:3] amerge". –  LordNeckbeard Dec 20 '12 at 20:53
    
Thanks I understood the command-line. For me that's [0:1] for left and [0:2] for right. Works like a charm. –  Ninsuo Dec 20 '12 at 21:11
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