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I am using ffmpeg on a Windows 7 machine. I am trying to convert mkv files to either mp4 or avi. Here is the command I used:

ffmpeg -i "C:\Path\To\Input.mkv" "C:\Path\To\Output.avi"

Here is the error I get:

[libmp4lame @ 00000000004624800] Invalid number of channels 6, must be <=2

and after a few lines about what my output file should have been I get this error:

Error while opening encoder for output stream #0:1 - maybe incorrect parameters such as bit_rate, rate, width or height

I didn't specify any of those parameters because I wanted ffmpeg to copy them over from the source file. What am I doing wrong and how do I fix it?

share|improve this question
Please edit your question and post the full output of your FFmpeg command. – slhck Dec 25 '11 at 11:27
I did this in windows from the dos prompt which doesn't allow you to copy output, and there are waaaaaaaaaaay too many lines for me to copy the full output here. – aamiri Dec 27 '11 at 15:40
Of course it's possible:… – slhck Dec 27 '11 at 15:51
up vote 6 down vote accepted

Without you posting the full output I can only assume things here, but it's most likely the following issue:

Your MKV file contains 6-channel surround sound. When converting it to AVI, FFmpeg assumes some default codecs for both video and audio. I guess in your case this will be MPEG-4 video and MP3 or MP4 audio.

Anyway, there's no way to get 6-channel sound in LAME MP3, therefore you can try either of the following:

  • This will try and copy the AC3 (or whatever it is) stream.

    ffmpeg -i "C:\Path\To\Input.mkv" -acodec copy "C:\Path\To\Output.avi"
  • This will try and downsample to two audio channels:

    ffmpeg -i "C:\Path\To\Input.mkv" -acodec libmp3lame -ac 2 "C:\Path\To\Output.avi"

I'm actually quite confident that the error message should say libmp3lame and not libmp4name. Please copy/paste output instead of just typing it, and always supply full output.

share|improve this answer
I don't know how to (or if it's even possible) to copy text from the dos prompt. – aamiri Dec 27 '11 at 15:41

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