Error using ffmpeg to convert mkv to avi on Windows 7

Question

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?

Answer 1

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"
  

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_{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.}