How to convert MKV to AVI AC3

[MLG]

I try to do this and it only give me 3:48sec but when i try it from AVI to AVI it work fine , i am trying to encode the video from mkv file and leave or encode the audio to AC3 and is not working for me do anyone know whast going on thank you and advance

[MLG]

i try to encode the MKV again but a different one and still give me 3:48 sec i will try using on another setting if it dont work going back to what i had b4 been trying this for 2 days and nothing.

[Case]

It is possible that there is an error or glitch in the MKV, making it hard for ffmpegX to process. Perhaps there is something at 0:03:48 that makes the decoder think that it reached the end of the file.

Try a mencoder preset.
Try an ffmpeg preset with QuickTime decoding. (Make sure to install Perian.)
Try an ffmpeg preset without QuickTime decoding.

[MLG]

It is possible that there is an error or glitch in the MKV, making it hard for ffmpegX to process. Perhaps there is something at 0:03:48 that makes the decoder think that it reached the end of the file.

Try a mencoder preset.
Try an ffmpeg preset with QuickTime decoding. (Make sure to install Perian.)
Try an ffmpeg preset without QuickTime decoding.

it dont work been trying to get ac3 on movie fr 3 days with this and no luck lol and when i do get it is 2ch and not 6 like it suppose to be 5.1 , and also when i get it a-c3 with 2 channels the sound is real low cant even hear it at al when i put it on vlc i can hear it a lil bit home some one can help me with this buy trying a mkv file them self and try to convert it to and avi xvid ac3 5.1 sound and get back to me with the setting or with what is really wrong thank you for the help.