MKV with Mp4v video

[convertinfool]

I was testing a webcam capture in Linux with GUVCViewer. I told the program to save as an MKV using MP4V codec. Little did I know that it was not going to work properly. I can view the saved video in VLC, but I cannot seek (this is a problem because the webcam capture is 2 hours). I cannot extract the video via MKVExtract - I am stuck. At this point I want to convert the video to anything useable. Any advice or suggestion?

[Baldrick]

Try avidemux, open mkv, under audio and video choose copy save as new mkv. If it wont work try ffmpeg, ffmpeg -i video.mkv -acodec copy -vcodec copy new.mkv

If they fails try reconvert the video to for example mpeg4 avc/h264.

[convertinfool]

Thanks Baldrick

I tried both. Avidemux crashed and couldn't even report an error log.

ffmepg returned the message -

"[matroska,webm @ 01AC9CC0] Unknown entry 0x2323E3
[matroska,webm @ 01AC9CC0] Read error at pos. 4297 (0x10c9)
capture813.mkv: Input/output error"

What converter would you suggest?