[FFmpeg-user] Empty File: Trouble Making A Clip From An MP4

[Steve]

Hi,

I tried making a clip from an MP4 with the command below:

ffmpeg -ss 00:00:15 -t 00:00:10 -i input.mp4 -c:v copy -c:a copy output.mp4

I'm running Kubuntu 11.10

The resulting clip had a file size, but everything I tried to play it
in gave me an error message of one sort or another, claiming it was
unplayable.

Any help will be greatly appreciated

Thanks

Steve