[mythtv-users] slightly OT: Can dd not be used on mp4?

[Raymond Wagner]

On 9/20/2013 8:43 PM, Ian Evans wrote:
> Trying to create a clip of an mp4 file for debug purposes for another
> thread.Was asked for a 50mb sample since that's easier to send/share
> than the 900mb original.
>
> Created the file with:
>
> dd if=1019_20130918060000.mp4 of=1019_20130918060000_shorttake3.mp4
> bs=1024 count=50000
>
> ffmpeg -i doesn't recognize the new file:
>
> [mov,mp4,m4a,3gp,3g2,mj2 @ 0x339d080] moov atom not found
> 1019_20130918060000_
> shorttake2.mp4: Invalid data found when processing input
>
> is this a command line error or is it not possible to create a debug
> sample from an mp4?

That kind of blind cutting only works on transport streams.