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

[Ian Evans]

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?
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