>>35487227
don't know. In any case
$ dd if=aa.jpg bs=1 skip=54837 of=aa.mp4
2853935+0 records in
2853935+0 records out
2853935 bytes (2.9 MB) copied, 6.15292 s, 464 kB/s
$ file aa*
aa.jpg: JPEG image data, JFIF standard 1.01, comment: "wink jp"
aa.mp4: ISO Media, MPEG v4 system, version 1
I had to use 54837 for some reason. Too tired to think in off-by-1 errors.