[FFmpeg-devel] MPEG-4 container header identification

Paul B Mahol onemda at gmail.com
Fri Apr 5 14:58:25 CEST 2013

On 4/5/13, Oliver <ohookins at gmail.com> wrote:
> Hi,
> I've been trying to wrap my head around the MPEG-4 container format and
> while the specifications I've read have been very complete, nothing seems
> to mention the purpose or meaning of the first 4 bytes in the file. From
> what I've seen, these typically are 0x0000001C, 0x00000018 or 0x00000014
> (e.g., listed here: http://www.garykessler.net/library/file_sigs.html).
> This page: http://xhelmboyx.tripod.com/formats/mp4-layout.txt indicates
> that the first 4 bytes are an "offset" but I haven't found any other
> reference to back this up, and my reading of the ffmpeg codebase
> unfortunately didn't shed any light on the subject for me either (mostly
> due to my unfamiliarity with it).
> I was hoping someone might know the purpose of these 4 bytes before the
> ftyp box marker, and if you could point me in the right direction it would
> be much appreciated.

Aren't it size of ftyp box?
> Best Regards,
> Oliver
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