Doom9's Forum - View Single Post - How to tell if a mp4 file has metadata at the begining or not?

LoRd_MuldeR · 5th September 2013, 18:08

Parsing MP4 files is not that complicated. You always have "boxes" (aka "atoms"), each of which starts with an 8 Byte header (4 Byte size field + 4 Byte name in ASCII).

Boxes may also contain other boxes, but you don't need to care here. Just do the following in a loop: Read the 8 Byte header, then check the name and finally skip over exactly size-8 Bytes to the next box.

Either you will encounter the "moov" box before the "mdat" box - or the other way around. All the meta-data and all the fancy tables are stored within the "moov" box.

5th September 2013, 18:08	#3 \| Link
LoRd_MuldeR Software Developer Join Date: Jun 2005 Location: Last House on Slunk Street Posts: 13,248	Parsing MP4 files is not that complicated. You always have "boxes" (aka "atoms"), each of which starts with an 8 Byte header (4 Byte size field + 4 Byte name in ASCII). Boxes may also contain other boxes, but you don't need to care here. Just do the following in a loop: Read the 8 Byte header, then check the name and finally skip over exactly size-8 Bytes to the next box. Either you will encounter the "moov" box before the "mdat" box - or the other way around. All the meta-data and all the fancy tables are stored within the "moov" box. __________________ Go to https://standforukraine.com/ to find legitimate Ukrainian Charities 🇺🇦✊ Last edited by LoRd_MuldeR; 5th September 2013 at 18:45.