How to tell if a mp4 file has metadata at the begining or not?

karasu · 5th September 2013, 08:25

As I'm working with files for the web, I sometimes need to know if the mp4 files I recieve have their metadata at the begining. Mediainfo does not seems to provide such informations.
What tool can I use to check that? (Linux or OSX)

Thank you.

sneaker_ger · 5th September 2013, 08:50

With the l-smash boxdumper you could look whether the Media Data Box is at the end 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.

ganymede · 5th September 2013, 19:02

Quote:

Originally Posted by karasu

What tool can I use to check that? (Linux or OSX)

MP4Box from the gpac package can do that.

Code:

MP4Box -info -v file.mp4

If you only need to check that moov is before mdat, -v (verbose) is not even necessary : MP4Box -info will display "File suitable for progressive download (moov before mdat)".

karasu · 7th September 2013, 15:46

Thank you, MP4Box is exactly the tool I need.

5th September 2013, 08:25	#1 \| Link
karasu Registered User Join Date: Jun 2006 Posts: 111	How to tell if a mp4 file has metadata at the begining or not? As I'm working with files for the web, I sometimes need to know if the mp4 files I recieve have their metadata at the begining. Mediainfo does not seems to provide such informations. What tool can I use to check that? (Linux or OSX) Thank you.

5th September 2013, 18:08	#3 \| Link
LoRd_MuldeR Software Developer Join Date: Jun 2005 Location: Last House on Slunk Street Posts: 13,275	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.

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5th September 2013, 08:50	#2 \| Link
sneaker_ger Registered User Join Date: Dec 2002 Posts: 5,565	With the l-smash boxdumper you could look whether the Media Data Box is at the end or not.

7th September 2013, 15:46	#5 \| Link
karasu Registered User Join Date: Jun 2006 Posts: 111	Thank you, MP4Box is exactly the tool I need.