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Old 11th August 2009, 16:01   #1  |  Link
iw2z
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Quicktime files metadata

hi
i'm not sure of this is the right place for this question, but i'll ask anyway...
i've been working on an application that will give me some general info about a quicktime video file (Dimensions, Frame Rate, Compressor Name, Audio channels...)

so i read the "Quicktime File Format Specification" document from apple.com, and i did get to read most of the data i need from the corresponding atoms (atoms are the building units of a quicktime file), but i came across some files that didn't have these atoms at all (since most of these atoms are optional)

examples include
- 'stsd' atoms hold the compressor name, but it's optional
- 'stts' atoms hold data vital to the frame rate calculation, also optional
- 'stss' atoms hold data regarding key frames, also optional

and even though one of the atoms i need isn't even optional, i still couldn't find it ('tkhd' for the video dimensions)

but when i open these files (which missing atoms) they work well, and when i open them in VLC player, i can see the data i need in the 'media information' provided by the player

so my question is: how can i get the data i need even when the atoms aren't available? (it must be doable, VLC proves that!)
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Old 11th August 2009, 16:10   #2  |  Link
Ritsuka
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QTVR or sprite tracks are strange beast. You need to handle them separately. (if that is what your file contains). What does QuickTime says?

Last edited by Ritsuka; 11th August 2009 at 16:12.
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Old 16th August 2009, 07:03   #3  |  Link
iw2z
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i did a little extra goofing around, the file i have has cmov (compressed movie) atom which contains a dcom and a cmvd atoms, but i'm clueless after that, any suggestions?
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Old 17th August 2009, 15:53   #4  |  Link
iw2z
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problem solved!

ok i finally got this problem solved, so here's the solution in case someone else needs it:

having a 'cmov' (compressed movie) atom means the movie resource has been compressed (ok that's really obvious!)
now this 'cmov' atom contains 2 other atoms:
1-'dcom' (data compression) atom
2-'cmvd' (compressed movie data) atom

dcom only contains 4 bytes for the size, 4 bytes for the atom type, and 4 bytes for the compression algorithm
(all files i came across had 'zlib' as the compression algo)

cmvd contains 4 bytes for the size, 4 bytes for the atom type, 4 bytes for the size of the uncompressed content, and the compressed content itself

so java standard library already contains a decompressor for zlib and voila, the uncompressed data contains the missing atoms
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