MP4 STSD structure

问题:

I doubt in one thing. As described in ISO-14496-12 moov/mvhd/trak/mdia/minf/stbl/stsd should contain format specific box e.g. avc1 box described in ISO-14496-15 or mp42 described in ISO-14496-14. But it also contains fields in VideoSampleDescription from QuickTime Format specification such as 'version', 'revision_level','vendor', etc.

Could anyone explain this issue?

回答1:

The stsd (Sample Description Box) can be treated like a box that contains other boxes. Each Sample Entry is also just a normal box:

 4 bytes - length in total
 4 bytes - 4 char code of sample description table (stsd)
 4 bytes - version & flags
 4 bytes - number of sample entries (num_sample_entries)
 [
    4 bytes - length of sample entry (len_sample_entry)
    4 bytes - 4 char code of sample entry
    ('len_sample_entry' - 8) bytes of data
 ] (repeated 'num_sample_entries' times)
(4 bytes - optional 0x00000000 as end of box marker )