MP4 STSD结构

Question

我有一点怀疑.如ISO-14496-12中所述,moov/mvhd/trak/mdia/minf/stbl/stsd应包含格式特定的盒子,例如ISO-14496-15中描述的avc1盒子或ISO-14496-14中描述的mp42.但它还包含来自QuickTime格式规范的VideoSampleDescription中的字段,例如'version','revision_level','vendor'等.

有谁能解释这个问题？

Answer 1

可以将stsd(样本描述框)视为包含其他框的框.每个样本条目也只是一个普通的框:

 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 )