How to identify frame type in a MP4 file?

[BrianBin]

As title described, In the MP4 file, if we ignore the bitstream data itself, can we get frame type information (I, P, B) from the moov box? and how?
Thanks

[BrianBin]

I think I should reply myself, others please check what I said..
1. We can judge an I frame from 'stss' atom
2. We can identify P and B from the 'ctts' atom, which the value is '0' for B frame, 'non-zero' for an I or P frame

[mediator]

I think it is possible to contruct cases for AVC where your rule is not true any more. E.g. think about B-Frames that always only reference two frames from the past. Such stream can be stored in a valid way to MP4 container without using ctts (ctts for all samples being zero)

[bond]

you can calculate the framerate by mdhd.timescale/stts.sampledelta where there will be only one sampledelta value in stts valid for all frames when the stream is constant framerate

on a variable framerate stream each frame can obviously have its own sampledelta