I create the movie on iphone 4 with ALAssetsWriter 'connected' to a
AVCaptureSession.
as i understand it a valid frame should have the following appearance:
00 00 00 01 XX data -------------
where XX is say whether it is a I-,P- or B-frame. or more specifically
type(XX) = 0x0F && XX says if it is I(type(XX) = 5?),P(type(XX) = 7?)
or B(type(XX) = 8?) frame. I'm not sure about these number, i've been
looking for it but not found good sources. so that's question number
one, what number should the NALU be for the different frame types?
anyway, when i look at the mov file in hex editor, the mdat atom
contain frames that looks like this:
4B = size, 1B = XX and then data. (at least this is what i think i get)
i split the the mdat atom and store the frames in files. the files are
always size long when i look at them in a hex editor(otherwise as well
of course). and XX is always 65(ie. type(XX) = 5) in the first and
then 61(ie. type(XX) = 1) for a couple of frames and then back to
being 65 for one frame and so on.
i guess that these are frames like: I P P P P P P I P P P P P P P I P
P P P P P P .... however then my assumption about the type numbers for
the different frame types are false, which is highly likely. (any
suggestion on reading about this? except the ISO/IEC 14496-10, i don't
really understand it).
I've tried to remove the size and append 00 00 00 01 before the XX
byte and the data but without success. any tips on how i could modify
the frames to be valid H264 encoded frames?
Also the avcC atom, i understand that it contains the sps and pps but
i don't know what these say, tried googling to find the structure of
these, but without success, please point me in the right direction
here. I don't know if I really need these since i only want the h264
encoded frames one by one.
Thanks in advance
Robin Rye
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