Parsing H264 in mdat MP4

Question

I have a file that only contains the mdat atom in a MP4 container. The data in the mdat contains AVC data. I know the encoding parameters for the data. The format does not appear to be in the Annex B byte stream format. I am wondering how I would go about parsing this. I have tried searching for the slice header, but have not had much luck.

Is it possible to parse the slices without the NAL's?

Answer 1

AVC NAL units are in the following format in MDAT section: [4 bytes] = NAL length, network order; [NAL bytes] Shortly, start codes are simply replaced by lengths.

Answer 2

Be careful! The NAL Length is not required to be 4! The AvcConfigurationBox ('moov/trak/mdia/minf/stbl/stsd/avc1/avcC') contains a field 'lengthSizeMinusOne' specifying the length. But the default is 4.

Answer 3

I found what michael was talking about defined in section 5.2.3 of ISO 14496-15.

Sebastian's answer refers to section 5.2.4.1.1 and 5.3.4.1.2.

You will not be able to parse the slices in the 'mdat' box without copies of the SPS and PPS from the 'avcC' box (defined in section 5.2.4.1.1)