Pointer to I-frame extra data in H.264?

[Javiku]

Hi,

I am working on a project where I need to feed some application functions
with the output of an H.264 encoder (v4l2h264enc). Those functions expect a
pointer to the encoded data and a second pointer to the "extra data" from
the I-Frames. This extra data is defined in the application documentation as
follows:

"The extra ancillary data required to configure an H.264 codec must
correctly be provided. This must exist for all I-
frames. The structure of this data should contain concatenated NAL units in
Annex B format, along with their start
codes. For H.264, they are the SPS and PPS NAL units."

So far I managed to create an appsink, link it to a tee object and use a
callback to extract a buffer every time a new sample is generated. Then I
mapped that buffer to get the pointer to the data (map.data) and de data
size (map.size) as well. But I could not get any further because the
GstMapInfo structure does not provide any specific field for I-frames extra
data and I could not find it in the GstSample or GstBuffer structures
either. By the way, I am checking if the GST_BUFFER_FLAG_DELTA_UNIT flag is
not set to find the I-frames, which seems to work fine because the buffers
are way bigger when that happens (once every 30 frames at 30 fps).

I was wondering if there is a specific structure member where I could find
this extra data or if I should look for it somewhere else... maybe packed
within the data block? I had a look at the first bytes of my I-frames and
they start with 0x00 0x00 0x00 0x01 0x07 0x42 0x40 0x28... as other non
I-frames do (maybe P-frames). Could that data be the extra data (SPS and PPS
NAL units) anyways? The GST_BUFFER_FLAG_HEADER flag is never set though.

Thanks a lot for your help, best regards,
Javiku



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