On 6/20/14 5:42 AM, Miladin Sajic wrote:
Hi,
I am trying to implement decoding of H264 NAL units that are received
from the camera (using live555 rtsp streaming). Everything works fine
if received NAL unit is IDR (see part of the code in PS) but it does
not work for SLICE NAL unit (nal_unit_type == 1). To decode image this
NAL unit is not enough on its own and reference needs to be made to
all the units since last IDR unit (key frame with nal_unit_type == 5).
I do not know how to implement this.
How to combine last IDR unit with the following SLICE NAL units to
produce H264 frame before sending it to the decoder?
Can you give me any advice or point me to the right direction?Any help
is greatly appreciated.
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Sorry Ross for continuing the OT discussion, but just real quick. The
answer to your decoding question lies in the question itself, you said
that non idr slices can reference any prior nal up to the last idr. So
in order to decode, you need to pass all prior nals up to the last idr.
How exactly you do this depends on the decoder library you're using, ie
ffmpeg requires that you provide the full bitstream each call to the
decoder, hence (sc = startcode)
sps sc pps sc idr frame 1
sps sc pps sc idr sc slice frame 2
sps sc pps sc idr sc slice sc slice frame 3
and so on.
I can imagine a decoding library frontend that keeps track of the
unchanging parts of the bitstream for you, and I wonder why it doesn't
already exist, ie
you pass nals in receive order to the decoder library and then ask the
library to give you a frame. Eventually, once it has enough info, you
get a frame back each call, while only having to briefly store the
latest nal on behalf of the library.
I know this is OT, but if I'm mistaken someone please speak up.
--
Joshua Kordani
LSA Autonomy
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