[Mp4-tech] [H.264 Video] Question about decoded frames ordering for output

[Alejandro Moya]

Hi again, everyone!
I have a couple of doubts about the use of POC in decoded frames.
First of all, when finished decoding an IDR frame, this one can be
outputted directly to the display or maybe there could be any later
frame in decoding order that should be send to the display before this
IDR frame? I mean, let's say this is the decoding order:
POCs ->    ... 24 -  21 -  20 - 19 - 25 -  0(IDR) - 2 - 26(Delayed
frame) - 4 - 3....
Could be this situation posible in any H.264 bitstream at any level or profile?
And the second question is about real-time applications of H.264.
Let's say the maximum allowed delay is 1 frame for some real-time
scenario... Is it a good idea to use POC Type 0 or 1 in this
situation? I think that the decoder should wait to fill all its DPB
before sending to the output any decoded frame, so this delay makes
POC Type 0 and 1 not suitable for real-time. Or maybe I am wrong? I
got to this conclusion analyzing sequences like this one:
POCs (POC Type = 0) ->    .... 0(IDR) - 2 - 4 - 6 - 3 - 1 - 5.....
The decoder can't display any frame till the one with POC 1 is
decoded, whereas in the following situation, the sequence is properly
ordered in decoding order so it could be displayed without any delay:
POCs (POC Type = 0)->     ..... 0(IDR) - 2 - 4 - 6 - 8 - 10 - 12.....
I suppose all sequences have only I and P slices.
Thank you all in advance!!