[MPlayer-dev-eng] Distinction between I and P frames

[Stefan Gehrer]

Marek ... wrote:

>I-frame should be in evry 4. frame, 
>
Where is this information from? A QuickTime setting?

>
>P.S.: Payload of RTP packet of h.263 video (first 10 bytes):
>I-frame:
>04 00 80 02 08 01 26 e8 e8 e8
>
>P-frames (but i think that these are I-frames - because of reason above):
>04 00 81 26 0a 07 03 38 78 a8
>04 00 80 c2 0a 01 00 e1 08 0f
>
>P-frames:
>04 00 81 02 0a 03 00 66 f0 f6
>04 00 81 16 0a 03 00 64 7d ff
>
 From a quick check I would have the same interpretation of the headers 
as you.
picture_coding_type indicates I-frame only in the first, P-frame in the 
others.
Having intra macroblocks is allowed in P-frames too, so maybe the 
refresh you see
is caused by P-frames full of intra macroblocks or at least stripes of intra
macroblocks, which is a common method of reducing error drift too.
If it is done this way, there is no way to know "how much intra" one 
frame is
just by parsing the headers, you can only know it after decoding the 
complete frame.

Regards
Stefan

P.S.: this seems a little off-topic for this list.