[Mp4-tech][video][H.263] Relative output order of B-pictures and B-parts of PB-pictures?

[J. Miles]

Hi everyone.
I am working with H.263 decoding, and I hope someone can help me clarifying
the relative output order of B-pictures and B-parts of PB-pictures (or
Improved PB-pictures) in H.263. I do not find the standard clear on these
subjects. From the standard it is clear that the B-part of a PB-picture is
always output before the P-part, which is also intuitive to the usual
definition of B-pictures from e.g. MPEG-2 (=H.262) for enabling
bi-predicition. The same seems to go for B-pictures when just having these
in the stream (i.e. no PB-pictures). For example, a simple stream with just
two PB-pictures between each P-picture will be output as follows:
 Coded input order:    I0 | P1 | PB2 | PB3 | P4 | PB5 | . . .
 Decoded output order: I0 | P1 | B2* | P2 | B3* | P3 | P4 | B5* | P5 |. . .
How would the relative output order look for a stream containing both 'true'
B-pictures and B-parts of PB-pictures? Would the B-parts come out first
(similar to a stream without B-pictures as in the example above), or are the
B-pictures output first? In the example below there are two B-pictures
between each PB-picture, and the first output ordering in [1] outputs the
B-parts first (marked with *), whereas in [2] the B-pictures are output
first.
 Coded input order:        I0 | P1 | PB2 | B3 | B4 | PB5 | B6 | B7 | . . .
 Decoded output order [1]: I0 | P0 | B2* | B3 | B4 | P2| B5* | B6 | B7 | P5
| . . .

 Decoded output order [2]: I0 | P0 | B3 | B4 | B2* | P2| B6 | B7 | B5* | P5
| . . .

What is the correct handling of output ordering?
I am also wondering if anyone know of any test streams that contain both
B-pictures and PB-pictures that I can use for testing/checking?
Any help and comments would be appreciated. Thanks.
Jay
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