[Mp4-tech] Question About H.264/AVC ---- POC - COPY with correctlink

[Gary Sullivan]

+> On Tuesday 20 December 2023 22:00, Ming Yang wrote:
+> > Dear all:
+> >
+> > I have some questions about H.264/AVC JM10.1:
+> >
+> > (1) What does POC mean in the decoder output?
POC increases with output order, but gaps in POC values are allowed.  They don't mean anything.
Also POC is used for the scaling of certain parameters in the decoding process, such as motion vector values for "temporal direct" prediction and weight values for "implicit weighted prediction".
+> >
+> > (2) What does POC Gap mean?
Nothing.
+> >
+> > (3) What does IPP /IbP/IpP mean?
That's informal terminology.  It is not found in the standard.  I'm guessing that each lower-case letter refers to a non-reference picture of the type indicated by the letter (although the concept of a B or P picture type is also informal terminology also not found in the standard).
+> >
+> > (4) Howcome the output frame #s are always:
+> >       0000
+> >       0002
+> >       0004
+> >       0006
+> >       .........
NOTE: I suspect that those are not actually frame #s (i.e., they are not frame_num values), but rather that they are POC values.
+> > they are not consecutive numbers no matter how I set IntraPeriod,
+> > FrameSkip, and NumberBFrames. Even if the original video 
+> sequence is
+> > encoded as all I-frames, the output is still like this.
That's just the way that particular encoder operates.  Other encoders may act differently.  Numbering gaps are allowed.  This particular behavior was convenient when developing this encoder, but it's probably not worth studying why, as it has very little to do with the standard itself.
Best Regards,
Gary Sullivan
+> >
+> > Can anybody explain this to me? Thank you very much.
+> >
+> > Ming
+> 
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