[Mp4-tech] [H.264] FMO: Standard and JM

[Gary Sullivan]

Reply interspersed below.
Best Regards,
Gary Sullivan
+> -----Original Message-----
+> From: mp4-tech-bounces lists.mpegif.org 
+> [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Luca
+> Sent: Wednesday, July 18, 2023 5:48 AM
+> To: mp4-tech lists.mpegif.org
+> Subject: [Mp4-tech] [H.264] FMO: Standard and JM
+> 
+> Dear Experts,
+> 
+> I have a couple of questions concerning the FMO capabilities in the 
+> standard and its implementation in the JM software.
+> 
+> 1) Does the standard allow the definition of a different QP for each 
+> considered FMO-region?
Yes, and it furthermore allows changing the QP for each macroblock within any region if that is desired too.
+> 2) Does the standard allow a "smart" encoding of the mapping 
+> of MB index 
+> to FMO-Region using "explicit mode" (in the PPS)? The software just 
+> encode for each MB the corresponding FMO-Region.
There are perhaps a half-dozen special patterns that are supported with distinct efficient signaling mechanisms in the syntax.  For cases where the actual pattern needs to deviate from the pre-defined special patterns, there is the obvious mode that you mentioned: just sending the slice group identifier for each entry in the map.
It may also be worth pointing out that the number of bits used to represent the map may not be especially critical, since this is sequence parameter set information.  Such very-high-level syntax is likely to be a vanishingly-small percentage of the total video bit rate.
+> 
+> Thank you for your attention,
+> 
+> Greetings,
+> Luca.
+> 
+> 
+> 
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