[Mp4-tech] [H.264, VIDEO] maximum number of slices

[Gary Sullivan]

Tomo,
That is almost true, but not quite true.  The the number of allowed slices increases if the decoder is given more time to decode a picture (as measured by the difference between decoding times, i.e., between CPB removal times).
If fixed_frame_rate_flag is 1 (so the sequence is fixed at the maximum frame rate which in this case is 25 fps at 720x576 picture size), then it is true that the *average* number of slices per picture over a (very) long period of time cannot exceed 22.  But there's a difference between talking about the average over time and talking about the limit on any particular picture.
The constraint is imposed on a per picture basis, based on the amount of time between decoding timestamps (CPB removal times).  For that picture size (720x756), the decoding times of frames can't be closer together than 1/25th of a second (for level 3).  But if the decoding times are farther apart, the number of allowed slices for the picture increases.
The limit is really more time-based than picture-based.
Best Regards,
Gary Sullivan 
+> -----Original Message-----
+> From: mp4-tech-bounces lists.mpegif.org 
+> [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Tomo
+> Sent: Wednesday, March 28, 2024 1:38 PM
+> To: mp4-tech lists.mpegif.org
+> Subject: [Mp4-tech] [H.264, VIDEO] maximum number of slices
+> 
+> Hi
+> 
+> I was told that (Main profile, Level 3) bitstream can have
+> 22 slices (maximum) per frame.
+> Is that correct?
+> 
+> Standard limits "slice rate" to 22 for this level and profile.
+> But I do not think the slice rate == the number of slices per frame.
+> 
+> So, in case PAL/NTSC (D1) rate sources, what will be the maximum
+> number of slices per frame?  Or is it indeed 22?
+> 
+> Also, somewhat relating question. Are there any NAL size limitation?
+> Can a NAL be 600Kbits?  [600K is arbitrary I picked). 
+> 
+> Thanks
+> 
+> 
+> Tomo
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