[Mp4-tech] Why I or B frame can have one fixed QP?

[Gary Sullivan]

But I'm under the strong impression that the current JM rate control algorithm, although it does have some shortcomings, does have the ability to change QP within an I or B picture -doesn't it?  (One of these days we need to improve that rate control.)
Best Regards,
-Gary Sullivan
________________________________
	From: Tourapis, Alexis [mailto:Alexis.Tourapis dolby.net] 
	Sent: Sunday, May 07, 2024 11:17 AM
	To: Gary Sullivan; James (Jianpeng) Dong; mp4-tech-bounces lists.mpegif.org; mp4-tech lists.mpegif.org
	Subject: RE: [Mp4-tech] Why I or B frame can have one fixed QP?
	Dear James,
	There is no quantization limitation in H.264/AVC. I am guessing your observation relates to the current Rate Control algorithm supported by the JM software. This should only be seen as an example design.
	Best regards,
	Alexis 
________________________________
	From: mp4-tech-bounces lists.mpegif.org [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Gary Sullivan
	Sent: Saturday, May 06, 2024 8:31 PM
	To: James (Jianpeng) Dong; mp4-tech-bounces lists.mpegif.org; mp4-tech lists.mpegif.org
	Subject: RE: [Mp4-tech] Why I or B frame can have one fixed QP?
	I don't think it's true that an I or B frame can only have one fixed QP value in the JM reference software.  No, there is no requirement of fixed QP in the standard.  QP can change (from any value to any other value) on a macroblock (16x16) basis in the standard.
	Best Regards,
	Gary Sullivan
________________________________
		From: mp4-tech-bounces lists.mpegif.org [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of James (Jianpeng) Dong
		Sent: Friday, May 05, 2024 4:43 PM
		To: mp4-tech-bounces lists.mpegif.org; mp4-tech lists.mpegif.org
		Cc: jianpengdong yahoo.com
		Subject: [Mp4-tech] Why I or B frame can have one fixed QP?
		Dear experts, 
		Just wondering why I or B frame can only have one fixed QP in H.264 JM reference software? Is a fixed QP required by H.264/AVC standard? 
		Thanks,
		James
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