Little difference between CBR and VBR with H.264 encoder

Mingqian

Hi all,

I am working on DM365 with dvsdk_2_10_01_18 and H.264 encoder ver. 2.00.00.10. Recently, I meet a problem regarding rate control.

I use the following configuration for h.264 encoder ver.2.00.00.10:

	cbr	vbr
rateControlPreset	IVIDEO_USER_DEFINED	IVIDEO_USER_DEFINED
rcAlgo	0	1
InitQ	51	51
rcQMax	51	51
rcQMin	8	8
targetBitrate	2000000	2000000

But I find there be little difference in bitrate variance between CBR and VBR. I tried fixed QP (rcAlgo = 2) with IntraFrameQP and InterFrameQP set to 28, and that shows apparent bitrate variance.

I wonder if this kind of phoenomenon is normal according to codec design.

regards,

Raf

over 14 years ago

0 Ritesh Rajore over 14 years ago

TI__Expert 3065 points

Please refer to below e2e post. Your all doubts will get clear.

http://e2e.ti.com/support/embedded/f/356/p/32788/245623.aspx#245623

You can find more details at below wikiPage

http://processors.wiki.ti.com/index.php/DM36x_Rate_Control_Modes

0 Mingqian over 14 years ago in reply to Ritesh Rajore

Intellectual 635 points

Thanks Ritesh,

I have read that post and wiki before, and i am now confused that WHY rcAlgo = 0 and rcAlgo = 1 has little difference, i.e, bitrate variance with targetBitrate is nearly same for both CBR and VBR.

regards,

Raf

0 Veeranna Hanchinal over 14 years ago in reply to Mingqian

TI__Expert 8465 points

Rafael,

Can you post your encoder parameters?

0 Mingqian over 14 years ago in reply to Veeranna Hanchinal

Intellectual 635 points

Thanks Veeru,

Here is my parameters.

encodingPreset	XDM_HIGH_SPEED
rateControlPreset	IVIDEO_USER_DEFINED
maxFramerate	30000
maxBitrate	8000000
profileIdc	100
levelIdc	31
entropyMode	0
transform8x8FlagIntraFrame	1
transform8x8FlagInterFrame	1
timeScale	60
numUnitsInTicks	1
enableVUIparams	1
seqScalingFlag	0
encQuality	2
enableDDRbuff	1
sliceSize	0
airRate	0
IntraFrameQP	28
InterFrameQP	28
InitQ	51
rcQMax	51
rcQMin	8
rcAlgo	0(CBR)/1(VBR)
maxDelay	2000
lfDisableIdc	0
perceptualRC	1
idrFrameInterval	0
resetHDVICPeveryFrame	0

Raf

0 Ritesh Rajore over 14 years ago in reply to Mingqian

TI__Expert 3065 points

Rafael,

You are observing the expected behavior. CBR and VBR are different rate control algorithms and control bit rate differently. As you might have read in e2e link that the purpose of CBR and VBR is different hence you see bitrate variance.

0 Yashwant Dutt over 14 years ago in reply to Ritesh Rajore

TI__Genius 17215 points

Rafael,

Why are you using DVSDK 2.1? I see you sending various posts on the same.

My first suggestion is that if you are starting afresh on DM36x, please use latest DVSDK 4.x. The same is available on TI site for download. This is important as this DVSDK has the latest of all the componenenst. You may not like to go through the issues which had been fixed by us long back.

http://software-dl.ti.com/dsps/dsps_public_sw/sdo_sb/targetcontent/dvsdk/DVSDK_4_00/latest/index_FDS.html

regards

Yashwant

0 Mingqian over 14 years ago in reply to Yashwant Dutt

Intellectual 635 points

Thanks Yashwant,

I am near finishing DM365 design, and now fixing some bugs. Yes, dvsdk 2_10_01_18 comes with quite a few bugs, but switching dvsdk now seems not reasonable. I will try newer dvsdk in future design.

regards,

Raf