Welcome to Doom9's Forum, THE in-place to be for everyone interested in DVD conversion.

Before you start posting please read the forum rules. By posting to this forum you agree to abide by the rules.


Go Back   Doom9's Forum > Video Encoding > MPEG-4 AVC / H.264

Thread Tools Search this Thread Display Modes
Prev Previous Post   Next Post Next
Old 10th December 2013, 04:23   #1  |  Link
Registered User
Join Date: Sep 2013
Posts: 38
VBV-CBR and ABR in X264

In x264 VBV-CBR RC mode is based on ABR and vbv-maxrate and vbv-bufsize are set. On the basis of frame QP decided by ABR, the MB row QP is decided by VBV-CBR for each row. I test these two modes and the command lines are listed:
ABR: -o BasketballDrill_832x480_50_20131210102507.264 BasketballDrill_832x480_50.yuv 832x480 --fps 50 --frames 300 --bitrate 1120 --profile baseline --threads -1 -I 50 -v --psnr
VBV-CBR: -o BasketballDrill_832x480_50_20131210102507_mb.264 BasketballDrill_832x480_50.yuv 832x480 --fps 50 --frames 300 --bitrate 1120 --vbv-maxrate 1120 --vbv-bufsize 1680 --profile baseline --threads 1 -I 50 -v --psnr

The final results are:
ABR: Y-PSNR 31.530dB, bitrate 1146.93kbps
VBV-CBR: Y-PSNR 31.728dB, bitrate 1230.25kbps
Compared to ABR, VBV-CBR achieved 4.9% bitrate promotion and 0.198dB PSNR promotion. But the PSNR promotion is lower than bitrate (1% bitrate=0.05dB).

Having talked so much, I just want to ask what is the advantage of VBV-CBR compared ABR? If ABR can get the reasonable results, why the VBV-cBR is needed?
In my opinion, VBV-CBR maybe can promote the subjective quality owing to deciding the QP for each MB row. But the bitrate also rises. Also I have compared some frames of the two modes, they are almost the same.
Maybe there are some situations that are fit for VBV-CBR and I don't know. So guys, give me, the new to x264, some professional explanation.

Last edited by xkfz007; 10th December 2013 at 07:30.
xkfz007 is offline   Reply With Quote

abr, vbv-cbr, x264

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT +1. The time now is 19:23.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2022, vBulletin Solutions Inc.