XMedia Recode: VBV Control Settings

[yomle]

Hello everyone, I'm trying to convert some videos from 1920x1080 to 720x480 using XMedia Recode.
I've noticed that with XMedia Recode, using a custom MP4/MKV profile with the stream control set to 'constant quality,' 'quality: 20,' and 'level: 3.1,' the program sets 'VBV buffer size' to 14000 and 'VBV max bitrate' to 2400. However, when using Handbrake with the 'fast480p' profile, the program sets 'VBV buffer size' to 14000 and 'VBV max bitrate' to 14000. I'm wondering if I should stick with the values set by XMedia Recode or if I should adjust the parameters to match those of Handbrake. What would be the best settings to achieve high-quality conversion from 1920x1080 to 720x480? Thank you in advance for your help!

[davexnet]

I've never messed with these settings; I assumed that x264 just picked them (unless overridden) based on defaults
associated with the prolfile/level and rate control settings.
See this for more info:
https://slhck.info/video/2017/03/01/rate-control.html

[yomle]

I've never messed with these settings; I assumed that x264 just picked them (unless overridden) based on defaults
associated with the prolfile/level and rate control settings.
See this for more info:
https://slhck.info/video/2017/03/01/rate-control.html

If I set the VBV maximum bitrate to 0, which is the Default, is it okay?

[Selur]

x264 does not set vbv restrictions by itself (even if you set profile&level settings!).
About level 3.1 using 14 000 is the max allowed settings for this level.
Using 2400 will restrict the choices the rate control of the encoder can make, and thus might force the encoder to use higher quantization values than necessary to be level compliant.

XMedia Recode probably uses 2400, since:
a. they assume that most SD content encoded doesn't use high bit rates anyway (if your encode is ~800kbit/s setting a max of 2400 usually is fine
b. the result will be easier to decode (since bit rate fluctuation is more restricted) for really old hardware

=> Personally, I would stick with the max allowed value unless I got specific hardware which does not even support the full 3.1 level restrictions.

afaik. setting one vbv value to 0 will disable all vbv restrictions.

Cu Selur

[yomle]

x264 does not set vbv restrictions by itself (even if you set profile&level settings!).
About level 3.1 using 14 000 is the max allowed settings for this level.
Using 2400 will restrict the choices the rate control of the encoder can make, and thus might force the encoder to use higher quantization values than necessary to be level compliant.

XMedia Recode probably uses 2400, since:
a. they assume that most SD content encoded doesn't use high bit rates anyway (if your encode is ~800kbit/s setting a max of 2400 usually is fine
b. the result will be easier to decode (since bit rate fluctuation is more restricted) for really old hardware

=> Personally, I would stick with the max allowed value unless I got specific hardware which does not even support the full 3.1 level restrictions.

afaik. setting one vbv value to 0 will disable all vbv restrictions.

Cu Selur

So should I stick with the default settings of xmedia recode using 2400, or do I need to increase it up to 14000?

[Selur]

That depends on what the average bit rate of your content is and whether it contains lots of 'action'. For content with action your usually want to allow stronger bit rate fluctuations than for something like watching someone holding a PowerPoint presentation,...
If your content leans into the normal more action packed region and your average bit rate is above 1200kBit/s I would increase from 2400 otherwise its fine.

[yomle]

[QUOTE=yomle;2709631]

=> Personally, I would stick with the max allowed value unless I got specific hardware which does not even support the full 3.1 level restrictions.


Cu Selur

So, by this, did you mean to set it to 14.000?

[Selur]

I would set it to 14000, but like I explained it depends on what your content and your goals are.