Constant Quality vs Avg Bitrate at equal bitrates

General questions or discussion about HandBrake, Video and/or audio transcoding, trends etc.
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EhronW
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Joined: Sat Jul 25, 2020 2:08 pm

Constant Quality vs Avg Bitrate at equal bitrates

Post by EhronW »

I am in the process of converting all of my movies over to a smaller bitrate to allow for streaming on my Emby server using my limited bandwidth. To avoid the cpu strain of constant transcoding, I have used HB to convert all the movies to limit the bitrate, which has worked great. On all of the guides and advice I have read, Constant Quality is superior to setting an Avg Bitrate, as well as being much faster to encode. My question is, there are times when I have to go through and change the Constant Quality setting and reencode multiple times to get to my target bitrate limit. If I am already using CQ to get down below a bitrate such as 7000kbps, would there still be a quality difference if I were to have just set that bitrate using the Avg Bitrate setting in the first place? Thanks.

rollin_eng
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Re: Constant Quality vs Avg Bitrate at equal bitrates

Post by rollin_eng »

If you want a certain quality use CQ, if you want a certain bitrate use ABR.

A CQ encode that is 7000 kbps will be the same as a 2 pass ABR at 7000 kbps.

Could you please post your HB logs, instructions can be found here:

https://handbrake.fr/docs/en/latest/hel ... y-log.html

musicvid
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Re: Constant Quality vs Avg Bitrate at equal bitrates

Post by musicvid »

It's the other way around. Every source is different, so matching a bitrate will always give you a different quality.

If your home server has limited bandwidth, best thing is to limit vbv-maxrate, since that is what causes stuttering.

mduell
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Re: Constant Quality vs Avg Bitrate at equal bitrates

Post by mduell »

You should be using vbv to cap bitrate peaks for streaming, and letting the constant RF do what it needs otherwise.

EhronW
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Joined: Sat Jul 25, 2020 2:08 pm

Re: Constant Quality vs Avg Bitrate at equal bitrates

Post by EhronW »

Thanks for the replies. I'm not having problems with studdering or anything. I'm just trying to limit the bitrate so I'm not over-taxing my internet connection, and my NAS doesn't have to transcode all the time. I am fine with some variations in quality as long as it is all still decent.

EhronW
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Joined: Sat Jul 25, 2020 2:08 pm

Re: Constant Quality vs Avg Bitrate at equal bitrates

Post by EhronW »

mduell wrote:
Sat Jul 25, 2020 11:47 pm
You should be using vbv to cap bitrate peaks for streaming, and letting the constant RF do what it needs otherwise.
This sounds like how I would like to handle it, but I'm not familiar enough with how to use the vbv parameter. Could you point me in the direction of a relevant guide? How does vbv work alongside the constant RF? If I set the quality higher, does it simply not go any higher than what the bitrate allows?

mduell
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Re: Constant Quality vs Avg Bitrate at equal bitrates

Post by mduell »

VBV specifies a maximum bitrate and a buffer size. It will constrain bitrate spikes that constant RF would otherwise have during high motion/complexity/detail.

https://forum.doom9.org/archive/index.php/t-147460.html

musicvid
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Re: Constant Quality vs Avg Bitrate at equal bitrates

Post by musicvid »


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