Question about StaxRip

[Hossein Enr7que]

Hi guys. I am using Bitrate mode to encode videos with x264 and x265 codec with StaxRip.
but today after encoding a movie, i am feeling that maybe the quality is not very good.
Do the bitrate mode is good for encoding?
Do this mode have similar quality with crf in same bitrate?
and if no the quality is not same, so which one is better? Bitrate, Quantizer, Quality, 2pass, 3pass?
and the last question if i want my video have a bitrate between 2800 to 3400 in crf mode, which number should i use?
thank you so much.

[jagabo]

The definition of bitrate is:

bitrate = size / running_time

A little algebraic manipulation gives:

size = bitrate * running_time.

So with bitrate based encoding you are choosing the size of the video stream. But you don't know the exact resulting quality.

CRF (quality) based encoding is the flip side of the coin: you choose the quality of the video, but you don't know the resulting size.

There are two types of bitrate based encoding: constant bitrate and variable bitrate. Constant bitrate uses the same bitrate for the entire video. A still shot of a bowl of fruit will get just as much bitrate as a complex action scene. This can be very wasteful. Variable bitrate uses different bitrates for difference scenes. Scenes that need a lot of bitrate (like the high action scene) get it. Scenes that don't need a lot of bitrate (the still shot) get less.

All else being equal, variable bitrate results in better quality than constant bitrate.

There are two types of variable bitrate: 1 pass and 2 (or more) pass.

All else being equal, 2-pass VBR delivers better quality than single pass VBR.

With x264 and x265 2-pass VBR delivers almost exactly the same quality as CRF encoding -- when the resulting size is the same and all else is equal. So which do you choose?

If you have size constraints you want to use 2-pass VBR. For example, if you want to put a 2 hour movie on a 4 GB thumb drive at maximum quality you use 2-pass VBR and tell the encoder to generate a 4 GB file (well... slightly less because you need to fit the audio and container overhead too). You could do this with CRF encoding but you would have to make several encodings with different CRF values to finally get the size you want. So it makes much more sense to use 2-pass VBR.

If you care more about the quality of the video, and don't care about the exact size, use CRF encoding. Once you are familiar with the codecs you'll know what CRF value will deliver the quality you want. With x264 CRF values around 18 and the "slow" preset will deliver a video that's pretty close to the source video when viewed at normal playback speed.


There's another type of constant quality encoding -- constant quantizer (QP). This is constant quality in a mathematical sense. CRF is constant quality but takes into account what is more or less visible to the human eye. CRF uses bitrate more efficiently than QP. So you almost always want to use CRF.

[Hossein Enr7que]

The definition of bitrate is:

bitrate = size / running_time

A little algebraic manipulation gives:

size = bitrate * running_time.

So with bitrate based encoding you are choosing the size of the video stream. But you don't know the exact resulting quality.

CRF (quality) based encoding is the flip side of the coin: you choose the quality of the video, but you don't know the resulting size.

There are two types of bitrate based encoding: constant bitrate and variable bitrate. Constant bitrate uses the same bitrate for the entire video. A still shot of a bowl of fruit will get just as much bitrate as a complex action scene. This can be very wasteful. Variable bitrate uses different bitrates for difference scenes. Scenes that need a lot of bitrate (like the high action scene) get it. Scenes that don't need a lot of bitrate (the still shot) get less.

All else being equal, variable bitrate results in better quality than constant bitrate.

There are two types of variable bitrate: 1 pass and 2 (or more) pass.

All else being equal, 2-pass VBR delivers better quality than single pass VBR.

With x264 and x265 2-pass VBR delivers almost exactly the same quality as CRF encoding -- when the resulting size is the same and all else is equal. So which do you choose?

If you have size constraints you want to use 2-pass VBR. For example, if you want to put a 2 hour movie on a 4 GB thumb drive at maximum quality you use 2-pass VBR and tell the encoder to generate a 4 GB file (well... slightly less because you need to fit the audio and container overhead too). You could do this with CRF encoding but you would have to make several encodings with different CRF values to finally get the size you want. So it makes much more sense to use 2-pass VBR.

If you care more about the quality of the video, and don't care about the exact size, use CRF encoding. Once you are familiar with the codecs you'll know what CRF value will deliver the quality you want. With x264 CRF values around 18 and the "slow" preset will deliver a video that's pretty close to the source video when viewed at normal playback speed.


There's another type of constant quality encoding -- constant quantizer (QP). This is constant quality in a mathematical sense. CRF is constant quality but takes into account what is more or less visible to the human eye. CRF uses bitrate more efficiently than QP. So you almost always want to use CRF.

thanks. your information really helped me. thank you so much