Bitrate settings Media Coder

[ro2124]

Been using media coder for recoding large size MP4 file.
But not sure which setting is best for quality, perhaps someone could advise?

There are several settings under Bitrate

Average bitrate
Variable bitrate
Constant bitrate
Constant QP
2-pass
3-pass

And would file size increase much using highest quality setting, (whichever that may be from above list)

[smrpix]

And would file size increase much using highest quality setting, (whichever that may be from above list)

Almost certainly.

The best way to learn this is to take a short segment of your file say around 2 minutes with moderate to busy motion and try them all. See what happens to file size, picture quality and encoding times with the different options.

Ultimately, encoding is trial and experimentation anyway, so you may as well start now.

[ro2124]

@smrpix

Ok thanks for that and yes considered that option before using short segment.

But would be interested to know which of the stated bitrate settings would generally be regarded as best quality setting?

Also noticed another setting in Media Coder for Auto Bitrate what would that do?

[smrpix]

Of those options, constant bitrate and constant QP would generally deliver the worst. (I don't use Media Coder, but this is broadly applicable.)

Generally, higher bitrates give you more quality. Generally, non-constant bitrates allow the encoder to assign more appropriate bitrates to different sections of the encode depending on the complexity of the image - but they have various ways of achieving that. One way is to set a certain bitrate and let it be distributed over a certain number of encoding passes -- that way you can predict filesize. Another is to vary the bitrate depending on complexity in a single pass -- you don't know what the final filesize will be but you know more or less how it will look. Different files respond better to different methods of being encoded.

The best quality of course is to not re-encode at all. What is your ultimate goal?

[ro2124]

>What is your ultimate goal?

Basically to reduce the size of very large video files, some with bit rates as high as 5000. So reduced the rate to 3000 which should still give a pretty good qualitym which in fact it did -on some segments as you suggested.
And yes seems you are right the constant QP setting does seem to lower the quality a bit but all the files were acceptable. But I think I will go for variable bit rate be larger than constant QP but quality is very good

Anyway been a useful learning experience messing about with the different settings so thanks for all the info

[jagabo]

x264 with QP delivers whatever quality you ask for. It can even be lossless. What it doesn't do is give you the best quality at a particular files size.

The general rule is:

1) Use multipass bitrate based encoding when file size is of utmost concern. The encoder will give you whatever quality it can at that file size. But you don't know what that quality will be.

2) Or use CRF encoding when quality is of primary concern. You will get the quality you asked for but you don't know what the file size will be.

These are basically two sides of the same coin. If you perform a CRF encoding and end up with a particular bitrate, then encode a 2-pass encoding of the same source at that bitrate, the two videos will look nearly identical.