mpeg2_vaapi encoder "QP" parameter for CQP

[Andreas Håkon]

Summary of the bug:

When using the CQP Rate Control (-c:v mpeg2_vaapi -rc_mode CQP)
the current implementation only accepts the global_quality to configure it. This value is set using the "-q:v" option, but this value isn't in the common range 0-31 (in fact, 0.09 corresponds to 10, 0.1 to 11, etc.).

However, in the H.264 VAAPI encoder (h264_vaapi) the explicit parameter "QP" exists. And this value sets the GENERIC VAAPI ENCODER value of "explicit_qp". See:

​https://github.com/FFmpeg/FFmpeg/blob/f30fb5ef626140d6e286a22e4f5ca7e7f5b97c67/libavcodec/vaapi_encode_h264.c#L1258
​https://github.com/FFmpeg/FFmpeg/blob/f30fb5ef626140d6e286a22e4f5ca7e7f5b97c67/libavcodec/vaapi_encode_h264.c#L1236

So, only adding this "-qp" parameter to the MPEG2 VAAPI ENCODER, then it will enable the option to use the common 0-31 range with this encoder. In fact, a very small of new source lines are required. Just copy&paste!

Regards.

[jkqxz]

-global_quality:v

[Andreas Håkon]

Replying to jkqxz:

-global_quality:v

Hi,

I writed it in my report: -global_quality:v not uses the common range 1-31.

And for this reason h264_vaapi and others have -qp. Futhermore, the GENERIC implementation of the VAAPI encoder has the explicit_qp variable. And all vaapi encoders, EXCEPT the mpeg2 uses it. The request it's to copy&paste the four lines of code from vaapi_encode_h264.c to vaapi_encode_mpeg2.c

So I reopen the ticket as it's valid.
Regards.

[wenbin,chen]

According to here
​https://github.com/FFmpeg/FFmpeg/blob/2367affc2cea32f18a4d309835bed57adb1baa94/libavcodec/vaapi_encode_mpeg2.c#L522
you need to use "-i_qfactor","-i_qoffset","-b_qfactor" and "-b_qoffset" to set qp for I and B frame.

And according to here
​https://github.com/FFmpeg/FFmpeg/blob/2367affc2cea32f18a4d309835bed57adb1baa94/libavcodec/vaapi_encode.c#L1676
you need to use global quality to set qp for P frame.

thanks