[Feature] Transcode setting of average bitrate

[Goodwu]

I have searched the existing feature requests to make sure this is not a duplicate request.

• Yes

The feature

The transcoding output quality is very low on J3455 with HW encoding on.
The average bitrate is lower then 500kb/s.
There's no effect by setting max bitrate to higher value. But set averate bitrate to higher value by command line "-b:v" have effect.

Platform

• Server
• Web
• Mobile

[Goodwu]

Is this a bug?
I look into the code and I see some other encoders like NV and VAAPI have -b:v argument but Qsv does not.

[suurt8ll]

I think qsv passes -b:v 1k always by default if it's not set in the arguments for some reason. -b:v 1k -maxrate 4500k -global_quality:v 23 all together trigger QVBR not ICQ.

[suurt8ll]

OK in the meantime I'll use this workaround for the 1k limit issue:

1. Set Maximum bitrate to 0 in System Settings
2. Choose Constant rate factor
3. In Transcode policy select All videos

This works, but effectively loses user the ability to transcode videos based on max bitrate policy. All videos policy will waste space but in my case it's not a huge problem because I do not store that much videos.

If you want me to run other commands on my hardware for debugging I'm happy to help out! Thanks for your work!

[mertalev]

What rate control mode does it use if you set -b:v 0 -maxrate 4500k -global_quality:v 23? Maybe we just need to make sure we add -b:v 0 if we're adding -maxrate.

[suurt8ll]

[h264_qsv @ 0x563132db0f40] Using input frames context (format qsv) with h264_qsv encoder.
[h264_qsv @ 0x563132db0f40] Encoder: input is video memory surface
[h264_qsv @ 0x563132db0f40] Use Intel(R) oneVPL to create MFX session with the specified MFX loader
[h264_qsv @ 0x563132db0f40] Using the constant quality with VBR algorithm (QVBR) ratecontrol method
[h264_qsv @ 0x563132db0f40] Error initializing the encoder: invalid video parameters (-15)
[vost#0:0/h264_qsv @ 0x563132d518c0] Error initializing output stream: Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height
[AVIOContext @ 0x563132dd7c00] Statistics: 0 bytes written, 0 seeks, 0 writeouts
Terminating demuxer thread 0
[AVIOContext @ 0x563132d52c40] Statistics: 1386984 bytes read, 2 seeks
Conversion failed!

• -b:v 0 -maxrate 4500k -global_quality:v 23 chooses QVBR but fails, see provided log above.
• -b:v 0 -maxrate 4500k chooses VBR but also fails in the same way.
• -b:v 0 chooses CBR but same failure

-b:v 0 -global_quality:v 23 is the only combo where bitrate can be 0 and command does not fail (this uses ICQ). In fact -b:v seems to have 0 importance in this configuration. It does not change the resulting bitrate, whatever number i pick.

Only when -maxrate is introduced QSV picks QVBR rate control mode for some reason and starts behaving weirdly.

[mertalev]

Thanks for testing! It's a shame that it doesn't work. We might have to handle it like VAAPI and switch to VBR when the max rate is set.