Default poor libvpx quality (master branch)

[apiraino]

So, now wf-recorder defaults to the VP8 encoder instead of h264.

I'm running wf-recorder compiled from 460d454 and I observe that the defaults for the libvpx codec produce a low quality ("blockier") video while defaults for h264 produced a better video, example:

wf-recorder -a --log

The low quality of the video is also explained by this warning

[libvpx @ 0x7fbd240022c0] Neither bitrate nor constrained quality specified, using default CRF of 32 and bitrate of 256kbit/sec

As per this issue, I tried to tweak the quality with this command but unfortunately the previous warning persists:

wf-recorder -a -pqmin=0 -pqmax={tried from 32 to 50} --log

How can this codec be configured for better quality?

cc @Conan-Kudo that authored #198 and hopefully more knowledgeable. Can you please share a configuration for the new default codec that results in a good video quality?

thanks

[ammen99]

As an alternative, you can always choose another codec with -c (vp9, libx264 are probably better alternatives if your ffmpeg and video players support them, which is usually the case)

[apiraino]

@ammen99 thanks for the tip. The thing is that tweaking VP8 or VP9 is tricky, I'm trying to force wf-recorder to use the parameters I pass from the command line, no luck for now. Examples:

# error
wf-recorder -a -c libvpx-vp9 -pminrate=500K -pmaxrate=500K -pb:v=500K
# params ignored?
wf-recorder -a -c libvpx-vp9 -pcrf=30 -pb:v=0
# params ignored?
wf-recorder -a -c libvpx-vp9 -pcrf=30 -pb:v=2000K

In addition VP9 needs some additional params (-pdeadline=realtime -pspeed=8) to reduce the lag when the encoder is crunching frames (also mentioned in #80 and here).

I should probably also mention that previously wf-recorder (using the default h264 codec) produced the following file:

$ wf-recorder -a -c libx264
...
Setting codec option: crf=20
Setting codec option: preset=ultrafast
Setting codec option: tune=zerolatency

# Bitrate video
Bit rate                                 : 49.4 Gb/s
Maximum bit rate                         : 2 424 kb/s
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive

which was absolutely adequate. These are the values I'm more or less aiming for.

[Conan-Kudo]

What KPipeWire does is set threads=4, preset=ultrafast, tune-content=screen, deadline=good. That's probably a good way to go.

https://github.com/KDE/kpipewire/blob/cda131c6485aa6c43d5132251566a798c64b50f9/src/pipewirerecord.cpp#L277-L280

[apiraino]

ok, after some more tests here's a good version of wf-recorder using VP9:

wf-recorder \
     # use the VP9 codec
    -c libvpx-vp9 \
    # fastest encoding possible
    -p deadline=realtime -p speed=8 -p threads=4 \
    # tune the video quality
    -p preset=ultrafast -p tune-content=screen

Worth noticing that the combination of VP9 codec + audio with Opus does not work. Example, adding the following to the previous command:

-a alsa_input.pci-0000_00_1f.3.analog-stereo --audio-codec=libopus \

no idea why, with libvorbis it works. I guess it's something on ffmpeg? 🤷‍♂️

Thanks everyone for the suggestions.

[Conan-Kudo]

Do we want to try to update the wf-recorder defaults for this?

[ammen99]

Do we want to try to update the wf-recorder defaults for this?

If it improves the quality with default settings, it makes sense, yes.

[Conan-Kudo]

Here's a go at that in #216 based on @apiraino's suggestions and checking the ffmpeg code to ensure we don't use removed/deprecated options.