Do the transcoding quality settings actually work?

[flo f]

I changed CRF for H264 to a different value but I don't see where it would be reflected in the call to ffmpeg. Does this setting actually do anything? And how about the encoding preset? I have it on Ultrafast but it doesn't seem to make any difference to fast.

Code:

/usr/lib/jellyfin-ffmpeg/ffmpeg -analyzeduration 200M -init_hw_device vaapi=va:,kernel_driver=i915,driver=iHD -init_hw_device qsv=qs@va -init_hw_device opencl=ocl@va -filter_hw_device ocl -autorotate 0 -canvas_size 1920x1080 -i file:"/mnt/data/usenet/library/movies/movie.mkv" -map_metadata -1 -map_chapters -1 -threads 0 -map 0:0 -map 0:2 -map -0:0 -codec:v:0 h264_qsv -low_power 1 -preset 7 -look_ahead 0 -b:v 6616000 -maxrate 6616000 -bufsize 13232000 -g:v:0 72 -keyint_min:v:0 72 -filter_complex "[0:3]scale=s=1920x1080:flags=fast_bilinear[sub];[0:0]setparams=color_primaries=bt2020:color_trc=smpte2084:colorspace=bt2020nc,scale=trunc(min(max(iw\,ih*a)\,1920)/2)*2:trunc(ow/a/2)*2,format=yuv420p[main];[main][sub]overlay=eof_action=pass:shortest=1:repeatlast=0" -start_at_zero -codec:a:0 libfdk_aac -ac 2 -ab 384000 -af "volume=2" -copyts -avoid_negative_ts disabled -max_muxing_queue_size 2048 -f hls -max_delay 5000000 -hls_time 3 -hls_segment_type mpegts -start_number 0 -hls_segment_filename "/var/lib/jellyfin/transcodes/d94ee3b60f37f3a8af08debcb4e2332b%d.ts" -hls_playlist_type vod -hls_list_size 0 -y "/var/lib/jellyfin/transcodes/d94ee3b60f37f3a8af08debcb4e2332b.m3u8"

[Efficient_Good_5784]

Are you using HWA (GPU transcoding)? Looks like you're using either VAAPI or QSV from the log you shared.

In my experience, those encode settings only apply to CPU transcoding.

[gnattu]

In my experience, those encode settings only apply to CPU transcoding.

Yes. These settings only applies to CPU encoders.

These CRF settings typically have no effect on hardware encoders because:

• The hardware vendor's own metrics, such as "CQ," have different interpretations across vendors, and they differ from the CRF used in software encoders.
  
• Most of the time, we will have a bitrate limit that overrides the constant quality setting on hardware encoders. The actual override policy is vendor-specific.
  

If you want to trade off quality for speed, you can select an Encoding Preset. We have some internal mappings from these presets to hardware vendor-defined quality levels.