Why this ffmpeg mp4/mkv/wmv/flv/avi to webm command line with cuda is as slow as with CPU?

Question

im playing with my video files, I want to convert them from mp4, mkv, wmv, avi, flv, mov... to webm.

So I have written this:

for file in *
    do   
if [ -f "$file" ]
    then     filename="${file%.*}"
    ../ffmpeg -hwaccel nvdec -hwaccel_device 0 -hwaccel_output_format cuda -i "$file" -c:v vp9 -b:v 0 -crf 31 -c:a libvorbis "$filename".webm
fi
done

As shown, I have compiler my own ffmpeg binary, with those options:

./configure --enable-gpl --enable-libx264 --enable-nonfree --enable-cuda-nvcc --enable-libvpx --enable-vaapi --enable-libvorbis  --enable-libnpp --extra-cflags=-I/usr/local/cuda/include --extra-ldflags=-L/usr/local/cuda/lib64

It works, but, with CPU I got speed 0,1x and with cuda... almost the same.

My CPU? 11th Gen Intel(R) Core(TM) i7-11800H

My GPU? GeForce RTX™ 3060 mobile

Filesize? 300-3000mb (same speed with any)

Is there anything I could do? (I also tried vp9_vaapi, getting

Impossible to convert between the formats supported by the filter 'Parsed_null_0' and the filter 'auto_scale_0'
Error reinitializing filters!
Failed to inject frame into filter network: Function not implemented

Any clue? Or do I have to give up?

Thanks

Answer 1

Well, after some tests, the bests results were obtained using

-c:v libvpx-vp9 -cpu-used 8 -deadline realtime 

speed increased from 0,05x to 1,12x slow, but, good enough.

Quality is good for me.