VP8

VP8 is an open-source and royalty free codec developed by the Alliance for Open Media (AOMedia), a non-profit industry consortium. It will only encode to 8-bit 4:2:0 using the webm container. It is possible to get a similar quality to h264, but not typically at the same compression ratio. It is recommended that you consider VP9 which is a considerably better codec. VP8 does support an alpha channel (via the yuva420p pixfmt).

General ffmpeg info on VP8 is here, and on the encoder in general https://www.webmproject.org/docs/encoder-parameters/.

VP8 has browser support in:

Chrome.
Edge
Firefox
Opera

VP8 is supported by mkv and webm containers, no support exists for mov or mp4.

libvpx

libvpx has a limited range of pixel formats: yuv420p yuva420p

Example encoding:

ffmpeg -r 24 -start_number 1 -i inputfile.%04d.png -frames:v 200 \
    -c:v libvpx -crf 20 -b:v 200M -pix_fmt yuv420p \
    -qmin 0 -qmax 50 -quality good -speed 4 \
   -sws_flags spline+accurate_rnd+full_chroma_int \
   -vf "scale=in_range=full:in_color_matrix=bt709:out_range=tv:out_color_matrix=bt709" \
   -color_range tv -colorspace bt709 -color_primaries bt709 -color_trc iec61966-2-1  \
     -y outputfile.webm

Recommended Flags

-crf 20 -quality good -b:v 200M  -speed 4

-crf 20	This is the constant quality rate factor, controlling the default quality, similar to h264. The range is a little different to h264, so you may need to test.
-quality good	May require additional testing, but so far switching to -quality best increased the duration, but didn’t increase the VMAF score (which is already pretty high with these values of crf).
-b:v 200M	Unlike with h264, and vp9 you need to set the bit rate, but you can set it to a high number, and this is the max it would be.
-speed 4	It sets how efficient the compression will be. Unless you are using -quality best, this doesnt seem to have a setting for