building ffmpegsumo is a PITA, you need to fight with chromium’s build system, but so far this seems to work:
GYP_DEFINES=”proprietary_codecs=1 target_arch=x64 branding=Chrome” ./build/gyp_chromium build/all.gyp
–> use the hacks to produce the ffmpegsumo and ffmpeg_yasm ninja files <–
./depot_tools/ninja -v -j4 -C out/Release ffmpegsumo
it didn't work for me, not that nor generate_gyp.py