https://ayosec.github.io/ffmpeg-filters-docs/2.5/Sinks/Video/nullsink.html
nullsink - FFmpeg 2.5.11 / Sinks / Video
ffmpegsinksvideo
https://ffmpeg.org/doxygen/4.1/vsink__nullsink_8c.html
FFmpeg: libavfilter/vsink_nullsink.c File Reference
ffmpegcfile