libav provides a test suite:
https://libav.org/fate.html

The version included in Debian Jessie runs but has lots of errors.
You can run it after {{{debuild}}} using:
{{{
cd debian-extra-shared/
# add V=1 for verbose output
make fate-rsync SAMPLES=/home/build/fate-suite/
LD_LIBRARY_PATH=libavcodec:libavdevice:libavfilter:libavformat:libavresample:libavutil:libswscale \
  make -k fate \
    SAMPLES=/home/build/fate-suite/ \
  2>&1 | tee tests.log
grep -c ^TEST tests.log  # 2019-11-05: 1823
grep -c ^make:.*Error tests.log # 2019-11-05: 141
}}}

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libav is a fork of ffmpeg.

Bugs may be found by oss-fuzz against the ffmpeg project, which uses a specific in-process fuzzing target such as [[https://github.com/FFmpeg/FFmpeg/blob/master/tools/target_dec_fuzzer.c|target_dec_fuzzer.c]].

It's not clear if this fuzzing target can be ported to libav to help determine reproduce ffmpeg vulnerabilities in libav.