libav provides a test suite:

The version included in Debian Jessie runs but has lots of errors. You can run it after debuild using:

# 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

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 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.