Build a small FFmpeg fixture set with variable frame rate, rotation metadata, multiple audio tracks, subtitles, and an unusual codec. Run the exact conversion command you intend to automate, then inspect the output with ffprobe and watch key segments for sync and quality.
Pin the FFmpeg build and document codec availability. Never overwrite the original until checks pass. A zero exit code does not prove the output kept the correct tracks, duration, color, or subtitles.
Akousa