i’m building a ffmpeg-wrapper these days to make my own life easier with ffmpeg. the project includes a cli, express server and mcp server.

i was adding a command feature for video in which my agent ran a command like this:

ffmpeg -f lavfi -i anullsrc -c:a pcm_s16le "ffkity-silence-test.wav"

and that single command quietly created a 93 gb file on my mac.

anullsrc is a synthetic audio source. if you don’t provide a duration (-t) or another stopping condition (-shortest with a finite input), it can run effectively forever.

outputting to wav with pcm_s16le means uncompressed audio, so disk usage grows very fast. the biggest issue wasn’t just space usage. it was how quietly this happened

file written under /private/tmp, so not immediately visible in normal workflows. i only noticed after disk space started collapsing and daisy disk showed huge hidden/private usage.

i fixed it by:

• deleting the giant tmp file
• adding hard safety checks in my wrapper so this class of mistake is less likely to ship
• testing the existing commands for such behaviours.

correct command:

ffmpeg -f lavfi -i anullsrc=r=48000:cl=stereo -t 5 -c:a pcm_s16le /tmp/silence-5s.wav