Run ffmpeg, a WASM build downloaded on demand.

Synopsis

ffmpeg [global-opts] -i input [input-opts] ... output [output-opts]

Description

A WebAssembly build of ffmpeg. Common flags pass through unchanged. Inputs and outputs are resolved against the current VFS working directory. The first run downloads roughly 31 MB of ffmpeg-core; subsequent runs reuse the cached copy.

Options

-f concat -safe 0 -i list.txt Concatenate files listed in list.txt (paths resolved relative to the list file's directory; the concat: protocol form is not supported, use -f concat instead).

-f avfoundation -i "0" Capture from a webcam/microphone, avfoundation-style (numeric index selects a device from enumerateDevices()).

-warmup MS Photo mode: ms to wait for auto-exposure to settle before grabbing a frame (default 1500).

-exact_size Use exact:{w,h,frameRate} capture constraints instead of ideal:.

Examples

$ C

o

$ G

r

$ ffmpeg -i in.mp4 -af loudnorm=print_format=json -f null /dev/null

Analyze loudness without writing an output file.

Notes

Output '-' requires -f null (stdout is not emulated); bare /dev/null is accepted and gets -f null injected, since MEMFS has no /dev/null. The browser prompts for camera/mic permission on first capture. Output options like -c:v, -crf, -vf, or a mismatched extension trigger a post-capture WASM transcode pass.

See Also

ffprobe, convert, pdftoppm