6 min read
Extracting audio from video: FFmpeg commands and a browser alternative
Copy the stream, do not re-encode it. The three commands worth remembering, and what to do when you cannot install anything.
Extracting audio from a video file should be a copy operation, not a conversion. If the audio track is already what you need, re-encoding it only loses quality and time.
Copy the stream untouched
The safest command demuxes the existing audio without decoding it. The output container has to support the codec, so AAC from an MP4 goes into an M4A, not a WAV.
- ffmpeg -i input.mp4 -vn -acodec copy output.m4a
- -vn discards the video stream.
- -acodec copy passes the audio through bit for bit.
Convert to WAV for editing
Post production wants uncompressed PCM. Ask for it explicitly rather than letting FFmpeg choose, and state the sample rate only if you genuinely want a conversion.
- ffmpeg -i input.mov -vn -c:a pcm_s24le output.wav
- pcm_s24le gives 24 bit little endian PCM, the film standard.
- Add -ar 48000 only when the source is not already 48 kHz.
- Add -map 0:a:1 to pick the second audio stream when a file carries several.
Check what is inside first
Before extracting, read the streams: ffprobe -show_streams input.mp4 reports the codec, sample rate, channel layout and bitrate. Extracting blind is how people end up resampling 48 kHz material to 44.1 kHz without noticing.
When you cannot install FFmpeg
On a locked down edit workstation or a client machine, installing command line tools is often not an option, and uploading unreleased footage to a web converter is worse. The extractor on this site reads the container directly in the browser, reports the true sample rate, bit rate and codec, and writes a WAV or AIFF at the settings you choose. Nothing is uploaded.