Guides · updated October 22, 2026

ffmpeg MP4 to MP3

The exact ffmpeg flags for extracting MP3 from MP4, a batch loop, and an honest comparison with the browser converter.

Tested: 22 October 2026 · ffmpeg 8.0.1 · MP4/AAC and MOV/PCM fixtures

Short answer

The command is ffmpeg -i input.mp4 -vn -c:a libmp3lame -b:a 192k output.mp3. -vn drops the video, -c:a libmp3lame selects the MP3 encoder, and -b:a sets a constant bitrate. Use -q:a 2 instead of -b:a for VBR. The browser converter is the same job without installing ffmpeg.

The one-liner

ffmpeg -i input.mp4 -vn -c:a libmp3lame -b:a 192k output.mp3

Flags, in order:

-i input.mp4 — the source file.
-vn — no video output. The picture is skipped, not re-encoded.
-c:a libmp3lame — use the LAME MP3 encoder.
-b:a 192k — constant bitrate at 192 kbps.
output.mp3 — the target. The extension selects the MP3 muxer.

For VBR instead of CBR:

ffmpeg -i input.mp4 -vn -c:a libmp3lame -q:a 2 output.mp3

LAME’s -q:a scale runs from 0 (best) to 9 (smallest). 2 is a common music setting, roughly 170–210 kbps depending on the material. The browser converter does not offer VBR; ffmpeg is the route when you want it.

Common variations

Pick the second audio track:

ffmpeg -i input.mp4 -vn -map 0:a:1 -c:a libmp3lame -b:a 192k output.mp3

Force 44.1 kHz stereo:

ffmpeg -i input.mp4 -vn -c:a libmp3lame -b:a 192k -ar 44100 -ac 2 output.mp3

Trim before encoding:

ffmpeg -ss 00:01:30 -to 00:04:00 -i input.mp4 -vn -c:a libmp3lame -b:a 192k output.mp3

Batch a folder:

for f in *.mp4; do
  ffmpeg -i "$f" -vn -c:a libmp3lame -b:a 192k "${f%.mp4}.mp3"
done

What ffmpeg will not do for you

It will not make MP3 lossless. The AAC track is decoded and re-encoded; the second generation is real.
It will not choose the right bitrate for you. Inspect the source first:

ffprobe -v error -select_streams a:0 \
  -show_entries stream=codec_name,bit_rate,sample_rate,channels \
  -of default=nw=1 input.mp4

It will not fix a broken file. A truncated MP4 is a truncated MP4.

When the browser is the better tool

Situation	Better route
One file, no install	Browser
You want to see the audio track and duration first	Browser
A folder of files, unattended	ffmpeg
VBR or a specific filter chain	ffmpeg
A codec the browser cannot decode	ffmpeg
A machine where you cannot install software	Browser

The browser converter is not a replacement for ffmpeg. It is a smaller tool for the common case: one file, no account, no upload, a visible result in a few seconds. ffmpeg is the professional route when you need control or scale.

A note on “no upload”

Both routes are local. ffmpeg reads the file from disk and writes the output next to it. The browser reads the file through the File API and writes a Blob. Neither one needs a server. The difference is where the CPU work happens and how much control you have over the encoder settings.

FAQ

What does -vn do?

It disables video output. ffmpeg reads the MP4, ignores the picture, and writes only the audio stream. Without -vn, ffmpeg would try to include a video stream, which an MP3 container cannot hold.

Can I copy the AAC stream into MP3 with -c:a copy?

No. -c:a copy copies the encoded packets unchanged; AAC packets cannot live in an MP3 container. To keep the AAC stream, output M4A instead: ffmpeg -i input.mp4 -vn -c:a copy output.m4a. MP3 requires re-encoding with libmp3lame.

How do I select the second audio track?

Add -map 0:a:1 before the output. Use ffprobe -show_streams input.mp4 to see which audio streams exist. The first audio stream is 0:a:0, the second is 0:a:1.

Is ffmpeg faster than the browser?

Native ffmpeg is usually faster, especially for long files, because it is not limited by the browser's JavaScript and WebAssembly overhead. The browser route avoids an install and gives you a visual check before converting.

How do I batch convert a folder?

On macOS or Linux: for f in *.mp4; do ffmpeg -i "$f" -vn -c:a libmp3lame -b:a 192k "${f%.mp4}.mp3"; done. On Windows PowerShell, use Get-ChildItem *.mp4 | ForEach-Object { ffmpeg -i $_.FullName -vn -c:a libmp3lame -b:a 192k ($_.BaseName + '.mp3') }.