What you should know
Turning an MP4 into an MP3 means pulling the soundtrack out of a video: the picture track is ignored, and only the audio track is read and encoded as MP3. It is the easiest way to keep a talk, a filmed podcast or a song to listen to without a screen.
The audio inside an MP4 is almost always AAC, an already compressed format. Moving to MP3 is therefore a re-encode: FileXvert does it at 192 kb/s by default, a bitrate at which the difference from the source is inaudible for most listening.
Strengths
- The result plays on every player, car stereo and speaker
- Far lighter than the video, since the picture is dropped
- Fast: the video track is never decoded
- Adjustable bitrate: 192, 128 or 96 kb/s depending on the size reduction
Limitations to know
- Re-encoding already compressed audio: slight loss is unavoidable
- Only one audio track is kept from a multi-language video
- Subtitles and chapters from the video are not carried over
- A video without an audio track produces nothing usable
When to use it
Convert when only the sound matters: listening to an interview on a walk, keeping the music from a clip, sharing a voice recording filmed on a phone. If you need the best possible fidelity for audio editing, choose WAV instead, which avoids a second round of compression.
Quality, size and compatibility
Without size reduction the MP3 is encoded at 192 kb/s, so one hour of audio weighs about 85 MB. The balanced setting drops to 128 kb/s, plenty for speech; the smallest size setting uses 96 kb/s and is best kept for spoken recordings.
Frequently asked questions
- Does MP4 to MP3 keep the sound quality?
- Almost: the MP4's AAC audio is decoded and re-encoded to MP3 at 192 kb/s. The loss exists in theory but is not noticeable in ordinary listening.
- Is my video uploaded to a server?
- No. FFmpeg extracts the audio directly in your browser: the video never leaves your device, which matters for a private recording.
- Can I extract the audio from a MOV or MKV the same way?
- Yes, any video with an audio track (MP4, MOV, MKV, AVI, WebM) can become an MP3, WAV, FLAC, AAC, OGG or M4A file.