Convert MP4 to MP3

Why people turn MP4s into MP3s

A video file carries a picture you do not always need. Saving only the sound gives you a file a fraction of the size that plays anywhere music plays. Some everyday reasons:

• Lectures, webinars and sermons, to listen to on a walk or in the car with the screen off.
• Recorded calls and interviews, to send to a transcription service or keep as an audio record.
• Concerts, recitals and rehearsals you filmed on your phone, to play like any other song.
• Podcasts recorded on camera, published as audio as well.
• Voice-overs and sound for a slideshow, or a short clip to make into a ringtone.

Need only part of it? Convert the whole video first, then cut the MP3 down in the MP3 cutter. Want a different kind of file? MP4 to WAV and MP4 to M4A work the same way, and video to MP3 covers every other video format.

Choosing the MP3 quality

The sound in an MP4 is already compressed, usually as AAC. Turning it into MP3 cannot bring back detail that compression removed, so a 320 kbps MP3 made from a 128 kbps sound track is bigger, not better. As it is avoids that: it reads the bit rate of each video's sound and uses it, raised to 128 or lowered to 320 kbps when it falls outside that range. Mono sound gets half the bit rate at every setting, since one channel needs half the data. For an exact figure, More settings has Bit rate, from 64 to 320 kbps.

A whole folder of videos at once

Give Octoolo a folder and it gathers every video and sound file from it and from the folders within, three levels down, 500 at most per drop (Add more takes more after that). Because only the sound is converted, the picture is never decoded, and up to four files are worked on at once. Each line shows its progress, its speed and the time left, and Stop all ends the batch if you change your mind.

When the batch is done, a summary gives the number of files converted and their total size before and after, with Show in folder beside it. New files never replace old ones: a second “lecture.mp3” in the same place is saved as “lecture (2).mp3”. And if a video sits somewhere Octoolo cannot write, such as a read-only drive, its MP3 goes to an Octoolo folder inside your Music folder instead, and its line says so.

What comes along, and what stays behind

• Cover art. If the MP4 carries a cover picture, as music saved in MP4 form sometimes does, the MP3 keeps it. A frame of the video is never turned into a cover.
• Tags. A title, artist or album stored in the MP4 is carried into the MP3's tags.
• Surround sound. MP3 holds two channels at most, so 5.1 sound is mixed down to stereo.
• Very high sample rates. Sound recorded above 48 kHz comes out at 48 kHz, since a lossy format gains nothing above that.
• MP3 sound inside the MP4. It happens now and then, and As it is copies it straight across, untouched.
• Videos with no sound are flagged the moment you add them, with “This video has no sound to save.”

Octoolo cannot read copy-protected videos, such as purchased films; everything else FFmpeg opens is fair game.