The one-line difference
MP4 is a video file — it carries the moving picture and the sound together. MP3 is an audio-only file — it strips out the video and keeps just the sound. If you want to watch or re-edit the clip, you need MP4. If you only care about the music, voiceover, podcast or sound effect, MP3 is smaller and drops straight into an audio app.
When to choose MP4
Pick MP4 whenever the visuals matter: reposting a Reel or Short, building a compilation, adding captions, or archiving a clip to watch later. It's also the safe default when you're not sure — you can always extract the audio from an MP4 afterward, but you can never add video back into an MP3. MP4 plays natively on every phone, computer and TV.
When to choose MP3
Pick MP3 when the sound is the whole point: a trending song, a lecture or interview, a meditation track, or a sample for your own video. Because there's no picture, MP3 files are a fraction of the size, so they're faster to download and kinder to your storage — ideal for building a playlist or feeding audio into an editor. The converter below turns any supported video link into a clean MP3.
Quality, size and rights
Neither format invents quality it doesn't have — both can only be as good as the source upload, so start from the original when you can. As a rule of thumb: choose MP4 for anything you'll watch or edit, MP3 for anything you'll only listen to. And whichever you pick, only download content you have the right to reuse and respect each platform's terms of service.