MP4 or MP3, which format should you save in?
One keeps the picture, one keeps only the sound and a tenth of the space. Which is right depends entirely on what you plan to do with it.
The difference in one line
MP4 is a container holding picture and sound together. MP3 holds sound only, which is why the same clip lands roughly ten times smaller as an MP3.
Both come from the same source file, so choosing between them costs nothing but a different button.
When MP4 is the right pick
Anything you will actually watch: tutorials where the screen matters, recipes, footage you are editing, clips you want to keep as they were published.
It is also the safer archive format. You can always pull the audio out of an MP4 later, but you cannot put the picture back into an MP3.
MP4 plays on every phone, TV, console and editor without conversion, which is why platforms hand it out in the first place.
When MP3 is the right pick
Podcasts, interviews, lectures, sermons, audiobooks, music. Anything where the camera is pointed at a person talking or a static image.
An hour of speech is around 55 MB as a 128 kbps MP3, against several hundred megabytes as video. On a phone with a full storage bar that is the whole argument.
MP3 also plays in car stereos, older players and offline music apps that will not touch a video file.
Sizes to expect
Ten minutes of 1080p video sits roughly between 100 and 300 MB depending on motion.
The same ten minutes as a 192 kbps MP3 is about 14 MB.
Bumping an MP3 from 128 to 320 kbps roughly doubles it, and only pays off if the original audio was good and you are on real headphones.
What about MOV, WebM and M4A?
MOV is Apple's container. It behaves like MP4 and converts to it in seconds when something refuses to open it.
WebM turns up on some platforms and is fine in browsers but awkward in editors and on TVs. Convert it to MP4 if anything complains.
M4A is AAC audio, usually a touch better than MP3 at the same size, though MP3 still has wider support on old hardware.
Changing your mind later
Already saved the video and now only want the sound? The MP4 to MP3 tool strips the audio out without re-recording it, so nothing is lost twice.
Wrong container rather than wrong type? The converter switches between MP4, MOV, WebM and GIF locally in your browser.
If it is the words you are after rather than either file, the transcript generator turns the same clip into text you can search.