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MP4, MOV, WebM, GIF, MP3: what’s the difference, and which video tool do you need?

A clip plays fine on your phone but gets rejected by a work laptop or an upload page, or a three-minute video blows past an email attachment limit. Most of these problems make sense once you know how a video file is put together and what decides its size, so here are the basics and a quick way to pick the right tool.

A closer look

MP4, MOV and WebM are containers: wrappers that hold a video track and an audio track in sync. The picture and sound inside are compressed with codecs. An MP4 usually carries H.264 or HEVC video with AAC audio, while a WebM carries VP8 or VP9 video with Opus audio. iPhones on the default “High Efficiency” setting record HEVC inside a MOV file, and any PC or app that can’t decode HEVC will refuse it, whatever the file is called. WebM, which screen recordings often produce, tends to get stuck on upload pages that expect MP4.

Size comes down to bitrate, the data per second, multiplied by length. 720p at Medium in Compress video works out to roughly 18.7 MB per minute with audio, and 1080p has 2.25 times the pixels, so it needs roughly that much more data to look as sharp. Audio at 128 kbps takes less than 1 MB a minute, so squeezing the sound barely helps. MP3 and M4A (AAC) are lossy, WAV is uncompressed at around 10 MB a minute in stereo, and FLAC is lossless compression that leaves the sound untouched. GIF has no audio; it strings together 256-color pictures, so a few seconds often outweigh the same scene as MP4.

How to use it

• Name the problem first. Won’t open: format. Won’t send: size. Only need the sound: extraction. Something to hide or add: an edit.
• If it won’t open, use Convert formats or MOV to MP4. When the codecs already suit MP4, the data is moved into a new container without re-encoding, so it takes seconds with no quality loss. The codec stays the same, though: HEVC is still HEVC inside the MP4.
• If it’s too big, cut it down with Trim video first; it doesn’t re-encode, so quality is untouched and size drops with length. Still too large? In Compress video, tick Hit a target file size and type the limit, such as “20MB”.
• For just the audio, pick MP4 to MP3 or MP4 to M4A. When a phone video’s soundtrack is AAC, M4A pulls it out as is, without compressing it again. Polish it with the Audio cutter and Remove noise.

When it helps

Common snags

Tip Every re-encode costs a little quality, so compress once, at the very end, and keep the original until you’ve checked the result.