If you’ve ever tried to upload a video somewhere and gotten an error, or opened a file your player refuses to touch, the format is almost always the reason. MP4, MOV, AVI, and WebM are all “containers” — wrappers that hold video and audio data — and each was built with a different priority in mind. Here’s what each is actually for, and which one to reach for by default.
What a “Container” Actually Is
MP4, MOV, AVI, and WebM aren’t compression methods themselves — they’re containers that package a video codec (like H.264 or VP9), an audio codec (like AAC or Opus), subtitles, and metadata into a single file. The container mostly determines compatibility — which devices and platforms will open the file at all — while the codec inside determines quality and file size. This is why format conversion, like AVI to MP4, is usually just repackaging, not a full quality overhaul.
MP4 — The Universal Default
MP4 (MPEG-4 Part 14) is the closest thing to a universal standard in video. It typically holds H.264 or H.265 video with AAC audio, and virtually every phone, computer, browser, game console, smart TV, and social platform accepts it without complaint.
- Compatibility: Excellent — plays natively everywhere
- File size efficiency: Very good, especially with H.264/H.265
- Best for: Uploading, sharing, streaming, archiving — basically everything
If you only remember one thing from this article: when you’re not sure what format to use, use MP4.
MOV — Apple’s Native Format
MOV is Apple’s QuickTime container, the default output from iPhones, iPads, and Mac editing apps like Final Cut Pro. A MOV file often contains the exact same H.264 or H.265 video as an MP4 — the difference is the wrapper and the metadata Apple’s ecosystem adds around it.
- Compatibility: Great on Apple devices, inconsistent elsewhere
- File size efficiency: Often large, especially ProRes footage
- Best for: Editing within Apple’s own ecosystem
This is exactly why so many people search for how to convert MOV to MP4 free right after recording on an iPhone — the file works perfectly on the phone itself but hits a wall the moment it needs to go anywhere else.
AVI — The Legacy Format
AVI (Audio Video Interleave) dates back to 1992, built by Microsoft for the Windows Media Player era. It’s a simple, older container structure that hasn’t kept pace with modern codec efficiency.
- Compatibility: Poor on modern devices — most phones and social platforms reject it
- File size efficiency: Weak by today’s standards
- Best for: Legacy compatibility only
If you’re holding onto old AVI files from a camcorder or an old screen recorder, how to convert AVI to MP4 free is almost always the right move — both for compatibility and to shrink the file down significantly.
WebM — Built for the Web
WebM is an open, royalty-free format developed by Google specifically for browser-based video. It typically uses the VP8/VP9 or AV1 video codec with Opus or Vorbis audio, and it’s what powers a lot of what you see embedded on the web without noticing — YouTube uses WebM extensively behind the scenes.
- Compatibility: Excellent in modern browsers, weaker in some older desktop software
- File size efficiency: Very good — comparable to or better than H.264 MP4
- Best for: Web embedding and streaming
Side-by-Side Comparison
| Format | Compatibility | File Size Efficiency | Best Use Case | Native Platform |
|---|---|---|---|---|
| MP4 | Excellent — plays everywhere | Very good | General use, sharing, uploading | Universal |
| MOV | Good on Apple, weak elsewhere | Often large (esp. ProRes) | Editing in Apple’s ecosystem | Apple / QuickTime |
| AVI | Poor on modern devices | Weak by modern standards | Legacy files only | Older Windows |
| WebM | Excellent in browsers | Very good | Web embedding, streaming | Web / Google |
So Which One Should You Actually Use?
If you’re not sure, use MP4. It’s the one format on this list that works almost everywhere without a second thought — every phone, every upload form, every social platform, every media player.
- Editing on a Mac in Final Cut Pro? Stay in MOV/ProRes until your final export, then convert to MP4 for delivery.
- Embedding video on a site you control and want the smallest file for fast page loads? WebM is worth the extra step.
- Received an old AVI file? Convert it to MP4 immediately — there’s no real downside.
In practice, most format questions resolve the same way: convert to MP4. Use AllMediaTools Video Converter to switch between any of these formats for free, then run the result through AllMediaTools Video Compressor if the file is still larger than you need.
The codec inside the container matters too — see our H.264 vs H.265 codec comparison for how to squeeze the file size down further without touching the container format at all.
Frequently Asked Questions
Which format should I use for YouTube uploads?
MP4 with H.264 video and AAC audio is YouTube’s recommended upload format, and it’s what nearly every camera, phone, and editing tool exports by default. WebM also works, but MP4 remains the safest, most universally tested choice.
Why are MOV files so much larger than MP4?
MOV files from iPhones or Mac editors often use Apple’s ProRes codec, designed to preserve maximum detail for editing rather than minimize file size. A standard H.264 MOV is roughly comparable in size to an equivalent MP4 — it’s specifically the high-quality editing codecs that inflate MOV file sizes.
Is WebM better than MP4?
It depends on context. WebM often achieves similar or slightly smaller file sizes at equivalent quality and is fully open and royalty-free. But MP4 is supported by more devices and apps outside the browser, which is why it remains the safer general-purpose choice.
Can all devices play AVI files?
No. Most smartphones can’t play AVI natively, and platforms like TikTok and Instagram reject AVI uploads entirely. AVI support today is mostly limited to older Windows software and dedicated media players like VLC — converting to MP4 is the reliable fix.