You have an MKV that won't play on your TV, a MOV from your iPhone that Windows won't open, or a WMV from 2008 that nothing modern recognizes. Video formats are confusing because there are two layers: the container (what the file is called) and the codec (what's inside it).
Understanding that distinction makes every format decision straightforward.
Container vs Codec: The Core Distinction
Think of a container as a box, and the codec as the contents inside. MP4, MKV, MOV, and AVI are all boxes. H.264, H.265, VP9, and AV1 are all types of video data that can go inside those boxes.
The same H.264 video can be stored in an MP4 box, an MKV box, or a MOV box. The video quality is identical — only the box changes. But which box you use determines which devices can open it. An iPhone can open the MP4 box but not the MKV box, even though the video inside is the same.
This is why "converting" from MKV to MP4 sometimes takes seconds (it just moves the data from one box to another without touching it) and sometimes takes minutes (if it needs to re-encode the video because the codec isn't compatible with the new container).
MP4 — The Universal Standard
MP4 (MPEG-4 Part 14) is the most widely supported video format. Every device that plays video supports MP4: iPhones, Android phones, Smart TVs, gaming consoles, Windows, Mac, all web browsers, and every major streaming platform.
- Typical video codec: H.264 or H.265
- Typical audio codec: AAC
- File size: Medium — H.264 at good quality is larger than H.265
- Best for: Sharing with anyone, uploading to platforms, playback on mobile and TV When in doubt, use MP4. It's the correct default for almost every situation where you need other people to be able to open the file.
MKV — The Flexible Archive Format
MKV (Matroska) is the most capable container format. It supports an unlimited number of audio tracks, subtitle tracks, chapters, and virtually any video codec. It's popular for storing movie files with multiple language audio and subtitle options.
- Typical video codec: H.264, H.265, or VP9
- Typical audio codec: AAC, AC3, DTS, or FLAC (lossless)
- File size: Same as the codec used — the container adds negligible overhead
- Best for: Personal archive, files with multiple language tracks, use with VLC The downside: most mobile devices and consumer electronics don't support MKV natively. If you need to play an MKV on iPhone, PS5, or a Smart TV, convert it to MP4 first. See our guide on converting MKV to MP4 .
MOV — Apple's Native Format
MOV is Apple's QuickTime container format. iPhone cameras record in MOV (or HEVC/MOV). It's the native format for iMovie and Final Cut Pro. MOV plays natively on Mac and iOS, and reasonably well on Windows with QuickTime installed.
- Typical video codec: H.264, H.265, or ProRes (lossless, for professional editing)
- Typical audio codec: AAC or PCM (lossless)
- File size: Large with ProRes; similar to MP4 with H.264/H.265
- Best for: Apple workflows, professional video editing, iPhone exports For most sharing purposes, MOV and MP4 are interchangeable — they often contain the same codec. If you need to share a MOV with Windows users, converting to MP4 ensures maximum compatibility.
AVI and WMV — Legacy Formats
AVI (Audio Video Interleave) was Microsoft's dominant video format in the 1990s and early 2000s. WMV (Windows Media Video) followed. Both are now legacy formats with significant limitations:
- Poor support on mobile devices and modern TVs
- No native web browser support
- Limited subtitle support
- Often use older codecs (DivX, Xvid, WMV3) with lower quality at the same file size If you have old AVI or WMV files, convert them to MP4 for playback on modern devices. The video quality will be similar or better since modern codecs are more efficient than the legacy ones typically used in these files.
WebM — Open Web Format
WebM is an open-source container format developed by Google, designed for efficient web video streaming. It pairs with VP8, VP9, or AV1 video codecs and Opus audio — all royalty-free.
- Typical video codec: VP9 or AV1
- Typical audio codec: Opus
- Best for: Web video embedding, HTML5 video elements, open-source workflows
- Limitation: Safari/iOS support is limited; not suitable for MP4-only players
Video Codecs Compared
The codec inside the container has the biggest impact on file size and quality.
| Codec | Efficiency | Device support | Best for |
|---|---|---|---|
| H.264 (AVC) | Good | Universal | General use, sharing, streaming |
| H.265 (HEVC) | ~2× H.264 | Modern devices | 4K, storage-sensitive, newer devices |
| VP9 | Similar to H.265 | Chrome/Firefox, Android | Web video, YouTube |
| AV1 | ~30% better than H.265 | Growing rapidly | Streaming delivery, future storage |
| ProRes / DNxHD | Low (large files) | Professional apps only | Video editing, color grading |
Which Format to Choose
Sharing with others or playing on mobile/TV → MP4 (H.264) Works everywhere. Use H.265 if your recipient's device is modern.
Personal archive with multiple languages or subtitles → MKV Keep all tracks intact. Use VLC for playback.
Apple workflow, iMovie, Final Cut Pro → MOV Native Apple format. Convert to MP4 before sharing with non-Apple users.
Web video embed (not Safari required) → WebM Open, royalty-free, efficient. Pair with MP4 fallback for Safari.
Have AVI/WMV files → Convert to MP4 Legacy formats with poor modern compatibility. Convert and keep the MP4.
Our MKV to MP4 converter handles the most common conversion need. For other formats, check our full video conversion tools.