Video Container vs Codec: Understanding MP4, WebM, AVI, and MKV
Demystify the relationship between video containers and codecs. Learn why changing a file extension does not convert video, and how to choose the right container-codec combination for your needs.
Key Takeaways
- A container (MP4, WebM, MKV) is a wrapper that holds encoded video, audio, subtitles, and metadata.
- For maximum browser compatibility, use MP4 with H.264 video and AAC audio.
- Re-encoding video is computationally intensive.
分辨率参考
常见屏幕分辨率参考
Containers and Codecs Are Different Things
A container (MP4, WebM, MKV) is a wrapper that holds encoded video, audio, subtitles, and metadata. A codec (H.264, VP9, AV1) is the algorithm that compresses and decompresses the actual video data. Renaming a file from .avi to .mp4 does not re-encode the video — it just changes the wrapper, often producing a broken file.
Container Comparison
| Container | Common Codecs | Streaming | Subtitles | Patent Status |
|---|---|---|---|---|
| MP4 (.mp4) | H.264, H.265, AAC | Yes | Limited | Patented codecs |
| WebM (.webm) | VP8, VP9, AV1, Opus | Yes | WebVTT | Royalty-free |
| MKV (.mkv) | Any codec | Limited | Extensive | Open format |
| AVI (.avi) | Legacy codecs | No | Limited | Legacy |
| MOV (.mov) | H.264, ProRes | Yes | Limited | Apple ecosystem |
Codec Comparison
| Codec | Compression | Speed | Quality | Browser Support |
|---|---|---|---|---|
| H.264 | Good | Fast encode/decode | Good | Universal |
| H.265 (HEVC) | 50% better than H.264 | Slow encode | Excellent | Safari, some others |
| VP9 | Similar to H.265 | Medium | Excellent | Chrome, Firefox, Edge |
| AV1 | 30% better than VP9 | Very slow encode | Best | Growing support |
Choosing for the Web
For maximum browser compatibility, use MP4 with H.264 video and AAC audio. For better compression, add a WebM (VP9/Opus) source and let browsers choose. AV1 offers the best quality per bit but encoding is computationally expensive.
Conversion Tips
Re-encoding video is computationally intensive. Use stream copying (-c copy in FFmpeg) when changing containers without changing codecs — it completes in seconds instead of minutes.