How to Convert MKV and AVI to MP4 Free Online (2026)

Why Won't My Video Play?

If you've downloaded a video in MKV or AVI format and it won't play on your phone, TV, or in a browser — the problem is the format. MP4 is the universal video standard that works everywhere.

MKV vs AVI vs MP4

| Feature | MKV | AVI | MP4 | |---------|-----|-----|-----| | Quality | Excellent | Good | Excellent | | File size | Large | Very large | Compact | | Device support | Limited | Limited | Universal | | Subtitles | Built-in | External only | Built-in | | Web streaming | No | No | Yes | | Social media | No | No | Yes |

When to Convert MKV to MP4

• Phone playback: Most phones play MP4 natively
• Smart TVs: Many TVs don't support MKV
• Social media: Instagram, TikTok, Twitter all require MP4
• Web embedding: Browsers support MP4, not MKV
• Sharing: Smaller files, universal compatibility

When to Convert AVI to MP4

• File size: AVI files are often 2-3x larger than MP4
• Modern devices: AVI is a 1990s format, many new devices dropped support
• Streaming: AVI doesn't support web streaming
• Quality: MP4 with H.264 offers better compression with same quality

How to Convert

MKV to MP4

1. Open our MKV to MP4 converter
2. Upload your MKV file
3. Choose resolution and quality settings
4. Click Convert and download

AVI to MP4

1. Open our AVI to MP4 converter
2. Upload your AVI file
3. Adjust settings if needed
4. Click Convert and download

Tips for Best Results

1. Keep original resolution: Don't upscale — it doesn't improve quality
2. Use default settings: Our presets are optimized for quality and speed
3. Large files: Videos over 50MB may take longer to process
4. Subtitles: MKV subtitles are preserved when possible

Bonus: GIF Conversions

Want to create a GIF from your video or convert a GIF to MP4?

• GIF to MP4 — smaller files, better quality
• MP4 to GIF — create animated GIFs from any video

Conclusion

MP4 is the universal video format. Converting MKV or AVI to MP4 ensures your videos work on any device, anywhere.