## What Is MKV?
**MKV** (Matroska Video) is an open-source multimedia container format developed since 2002. Not a codec — a "wrapper" that holds virtually any combination of video, audio, subtitles, and chapters.
## What Can an MKV Contain?
| Element | Details |
|---------|---------|
| **Video tracks** | H.264, H.265, VP9, AV1, etc. |
| **Audio tracks** | AAC, AC3/Dolby, DTS, FLAC, MP3, Opus |
| **Subtitles** | SRT, ASS/SSA, PGS, VobSub — selectable |
| **Chapters** | Named markers |
| **Metadata** | Title, date, tags |
## MKV vs MP4 vs AVI
| Feature | MKV | MP4 | AVI |
|---------|-----|-----|-----|
| Multiple audio tracks | ✅ | ✅ | Limited |
| Embedded subtitles | ✅ (many formats) | ✅ (limited) | ❌ |
| Chapters | ✅ | ✅ | ❌ |
| HTTP streaming | Limited | ✅ | ❌ |
| Apple native support | ❌ | ✅ | ❌ |
| Corruption recovery | ✅ | Partial | ❌ |
## Basic FFmpeg Operations
### Remux MKV to MP4 (no re-encoding)
```bash
ffmpeg -i video.mkv -c copy video.mp4
# Force AAC if audio is DTS/AC3
ffmpeg -i video.mkv -c:v copy -c:a aac -b:a 192k video.mp4
```
### Extract Subtitles
```bash
ffprobe -v error -show_entries stream=index,codec_type,codec_name -of csv video.mkv
ffmpeg -i video.mkv -map 0:s:0 subtitles.srt
ffmpeg -i video.mkv -map 0:s:0 subtitles.ass
```
### Add Subtitles
```bash
ffmpeg -i video.mkv -i subtitles.srt \
-c copy -metadata:s:s:0 language=eng video_with_subs.mkv
ffmpeg -i video.mkv -i subs_en.srt -i subs_es.srt \
-c copy \
-metadata:s:s:0 language=eng \
-metadata:s:s:1 language=spa \
video_multilang.mkv
```
### Extract Audio Tracks
```bash
ffmpeg -i video.mkv -map 0:a:0 -c:a flac audio.flac
ffmpeg -i video.mkv -map 0:a:1 -c:a aac audio_2.aac
```
## Compatible Players
| Player | MKV Support |
|--------|------------|
| **VLC** | ✅ Full |
| **MPV** | ✅ Full |
| **Kodi** | ✅ Full |
| **Windows Media Player** | ❌ |
| **QuickTime** | ❌ |
## When to Use MKV
**Use MKV for:** local files with multiple languages/subtitles, lossless Blu-ray quality preservation.
**Use MP4 for:** web streaming, Apple devices, sharing with non-technical users.
## Conclusion
**MKV is the most flexible video container** for high-quality content with multiple tracks. For universal distribution, remux to MP4 without re-encoding with `-c copy`.
Guide