Convert FLV to MKV — Free Online Converter
Convert Flash Video (.flv) to Matroska Video (.mkv) online for free. Fast, secure video conversion with no watermarks or registration....
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Upload your .flv file by dragging it into the upload area or clicking to browse.
Choose your output settings. The default settings work great for most files.
Click Convert and download your .mkv file when it's ready.
About FLV to MKV Conversion
FLV (Flash Video) is Adobe's proprietary streaming container with limited metadata and subtitle support. MKV (Matroska Video) is an open-standard container released in 2002, designed to hold an unlimited number of video, audio, subtitle, and metadata tracks in a single file. Named after Russian Matryoshka dolls, MKV supports virtually every codec ever created — H.264, H.265, VP9, AV1, FLAC, DTS, and hundreds more. Converting FLV to MKV preserves all content while upgrading to a far more capable container.
Why Convert FLV to MKV?
MKV is the preferred container for media archivists and power users because it supports every codec without the licensing restrictions of MP4. You can attach multiple audio tracks (different languages), multiple subtitle streams (SRT, SSA/ASS, PGS), chapter markers, fonts, and even attachments. MKV files play natively on VLC, mpv, Kodi, Plex, and most smart TVs, making it the most flexible container available.
Common Use Cases
- Archiving FLV video collections in a modern container that preserves all streams and metadata
- Remuxing FLV files with added subtitles and alternate audio tracks into a single MKV package
- Creating a Plex or Kodi media library from archived FLV downloads with full metadata support
- Preserving FLV content in an open-standard format immune to vendor-specific format obsolescence
- Migrating FLV recordings to MKV for compatibility with modern hardware media players like Roku and Shield TV
How It Works
When the FLV contains H.264 video and AAC audio, FFmpeg can remux directly to MKV without re-encoding — the codec streams are copied verbatim into the Matroska container. For FLV files with Sorenson Spark or VP6, re-encoding to H.264 or H.265 is performed. MKV's EBML (Extensible Binary Meta Language) structure supports per-stream language tags, chapter markers with named chapters, and embedded fonts for styled subtitles.
Quality & Performance
When remuxing (stream copy), quality is completely preserved — the operation is lossless and near-instantaneous. When re-encoding from older FLV codecs, H.264 or H.265 in MKV provides equivalent or better visual quality at similar bitrates. MKV itself introduces zero overhead — it is purely a container and does not affect codec-level quality.
Device Compatibility
| Device | FLV | MKV |
|---|---|---|
| Windows PC | Partial | Partial |
| macOS | Partial | Partial |
| iPhone/iPad | Partial | Partial |
| Android | Partial | Partial |
| Linux | Partial | Partial |
| Web Browser | No | No |
Recommended Settings by Platform
YouTube
Resolution: 1920x1080
Bitrate: 8-12 Mbps
H.264 recommended for fast processing
Resolution: 1080x1080
Bitrate: 3.5 Mbps
Square or 9:16 for Reels
TikTok
Resolution: 1080x1920
Bitrate: 4 Mbps
9:16 vertical, under 60s ideal
Twitter/X
Resolution: 1280x720
Bitrate: 5 Mbps
Under 140s, 512MB max
Resolution: 960x540
Bitrate: 2 Mbps
16MB limit for standard, 64MB for document
Discord
Resolution: 1280x720
Bitrate: 4 Mbps
8MB free, 50MB Nitro
Tips for Best Results
- 1Use remux mode (stream copy) whenever the FLV contains H.264 — this preserves quality perfectly and converts in seconds
- 2Add a chapter file if the FLV contains distinct segments (lectures, episodes) — MKV chapters enable quick navigation in players like VLC
- 3Set the MKV default audio track language tag for proper automatic track selection in media players
- 4Embed subtitles as a separate track (not burned in) so viewers can toggle them on and off
- 5Use MKV for archival and transcode to MP4 only when you need to share with Apple devices or upload to social media
Related Conversions
FLV to MKV conversion upgrades obsolete Flash content to the most capable open multimedia container available. Whether remuxing for archival or re-encoding for broader compatibility, MKV provides unmatched flexibility for multi-track, multi-subtitle media.