Convert FLV to MKV Online
Convert Flash FLV video to Matroska MKV container, losslessly.
.flv · up to 100 MB
What you can do
FLV to MKV: rescue the Flash archive
No quality loss
Pure remux: video bytes copied without re-encoding. Quality identical to the original.
Historical archive
Pre-2015 YouTube, Macromedia Flash, corporate recordings — all preserved in MKV.
Subtitles in MKV
Add SRT, SSA, or VobSub tracks with MKVToolNix after converting. Impossible in FLV.
100% private
Conversion runs in your browser with FFmpeg.wasm. Your video never leaves your device.
How it works
Three steps, no hassle
Upload your FLV file
Drag or select your .flv file. Pre-2015 YouTube downloads, Macromedia Flash recordings, or screen capture archives. No signup.
Remux to MKV
The video and audio stream transfer to the Matroska container. No re-encoding, no quality loss. Takes seconds.
Download your MKV
MKV file ready for Plex, Kodi, VLC, or any modern player. Supports added subtitle tracks.
FAQ
Got questions?
FLV (Flash Video) was created by Macromedia in 2002 and became the dominant internet video format from 2005 to 2015. YouTube used it as its primary delivery format until 2015 when it migrated to MP4/WebM. FLV uses Sorenson Spark (H.263) or VP6 for older files and H.264 for newer ones. Adobe Flash Player, required to play FLV, was officially discontinued on December 31, 2020. Converting FLV to MKV lets you access those historical files with any modern player.
No. FLV to MKV conversion is a container remux: the video stream bytes (Sorenson Spark, VP6, or H.264) are copied without decoding or re-encoding into the Matroska container. Video quality is mathematically identical to the original FLV.
MKV (Matroska) is a fully open container supporting multiple video, audio, and subtitle tracks. FLV has very limited subtitle support (only on2 text or screen markers) and no multiple audio tracks. MKV is the standard format for media libraries in Plex, Kodi, and Jellyfin, and will remain playable for decades.
Yes, that's one of MKV's main advantages over FLV. Once converted to MKV, you can use MKVToolNix to add SRT, SSA/ASS, VobSub, or PGS subtitle tracks as selectable streams. FLV only supports embedded text markers, not separate subtitle tracks.
Yes. FLV files downloaded from YouTube between 2005 and 2015 use H.264 (modern FLV) or VP6/Sorenson Spark (older ones). All these streams encapsulate correctly in Matroska. YouTube archives downloaded before 2010 typically use VP6 with MP3 audio — also remuxed without issues.
Yes. Many screen recording programs from 2005–2015 (Camtasia, Captivate, Adobe Connect) used FLV as output format. These can be remuxed to MKV correctly. FLV files with AAC or MP3 audio and H.264 video have full compatibility. Sorenson Spark or VP6 streams also work, though some modern players may need an additional codec to decode them.
Convert FLV to MKV: rescue Flash video in a modern container
FLV (Flash Video) dominated internet streaming for a complete decade. Macromedia introduced the format in 2002 as part of Flash MX, and adoption exploded when Adobe acquired Macromedia in December 2005 for $3.4 billion. YouTube, founded in February 2005, adopted FLV as its primary delivery format from its earliest months. Between 2006 and 2015, virtually all internet video was delivered via Flash Player inside FLV containers: concerts, documentaries, political debates, early recordings of now-famous artists. FLV files from YouTube used Sorenson Spark (H.263) or VP6 with MP3 audio for files before 2008, and H.264 with AAC for later files. YouTube began migrating to native HTML5 (MP4 and WebM) in 2014, completing the transition in January 2015. Adobe Flash Player was officially discontinued on December 31, 2020, and starting January 12, 2021 Adobe actively blocked Flash content execution. This history makes millions of FLV files historical documents requiring conversion to remain accessible.
Matroska MKV is the natural destination for historical FLV archives for several technical and practical reasons. Matroska, developed since 2002 by Steve Lhomme and Moritz Bunkus as a fully open alternative to AVI and MOV, can contain any combination of video streams (Sorenson Spark, VP6, H.264, H.265, AV1), audio (MP3, AAC, AC3, Opus), and subtitles (SRT, SSA/ASS, VobSub, PGS) as selectable tracks. FLV, by contrast, is a linear container with very limited subtitle support: it allows ScreenVideo text markers and onCuePoint data for embedded subtitles, but no separate selectable subtitle tracks at playback time. Plex Media Server, Kodi, Jellyfin, and practically all media library players use MKV as their preferred format for metadata management, thumbnails, and subtitles. Converting your historical FLV files to MKV not only preserves the video indefinitely but integrates it into your modern media ecosystem.
Convertir.ai executes the FLV to MKV conversion in your browser using FFmpeg.wasm. For FLV with H.264 and AAC, the operation is a pure remux: H.264 Annex B stream bytes (as stored in FLV) are converted to the AVCC format used in Matroska, and AAC audio is encapsulated directly. For FLV with VP6 or Sorenson Spark, the streams are also copied — though playback in Matroska depends on codec support in the target player: VLC includes support for both codecs, while Plex may need server-side transcoding. Processing a 500 MB FLV file typically takes under 30 seconds on a modern machine, with no quantity limits and no files leaving your device.