How to convert FLV to MKV
- Click Choose files or drop your FLV video into the box above.
- Keep the default quality, or choose a target size, resolution or frame rate.
- Click Convert and download the MKV when it is ready.
FLV vs MKV
| FLV | MKV | |
|---|---|---|
| Usual codecs | Sorenson Spark, VP6 or H.264 video with MP3 or AAC audio | Almost anything: H.264, HEVC, AV1, VP9 video; AAC, AC-3, DTS, Opus, FLAC audio; multiple subtitle and audio tracks |
| Plays on | Only VLC and similar players — Adobe Flash Player was discontinued in 2020 | VLC, Plex, Kodi and most PCs; not supported by iPhone, iPad, QuickTime, many video editors and most websites |
| Best for | Nothing today: convert old Flash videos to MP4 | Movies and TV episodes with several audio and subtitle tracks |
| Introduced | early 2000s by Macromedia / Adobe | 2002 by the Matroska open-source project |
About FLV and MKV
What is FLV?
FLV was the format behind early YouTube and most web video of the 2000s, played through Adobe Flash Player. Flash was shut down at the end of 2020, so FLV files no longer play in browsers. Converting them to MP4 keeps old videos watchable everywhere.
- Small files
- Obsolete: Flash Player is gone
- Plays only in a few desktop players
What is MKV?
MKV is a flexible open container that can hold almost any video and audio codec, several audio languages, subtitles and chapters in one file. That makes it popular for movies, but iPhones, QuickTime, iMovie, many editors and most websites do not accept MKV — converting to MP4 makes it play everywhere.
- Holds any codec
- Multiple audio and subtitle tracks, chapters
- Open and royalty-free
- Not supported on Apple devices, many TVs and editors
- Rejected by most upload sites
Why GlideConvert?
- Private by design. Your files are converted on your own device by your browser — they are never uploaded to a server. That keeps them private, avoids upload waits and means there is no queue.
- Fast. Images convert in a fraction of a second; video uses your device’s hardware encoder and is often simply repackaged without re-encoding.
- Free. No sign-up, no watermark. 10 images, 5 audio files or one video at a time — Pro lifts the limits and removes ads.
Frequently asked questions
Will converting FLV to MKV lose quality?
Often not at all. If the FLV file already contains video and audio that MKV supports (H.264 video and AAC audio are the most common), they are copied as-is: no quality loss, and even a large file converts in seconds. Otherwise the video is re-encoded at high quality — choose a quality level or a target file size in the options.
How long does converting FLV to MKV take?
Usually much less than the length of the video: modern browsers encode video with your device’s hardware. FLV needs a universal decoder (FFmpeg compiled to WebAssembly, a one-time ~32 MB download) which is slower — expect roughly real-time speed for HD video.
Is FLV still worth keeping?
FLV is obsolete — Flash Player was discontinued in 2020. Converting to MP4 keeps your videos watchable on any device for years to come.
Is there a file size limit?
On the free plan each video or audio file can be up to 500 MB and each image up to 100 MB. With Pro the limit is 4 GB per file. Because everything happens on your device, the practical limit for very large files is your device’s memory.
Are my files uploaded to a server?
No. GlideConvert runs entirely in your browser: images are processed with the browser’s built-in codecs and WebAssembly, video and audio with hardware-accelerated WebCodecs (or a WebAssembly build of FFmpeg for older formats). Nothing is sent anywhere — you can even disconnect from the internet once the page has loaded.
Does it work on iPhone, Android, Mac and Windows?
Yes. It works in any up-to-date browser — Chrome, Edge, Safari, Firefox or Samsung Internet — on phones, tablets and computers, with nothing to install. Long or 4K videos convert faster on a computer than on a phone.