Step 1: Provide your FLV files using the button above or by toss and let go.
Step 2: Click the 'Convert' button to start the conversion.
Step 3: Fetch your converted MKV files.
FLV to MKV Conversion FAQ
How do I convert FLV to MKV without re-encoding the video stream?
+
There is no stream-copy switch on this page. A few pairs copy a compatible video stream into the MKV container without re-encoding it, MKV to MP4 among them, which is quick and loses no quality. Most pairs re-encode the video. FLV typically holds Sorenson Spark or H.264 video with MP3 or AAC audio, wrapped in a stream format designed for RTMP delivery. MKV is codec-agnostic: H.264, HEVC, VP9 and AV1 video sit happily beside AAC, FLAC, Opus, DTS or Dolby audio in the same file.
Can I add selectable subtitles once the file is MKV?
+
Yes. FLV has no usable soft-subtitle track, so subtitles for FLV content had to be burned into the picture or shipped as a separate sidecar file. MKV carries subtitles as their own selectable stream, so after conversion you can attach an SRT track the viewer can switch on, switch off or restyle.
Can the MKV hold more than one audio track?
+
Yes, and it is a real upgrade over FLV. MKV treats every audio stream as a first-class track, so an original-language mix, a dub and a director commentary can live in one file with the player switching between them on demand. MKV is the archival container of choice because it stores unlimited audio tracks, soft subtitles, chapter markers and cover art in one file.
Does MKV support chapter markers that FLV did not?
+
It does. MKV stores chapters as container metadata, so a long recording can be navigated by section instead of by scrubbing a progress bar. FLV has nowhere to put that information, so the converted MKV starts with no chapters; add markers afterwards with a tool such as MKVToolNix or ffmpeg.
Is it worth converting old FLV recordings to MKV at all?
+
For anything you intend to keep, yes. FLV belongs to an earlier generation of video tooling and the software that reads it is steadily disappearing from phones, browsers and operating systems. Moving the footage to MKV now, while a clean decoder still exists, is the difference between an archive you can open in ten years and one you cannot. No current browser, phone or TV can play FLV — anything still in this container has to be moved out of it to remain watchable.
Will multi-track audio survive FLV to MKV conversion?
+
Usually not. Most conversions keep one audio track, the one with the most channels (normally the main mix), re-encoded for the MKV container, so commentary and alternate-language tracks are dropped. AVI, WMV, MPEG, FLV, VOB and M4V to MKV keep every track, and so does MP4 to MOV. To keep a different track, remux the FLV with that track first (VLC or ffmpeg can do this), then convert it. MKV is Matroska, an open container designed in 2002 with no licensing restrictions and no ceiling on what it can hold.
Are subtitle tracks preserved when converting FLV to MKV?
+
On some pairs. MP4 to MOV keeps every text subtitle track. AVI, WMV, MPEG, FLV, VOB and M4V to MKV keep every subtitle track: text subtitles are copied or converted to SRT, and picture-based subtitles such as DVD or Blu-ray ones are copied as they are. MP4, MOV and WebM to MKV keep only the first subtitle track (as ASS), and MP4 to WebM keeps the first one as WebVTT. Other pairs, including MKV to MP4 or MOV and WebM to MP4, drop subtitle tracks, and the converter does not burn them into the picture. Subtitles that are already burned in stay, because they are part of the video frames.
What about MKV attachments (fonts, cover art) when going FLV to MKV?
+
MKV is the only mainstream container that stores arbitrary attached files (TTF fonts for ASS subs, JPG cover art, fan-translated PDF inserts). Going from FLV to MKV drops these attachments when MKV is not MKV — the elementary streams convert, but the attached payload stays in the source. Keep FLV as a backup if you depend on attached fonts.
Which codec does the MKV output use by default?
+
It depends on the MKV container. MP4, MOV and MKV output use H.264, which plays on practically every phone, browser and TV. WebM output uses VP9. AVI, WMV and MPEG output use the older codecs those formats were designed for. MKV has almost no native hardware support — phones, browsers and TVs usually need VLC or a remux before they will play it.
How does HDR (HDR10, Dolby Vision) survive FLV to MKV?
+
There is no HDR processing or tone mapping. When the video stream is copied (MKV to MP4 or MOV with the default settings), HDR10 passes through as it is. When the video is re-encoded, the HDR10 mastering metadata is dropped and Dolby Vision or HDR10+ data is not kept, and with a Quality, Resolution or Frame Rate setting some pairs also reduce the video to 8-bit colour, so an HDR FLV can look washed out in the MKV.
