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?
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When the FLV and MKV containers can both carry the same codec (H.264, H.265, VP9, AV1), the converter falls back to a remux: the elementary streams are copied byte-for-byte into the MKV container and only the wrapper changes. A remux of a 1 GB FLV into MKV typically finishes in 5-15 seconds with zero quality loss. 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?
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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?
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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?
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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 if the source shipped with a chapter list it was in a sidecar file — hand that to the converter and it gets written into the MKV.
Is it worth converting old FLV recordings to MKV at all?
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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?
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Yes — every audio track in the FLV (director commentary, alternate languages, descriptive audio) is preserved in the MKV when the target container supports multi-stream audio. MKV and MOV handle unlimited audio tracks; MP4 supports many but some hardware players only see track 1; WebM is capped at one Opus / Vorbis track. 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?
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Soft subtitles (selectable tracks) survive when MKV can carry them: MKV holds SRT, ASS, SSA, PGS, VobSub natively; MP4 only holds mov_text (a stripped-down format). Converting an MKV with ASS styled subs to MP4 will typically downgrade them to mov_text or burn them in. Hardsubs (burned into the video) carry over regardless.
Does FLV to MKV keep chapter markers / DVD-style navigation?
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Chapter metadata transfers between FLV and MKV whenever both containers support a chapter atom (MKV, MP4, MOV). WebM stores chapters in a Matroska-compatible block, so MKV <-> WebM chapters round-trip cleanly. AVI has no chapter spec at all, so an AVI source arrives with no chapters to carry across and an AVI target cannot store the ones it was handed; add markers manually afterwards if you need them.
What about MKV attachments (fonts, cover art) when going FLV to MKV?
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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?
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The default codec is chosen to match the MKV container conservatively: MKV defaults to H.265 (HEVC) for better compression; MP4 defaults to H.264 for the widest device support; WebM defaults to VP9; AVI uses MPEG-4 ASP (DivX/Xvid lineage). Override via the advanced codec dropdown — AV1 is available for MKV / WebM where you want maximum compression and can wait through the encode. 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?
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HDR static metadata (HDR10 mastering display values, max content light level) carries through to MKV when both containers and the chosen codec support it (HEVC, AV1 in MKV / MP4). Dolby Vision is more fragile — DV profile 5 / 7 / 8.1 in FLV commonly survives only into MKV with HEVC; converting to an MKV container that does not carry the DV layer flattens to HDR10.
Will the FLV to MKV converter keep variable framerate (VFR)?
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MKV and WebM record real per-frame timestamps and handle VFR natively, so FLV VFR survives into an MKV of those formats with no resampling. MP4 nominally stores timestamps too but some players assume CFR; the converter exposes a "force CFR" toggle that resamples VFR FLV to 24 / 30 / 60 fps MKV for problematic targets.
FLV (Flash Video) is a video container format developed by Adobe. It is commonly used for online video streaming and is supported by Adobe Flash Player.
