CONVERT MKV → FLV (MKV to FLV)
Fast, secure MKV to FLV conversion. No registration required.
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HOW TO CONVERT MKV → FLV
Drop the video file
Select a MKV file. We read the container and stream descriptors to plan the conversion.
FFmpeg handles the repackage
When codecs align, FFmpeg rewraps the existing streams into a FLV container — no quality loss, near-instant finish.
Retrieve the FLV
The FLV download is ready in seconds for stream-copy jobs, minutes for full transcodes.
Starting point: MKV is the Matroska container, flexible enough to carry nearly any codec plus chapters and subtitles. Natural next step, a FLV. A MKV to FLV conversion makes a recording portable. Video containers matter more than you might expect: players that handle FLV natively sometimes stutter or flat-out reject MKV with the same codec inside. Uploading above triggers a stream-level rewrap when possible, keeping the visible quality identical to the source. A quick refresher — MKV is the Matroska container, flexible enough to carry nearly any codec plus chapters and subtitles. By contrast, FLV is the Adobe Flash Video container, now deprecated but still lingering in archives.
Why convert MKV to FLV
Sending MKV to someone on a non-matching operating system frequently leads to "file cannot be opened". FLV avoids that by sitting in the middle of everyone's compatibility list. The repackage runs quickly and without generational loss when codecs already align.
MKV vs FLV — Technical specifications
Side-by-side comparison of the technical details.
MKV
- MIME type
- video/x-matroska
- Extensions
- .mkv, .mka (audio), .mks (subtitles)
- Container structure
- EBML (Extensible Binary Meta Language)
- Related
- WebM (restricted MKV subset)
- Max tracks
- Practically unlimited
- MIME Type
- video/x-matroska
- Extension
- .mkv
- Category
- Video Files
- Full Name
- Matroska Video
- Conversion Engine
- FFMPEG
FLV
- MIME type
- video/x-flv
- Extensions
- .flv, .f4v
- MIME Type
- video/x-flv
- Extension
- .flv
- Category
- Video Files
- Full Name
- Flash Video
- Conversion Engine
- FFMPEG
- Video codecs
- Sorenson Spark, VP6, H.264 (F4V)
- Audio codecs
- MP3, Nellymoser, AAC
- Status
- Deprecated since December 31, 2020
| Specification | MKV | FLV |
|---|---|---|
| MIME type | video/x-matroska | video/x-flv |
| Extensions | .mkv, .mka (audio), .mks (subtitles) | .flv, .f4v |
| Container structure | EBML (Extensible Binary Meta Language) | — |
| Related | WebM (restricted MKV subset) | — |
| Max tracks | Practically unlimited | — |
| MIME Type | video/x-matroska | video/x-flv |
| Extension | .mkv | .flv |
| Category | Video Files | Video Files |
| Full Name | Matroska Video | Flash Video |
| Conversion Engine | FFMPEG | FFMPEG |
| Video codecs | — | Sorenson Spark, VP6, H.264 (F4V) |
| Audio codecs | — | MP3, Nellymoser, AAC |
| Status | — | Deprecated since December 31, 2020 |
MKV vs FLV — Strengths and limitations
What each format does best, and where it falls short.
MKV Strengths
- Carries virtually any codec — H.264, H.265, AV1, VP9, Opus, FLAC, AAC, you name it.
- Multiple audio and subtitle tracks, chapters, and menus in one file.
- Patent-free container — no licensing fees.
- Attached fonts and metadata ride along for self-contained playback.
- Streamable and seekable with built-in index/cue tables.
Limitations
- Not natively supported in Apple's QuickTime or Safari without third-party tools.
- Windows needed codec packs (or "Films & TV" app updates) to play it out of the box.
- Hardware decoders on older TVs and streamers often reject MKV.
FLV Strengths
- Low overhead — the container is extremely compact.
- Designed for streaming — progressive download and seeking work well.
- Decoded natively by Flash Player on every OS for 20 years.
Limitations
- Flash Player is dead — no modern browser can play FLV without conversion.
- Legacy codecs (Sorenson, VP6) are poorly supported in modern tooling.
- Hardware video decoders never added FLV support.
Quality & Compatibility
Resolution, frame rate and colour space are preserved end-to-end. If the FLV container does not support some MKV features (chapters, multiple subtitle tracks, DRM-protected streams), those are flattened or dropped with a warning. Hard-coded subtitles in the video frames always survive.
Tips for Best Results
- Embedded subtitle tracks convert between MKV and FLV when both containers support the same subtitle codec; otherwise burn the subtitles into the video first.
- For portrait (9:16) clips, make sure the FLV encoder preserves the correct display aspect ratio — some players default to 16:9 if SAR is ambiguous.
- Long recordings (over an hour) benefit from chapter metadata; FLV may not preserve MKV chapters — check before relying on them.
Frequently Asked Questions
Only when it has to. If the codecs inside MKV (usually H.264 or H.265 for video, AAC for audio) are accepted by FLV, we stream-copy — the bytes are repackaged into the new container with zero re-encoding and no quality loss. When the source uses a codec the target does not support, we transcode at a matching bitrate to keep the visual quality close to the original.
With stream copy, expect the job to finish in seconds to tens of seconds regardless of video length — the work is mostly rewriting the container. Transcoding is slower (roughly real-time: a ten-minute clip takes about ten minutes) because every frame must be decoded and re-encoded. The progress bar shows which mode applies.
Yes. Resolution, frame rate, colour space and bit depth are preserved by default; stream copy is literally bit-identical on these parameters. If you explicitly pick a lower bitrate or a different codec in Advanced, the output is rebuilt to those settings, but the default is always "match the source".
Matroska Video
Source formatMKV is a flexible, open-standard container format that can hold unlimited video, audio, subtitle, and metadata tracks. It is popular for high-definition video and supports virtually any codec.
Flash Video
Target formatFLV was the dominant web video format during the Flash era. While Flash is now deprecated, many legacy video files still exist in FLV format and need conversion to modern formats.
Going the other way? Convert FLV back to MKV with the same engine.
Common Use Cases
Share across platforms
Send FLV files to anyone without worrying about whether they have the right software for MKV.
Embed in documents
Drop FLV output into Word, Google Docs, PowerPoint, Notion or a website without conversion warnings.
Optimize size
FLV often produces smaller files than MKV for web, email and storage.
Archive & future-proof
Store in a widely-supported format that will still open on future operating systems without legacy plugins.
MKV vs FLV — Typical file sizes
Approximate file sizes for common scenarios.
- 45-min episode (H.264 1080p) 800 MB - 1.6 GB
- 2-hour movie (H.265 1080p) 1.5-3 GB
- 2-hour movie (4K HDR H.265) 15-40 GB
- 10-min YouTube 2008-era video 40-80 MB
- 45-min TV show (FLV H.264) 200-500 MB
Working with 4K/8K Video or Files Over 100MB?
Web browsers impose strict RAM limits on media streams. For gigabyte 4K/8K footage, GPU-accelerated NVENC transcode, or batch subtitle muxing, dedicated desktop encoders deliver zero upload delays.
One-time payment with zero recurring commitment: convert files up to 1 GB, OCR, PDF/A, and .ZIP batches for 24 hours.
Full 7 days of unlimited conversions, up to 2 GB per file, 100% ad-free with zero subscription.
High-throughput enterprise pipeline for files up to 2,048 MB, 50-file batches, ISO PDF/A, and priority processing.
Uncapped 4K/8K multi-track transcoding with hardware NVENC, VideoToolbox, and AV1/HEVC pipelines.
10-bit color grading workflows, Apple ProRes mastering, and automated watch-folder queues.
Related comparisons
See these formats side by side to understand which fits your use case best.
Related Guides
MKV/Matroska Container Format: The Open-Source Multimedia Powerhouse
Complete guide to MKV/Matroska container format: EBML architecture, unlimited codec support, chapter systems, PGS/ASS subtitles, mkvtoolnix commands, and...
Read guide →MKV (Matroska) Video Container: Complete Format Guide
Everything about MKV video containers — how Matroska works, supported codecs, subtitle tracks, chapters, and how to convert MKV files.
Read guide →FLV Files: Flash Video Format History, Codecs, and Conversion Guide
Complete guide to FLV (Flash Video) files — Sorenson/VP6/H.264 codecs, file structure, YouTube history, FFmpeg conversion to MP4/WebM, batch processing, and...
Read guide →
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