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FLV to MKV Converter

Convert FLV to MKV online for free. Fast, secure, and high-quality conversion with no sign-up or software required.

  • Free to use
  • No file stored beyond 1 hour
  • Encrypted over TLS 1.2/1.3
  • No watermarks

Drag and drop your files here or click to upload.

Maximum file size is 1GB

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How it works

Three steps to your converted file

Everything happens in your browser tab - upload, pick a format, download. The heavy lifting runs on our servers.

  1. 01

    Upload your file

    Drag and drop, click to browse, or paste a URL. Batches take up to 20 files at once - 230+ input formats across video, audio, image, document, and archive types.

  2. 02

    Choose an output format

    Pick from over a hundred output formats. Filter by category or search by name - every option is open to everyone, no account needed.

  3. 03

    Convert & download

    Hit Convert and grab your download link moments later. Originals are erased when the job completes; results are cleared within about an hour.

FLV to MKV

Why convert FLV to MKV?

FLV and MKV are both lossy formats.

  • Where MKV works best

    Movies with several audio tracks and subtitles.

FLV vs MKV: what's the difference?

PropertyFLVMKV
TypeVideoVideo
CompressionLossy (smaller files, some quality loss)Lossy (smaller files, some quality loss)
Opens inVLC; browsers dropped Flash in 2020VLC and most desktop players; few phones, TVs or browsers
Best forOld Flash web videosMovies with several audio tracks and subtitles

What is an FLV file?

Flash Video

Developed By
Adobe Systems
Initial Release
2002
MIME Type
video/x-flv

The FLV (Flash Video) format is a container file format defined by Adobe Systems for delivering synchronized audio and video over the internet via the Adobe Flash Player. It supports various codecs, historically Sorenson Spark and VP6, and later H.264 (MPEG-4 AVC) and AAC audio. FLV files were the dominant standard for web-based streaming video (YouTube, Hulu) during the 2000s, utilizing the RTMP (Real-Time Messaging Protocol) for transmission before being superseded by HTML5 standards.

How to open an FLV file

Since the End-of-Life (EOL) of Adobe Flash Player in 2020, browsers no longer support FLV natively. To play local FLV files, users must utilize third-party media players that maintain legacy codec support, such as VLC Media Player, MPC-HC, or MPV. For editing or conversion, tools like OBS Studio and HandBrake utilize the FFmpeg library to decode and process the container.

What is an MKV file?

Matroska Video Container

Developed By
Matroska (non-profit)
Initial Release
2002
MIME Type
video/x-matroska

The Matroska Video (MKV) file is an open-standard, free container format capable of holding an unlimited number of video, audio, picture, or subtitle tracks in one file. Unlike proprietary containers, Matroska is structured upon Extensible Binary Meta Language (EBML), allowing for significant flexibility and forward compatibility. It supports a vast array of codecs, including H.264, VP9, HEVC, AAC, Vorbis, and FLAC, and is particularly noted for its support of soft subtitles (SSA/ASS) and chapter entries, making it a standard for high-definition video distribution (HD) and anime fansubs.

How to open an MKV file

Native support for MKV is available in Windows 10/11 via the Movies & TV app and generally on Linux distributions. macOS requires third-party software, as QuickTime Player does not natively parse the Matroska container. The industry-standard solution for all operating systems is VLC Media Player, which includes built-in libraries for decoding the diverse codecs often encapsulated within MKV files. Alternative options include MPV and MPC-HC (Windows).

More tools

More free video tools

All video conversions

Why RunConvert

The fastest way to convert any file

Purpose-built for speed, privacy, and breadth of format support.

  • Convert FLV to MKV in seconds

    Every FLV to MKV conversion runs on our servers, so your device stays fast and the output quality stays intact.

  • Fast, cloud-powered

    No queue, no waiting. Files are processed on high-performance servers and returned in seconds, even for large files.

  • Secure & private

    Encrypted in transit and never shared with anyone. Uploads are erased the moment your job completes, and results shortly after.

  • Free - no account needed

    Convert without creating an account - no credit card, no trial clock. Sign in only if you want history and higher daily limits.

Developer API

Convert FLV to MKV via API

Automate FLV to MKV conversions in three steps: create a job, upload your file, then poll for the result.

Replace YOUR_API_KEY with your RunConvert API key. Get your free API key at runconvert.com/api.

# 1. Create job
curl -X POST https://api.runconvert.com/v3/jobs \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "tag": "flv-to-mkv",
    "tasks": {
      "upload-file": {
        "operation": "import/upload"
      },
      "convert": {
        "operation": "convert",
        "input": "upload-file",
        "output_format": "mkv"
      },
      "export-result": {
        "operation": "export/url",
        "input": "convert"
      }
    }
  }'

# 2. Upload your file (use upload_url from the response)
curl -X PUT "$UPLOAD_URL" --upload-file input.flv

# 3. Poll for result
curl https://api.runconvert.com/v3/jobs/$JOB_ID?include=tasks \
  -H "Authorization: Bearer YOUR_API_KEY"

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