Convert FLV to MKV Online Free

Convert Flash Video FLV files to Matroska MKV format for modern media player compatibility and efficient long-term video archiving. ChangeThisFile handles conversion with FFmpeg on secure servers.

By ChangeThisFile Team · Last updated: March 2026

Quick Answer

ChangeThisFile converts FLV to Matroska using FFmpeg, a professional-grade multimedia framework, to transcode FLV files to Matroska format with optimized codec settings and quality preservation. Free with no signup required. Files are encrypted during transfer and automatically deleted from our servers after conversion.

Free No signup required Encrypted transfer · Auto-deleted Under 2 minutes Updated March 2026

Convert FLV to Matroska

Drop your FLV file here to convert it instantly

Drag & drop your .flv file here, or click to browse

Convert to Matroska instantly

FLV vs Matroska: Format Comparison

Key differences between the two formats

Feature	FLV	MKV (Matroska)
Full Name	Flash Video	Matroska Video
Developer	Adobe Systems	Matroska.org
Status	Deprecated	Actively maintained
Video Codec	H.263, VP6, H.264	H.264, H.265, VP9, AV1
Audio Codec	MP3, AAC, Nellymoser	AAC, FLAC, AC-3, Opus
Subtitle Support	None	SRT, ASS, PGS and more
Multiple Tracks	No	Yes (video, audio, subtitles)
Modern Media Players	VLC only	VLC, MPC-HC, Kodi, and more

When to Convert

Common scenarios where this conversion is useful

Flash Archive Migration

Convert legacy FLV video archives to the modern, open Matroska format for long-term preservation and broader media player compatibility.

Kodi and HTPC Media Libraries

Add FLV content to Kodi or other HTPC media center libraries by converting to MKV, which is universally supported by home theater software.

Adding Subtitle Tracks

Convert FLV to MKV to then mux in subtitle tracks (SRT, ASS), taking advantage of Matroska's superior subtitle support.

VLC and Media Player Organization

Organize a large FLV video library in the more modern and widely-recognized MKV format for easier management and playback.

Re-encoding for Better Compression

Convert FLV files to MKV with modern H.265 encoding for significant file size reduction while maintaining or improving quality.

Who Uses This Conversion

Tailored guidance for different workflows

Content Creators

Convert FLV footage to Matroska for uploading to YouTube, TikTok, or social media platforms
Transform FLV screen recordings to Matroska for sharing in blog posts or tutorials

Choose Matroska at 1080p or higher for the best quality-to-size ratio on social platforms

Preview the converted Matroska file before uploading to ensure audio sync is maintained

Video Editors

Convert FLV raw footage to Matroska for importing into editing software like Premiere or DaVinci Resolve
Transform FLV project exports to Matroska for client delivery or final distribution

Maintain the original resolution and frame rate during FLV to Matroska conversion to avoid quality loss

Use a high bitrate when converting to Matroska if the footage will undergo further editing

Social Media Managers

Convert FLV brand videos to Matroska to meet platform-specific format requirements
Transform FLV ad creatives to Matroska for cross-platform publishing campaigns

Check each platform's recommended Matroska specs (resolution, bitrate, duration) before uploading

Keep the FLV original archived for future re-exports at different resolutions

How to Convert FLV to Matroska

1

Upload Your FLV File

Select or drag your Flash Video FLV into the upload area. Your file is transmitted securely using HTTPS encryption.
2

Server-Side Conversion to MKV

FFmpeg remuxes or transcodes your FLV into the Matroska MKV container, preserving H.264 video and re-encoding audio to AAC for modern compatibility.
3

Download Your MKV File

Your converted Matroska MKV downloads when ready. The original FLV is permanently deleted from our servers immediately after.

Frequently Asked Questions

Why convert FLV to MKV?

MKV is a modern, open container format widely supported by VLC, Kodi, and all major media players. Converting FLV to MKV makes legacy Flash Video accessible on modern systems without Flash Player.

Can I add subtitles to the MKV after conversion?

Yes. MKV's strong subtitle support means you can mux in SRT, ASS, or other subtitle formats using tools like MKVToolNix after converting from FLV.

Will FFmpeg lose quality during conversion?

If the FLV uses H.264, FFmpeg can often remux with minimal quality change. If transcoding is required (H.263, VP6 sources), some quality loss may occur.

What FLV audio codecs are supported?

FFmpeg supports MP3, AAC, and Nellymoser audio found in FLV files. All are converted to AAC in the MKV output for maximum compatibility.

Does MKV have a size advantage over FLV?

MKV and FLV at the same codec and bitrate will have similar file sizes. The advantage of MKV is codec flexibility — you can use modern codecs like H.265 for better compression.

Is there a file size limit?

Up to 25MB per file (free tier; 500MB on Pro). Trim larger FLV archives before uploading to ChangeThisFile.

Is my FLV file private?

Yes. Files are encrypted during upload and deleted immediately after conversion. No content is retained or analyzed.

What media players support MKV?

VLC, MPC-HC, Kodi, PotPlayer, mpv, Windows 11's native player, and most modern media players support MKV natively.

How long does conversion take?

Most FLV to MKV conversions complete within a minute. Processing time depends on file size and resolution.

Is this free?

Yes. ChangeThisFile is free with no accounts, subscriptions, or watermarks.

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Need to convert programmatically?

Use the ChangeThisFile API to convert FLV to Matroska in your app. No rate limits, up to 500MB files, simple REST endpoint.

View API Docs

Read our guides on file formats and conversion

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