What is the difference between FLV and MKV?

FLV (Flash Video) is Adobe's proprietary container designed for the Flash Player plugin, which all major browsers have removed. MKV (Matroska Video) is an open-standard container that supports virtually any codec — H.264, H.265, AV1, VP9 — plus multiple audio tracks, embedded subtitles, and chapters. FLV is effectively dead for modern use; MKV is widely used for archiving and local media servers.

Will converting FLV to MKV reduce quality?

If your FLV already contains H.264 video and AAC or MP3 audio, FFmpeg can rewrap it to MKV using -c copy with zero quality loss — this is just a container change, no re-encoding. For FLV files with Sorenson Spark or On2 VP6 video, full re-encoding to H.264 or H.265 is required, which introduces some compression loss. Keep the CRF low (e.g., -crf 18) to minimize visible degradation.

Why choose MKV instead of MP4 when converting from FLV?

MKV is preferred when you need to preserve multiple audio tracks, embedded subtitle streams, or chapters — MP4 supports these but with more limitations. MKV also has no patent or licensing restrictions. For web upload or mobile playback, MP4 is better supported. For local archiving and media servers like Plex or Jellyfin, MKV is the standard choice.

Can I convert FLV to MKV without losing audio?

Yes. FFmpeg copies audio streams by default with -c copy if they are in a codec MKV supports (most are). If audio is missing in the output, force AAC: ffmpeg -i input.flv -c:v libx264 -crf 22 -c:a aac -b:a 192k output.mkv. Some FLV files use ADPCM or Nellymoser audio that requires re-encoding — FFmpeg handles both.

Is my video file uploaded anywhere?

No. The file inspector uses the browser's File API and URL.createObjectURL(). Your video file never leaves your device — there is no upload, no server processing, and no tracking of any kind.

How do I batch-convert many FLV files to MKV?

Use a bash loop with FFmpeg: for f in *.flv; do ffmpeg -i "$f" -c copy "${f%.flv}.mkv"; done. On Windows PowerShell: Get-ChildItem *.flv | ForEach-Object { ffmpeg -i $_.FullName -c copy ($_.BaseName + ".mkv") }. This rewraps all FLV files to MKV instantly if they contain H.264 + AAC.

What codecs does FLV typically contain?

FLV files typically hold Sorenson Spark (H.263) or On2 VP6 video with MP3 or ADPCM audio. Newer FLV files sometimes contain H.264 video and AAC audio (historically called F4V). Check your FLV codec first with: ffprobe -v quiet -show_streams input.flv. H.264 + AAC FLV can be rewrapped losslessly; others require re-encoding.

Can HandBrake output MKV directly?

Yes. HandBrake natively supports MKV as an output container. In the Summary tab, set Format to MKV and proceed with encoding. HandBrake also supports adding subtitle tracks to MKV, which makes it useful when you have external SRT files for the original FLV recording.

FLV to MKV Converter

Name: FLV to MKV Converter
Availability: InStock
Author: Nham Vu

Step-by-step guide for converting FLV video files to MKV format using FFmpeg, HandBrake, and VLC, plus a client-side FLV file metadata inspector.

Video File Inspector

Select any video file to read its metadata instantly — 100% client-side, nothing uploaded.

Click to choose a video file FLV, MKV, AVI, MOV, MP4…

FLV vs. MKV — Format Comparison

Know what you are converting and why

Feature	FLV	MKV
Developer	Adobe (Macromedia, 2002)	Matroska.org / open standard (2002)
Common codecs	Sorenson Spark, On2 VP6, H.264	H.264, H.265, AV1, VP9, AAC, FLAC
Browser support	None (Flash ended 2020)	Limited (use MP4 for web)
Multiple audio tracks	No	Yes — unlimited tracks
Embedded subtitles	No	Yes — SRT, ASS, PGS, VobSub
Media server support	Not supported	Plex, Jellyfin, Emby native

FFmpeg (Recommended — full codec control)

Free, cross-platform, most flexible

FFmpeg handles all FLV variants. If your FLV contains H.264 video and AAC or MP3 audio, use -c copy for a lossless container rewrap. For Sorenson Spark or VP6 sources, re-encode to H.264 with libx264.

# Install on Mac via Homebrew
brew install ffmpeg

# Install on Windows via winget
winget install ffmpeg

# Check FLV codec before converting
ffprobe -v quiet -show_streams -select_streams v:0 input.flv

# Lossless rewrap (only if FLV contains H.264 + AAC/MP3)
ffmpeg -i input.flv -c copy output.mkv

# Re-encode Sorenson Spark or VP6 FLV to H.264 MKV
ffmpeg -i input.flv -c:v libx264 -crf 22 -c:a aac -b:a 192k output.mkv

# High quality H.265 MKV (smaller file, slower encode)
ffmpeg -i input.flv -c:v libx265 -crf 24 -c:a aac -b:a 192k output.mkv

# Batch convert all FLV files in a folder to MKV
for f in *.flv; do ffmpeg -i "$f" -c copy "${f%.flv}.mkv"; done

CRF 18 = near-lossless (larger file). CRF 28 = smaller file with more compression. CRF 22 is a good default for most FLV archive content.

HandBrake (GUI — quality-focused encoding)

Free, Windows / Mac / Linux

Download and open HandBrake from handbrake.fr.
Drag your FLV file onto the HandBrake window to load it as the source.
In the Summary tab, set Format to MKV.
Choose a preset — Fast 1080p30 or Fast 720p30 works well for most FLV files.
In the Video tab, set the encoder to H.264 (x264) and set the RF quality slider (RF 20 is a good default; lower = higher quality).
In the Audio tab, set the encoder to AAC and bitrate to at least 128 kbps.
Optionally add subtitle tracks in the Subtitles tab — MKV supports embedded SRT and SSA/ASS.
Click Browse to set a destination MKV file, then click Start Encode.

VLC Media Player (GUI — no command line)