Free online WEBM to FLV converter

Older Flash-based players, legacy streaming servers, and some editing systems accept FLV but not WEBM. Converting is necessary when the receiving application requires an FLV container and compatible H.264/AAC streams rather than simply a different filename extension.

What the WEBM format is

WEBM is an open audiovisual container designed mainly for web playback. It commonly stores VP8 or VP9 video with Vorbis or Opus audio, although the container can hold other codec combinations. Modern browsers, screen-recording tools, video-conferencing applications, and web media frameworks commonly create WEBM files.

WEBM is well supported by current browsers and media players, but older broadcast, editing, surveillance, and Flash-era systems may not recognize its container or codecs. Changing .webm to .flv does not convert the streams.

What the FLV format is

FLV, or Flash Video, is a container originally designed for Adobe Flash Player and older HTTP or streaming-server workflows. It commonly carries H.264/AVC video with AAC audio; older files may contain Sorenson Spark or VP6 video with MP3 audio.

Its practical advantage is compatibility with a specific legacy application or server that explicitly requires FLV. It does not provide better quality than WEBM, and it is unsuitable for most new web projects because Adobe Flash Player reached end of support in 2020.

How to convert WEBM to FLV with FFmpeg

FFmpeg provides direct control over the codecs, bitrate, frame rate, and FLV container. Install FFmpeg, open a terminal in the folder containing the source file, and run:

ffmpeg -i input.webm -c:v libx264 -preset medium -crf 23 -pix_fmt yuv420p -c:a aac -b:a 128k -f flv output.flv

Replace input.webm and output.flv with the actual filenames. FFmpeg decodes the WEBM streams, re-encodes the video as H.264 and the audio as AAC, then writes an FLV file. A CRF value around 18–23 is typical for general-purpose H.264 output; lower values increase quality and file size.

To target a file size or bandwidth limit, use fixed bitrates instead:

ffmpeg -i input.webm -c:v libx264 -b:v 1500k -c:a aac -b:a 96k -f flv output.flv

Inspect the source and result with:

ffprobe input.webm
ffprobe output.flv

For an occasional conversion without installing software, the file can be converted for free on 101convert.com: upload the WEBM file, select FLV, start the conversion, and download the result. Do not upload confidential recordings unless the service’s retention and handling terms are acceptable.

HandBrake is not a dependable FLV option: its standard current output targets are MP4, MKV, and WEBM rather than FLV. FFmpeg is the more suitable desktop choice when FLV output is required.

Quality and compatibility limits

Because the conversion normally decodes and re-encodes both streams, it causes generation loss. Keep the original WEBM as the archive master, and use a high-quality source when producing the FLV.

Use H.264 and AAC for broad FLV compatibility; leaving VP9 or Opus unchanged will not make those streams usable in an older FLV player. Some legacy players also impose limits on H.264 profile, level, resolution, bitrate, sample rate, or frame rate. If the basic output fails, try a more conservative command:

ffmpeg -i input.webm -c:v libx264 -profile:v baseline -level 3.0 -r 30 -pix_fmt yuv420p -c:a aac -ar 44100 -b:a 128k -f flv output.flv

This setting forces 30 frames per second and 44.1 kHz audio, which may improve compatibility but can alter timing or motion. Subtitles, transparency, multiple audio tracks, chapters, variable-frame-rate behavior, and modern HDR metadata may not survive or may not be supported by the FLV container or target software. Test the output in the application that will use it, checking duration, synchronization, seeking, resolution, and audio playback.