Free online FLV to WEBM converter

Older video players, editors, and web-publishing systems may reject an FLV file while accepting WEBM. Converting it can provide browser-compatible codecs and, with suitable encoding settings, a smaller file for sharing or web playback.

What the FLV format is

FLV (Flash Video) is a container developed for streaming video through Adobe Flash Player. Older streaming platforms, screen-recording programs, video download tools, and Flash-era publishing software commonly created .flv files. Flash Player reached end of support in 2020, so FLV is now mainly encountered in legacy media collections.

The .flv extension identifies the container, not the exact streams inside it. An FLV may contain Sorenson Spark, On2 VP6, or H.264 video and MP3 or AAC audio. VLC, FFmpeg, and MediaInfo can identify the codecs, resolution, frame rate, and audio tracks.

What the WEBM format is

WEBM is a web-focused, Matroska-based container intended for HTML5 video. Standard WebM files normally contain VP8, VP9, or AV1 video with Vorbis or Opus audio. Current versions of Chrome, Firefox, Edge, and other major browsers support common WebM combinations without Flash.

WebM is suitable for browser playback, HTML5 video, and web distribution. VP9 and AV1 can produce smaller files than older codecs at comparable visual quality, but encoding takes longer; AV1 playback and encoding can also require newer hardware. A conversion does not automatically reduce the file size: the result depends on the source, codec, resolution, frame rate, and quality settings.

How to convert the file

Using FFmpeg

FFmpeg provides the most control and runs on Windows, macOS, and Linux. Install a current build that includes libvpx and libopus, open a terminal in the source-file folder, and run:

ffmpeg -i input.flv -map 0:v:0 -map 0:a:0? -c:v libvpx-vp9 -crf 32 -b:v 0 -c:a libopus -b:a 128k output.webm

Replace input.flv and output.webm with the required filenames. This command re-encodes the first video and, if present, the first audio stream as VP9 and Opus. With VP9, -b:v 0 enables constant-quality mode; lower -crf values generally improve quality and increase file size. Values around 28–36 are reasonable starting points.

For faster encoding or compatibility with older WebM-capable software, use VP8 and Vorbis:

ffmpeg -i input.flv -map 0:v:0 -map 0:a:0? -c:v libvpx -crf 10 -b:v 1M -c:a libvorbis -q:a 5 output.webm

Here, -b:v 1M sets an approximate video bitrate target. Increase it for better quality and a larger file, or decrease it for a smaller file. To resize or set a frame rate, add options such as -vf scale=1280:-2 or -r 30; these changes can reduce quality or cause motion differences, so use them only when required.

Using 101convert.com

You can convert the file on 101convert.com for free without installing software. Select FLV as the source format and WEBM as the destination, upload the file, start the conversion, and download the result. Do not upload confidential material unless the service’s storage and processing terms are acceptable.

Quality and compatibility limits

Most FLV files require re-encoding because H.264, Sorenson Spark, or VP6 video and MP3 or AAC audio are not valid WebM streams. Re-encoding is lossy, so keep the original FLV when it is the only source copy. Converting a file cannot restore detail already lost through previous compression.

Open the output in a current browser or VLC and check duration, synchronization, resolution, subtitles, and audio tracks. Some target players support VP8 but not VP9, or Vorbis but not Opus; choose the corresponding codec if required. WebM also does not preserve every subtitle format, metadata field, embedded stream, or multi-track feature that an FLV may contain, so verify those separately.