Convert FLV to WMV — Free Online Tool
Convert FLV files to WMV by transcoding from H.264/AAC (the dominant FLV codec pair) into Microsoft's MPEG-4 v2 video codec wrapped in an ASF container with WMA audio — making Flash-era video files compatible with Windows Media Player and legacy Windows software.
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FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
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Note: Browser-based encoding uses approximate quality targets. For precise CRF compression, copy the FFmpeg command above and run it on your desktop.
Estimated output:
Conversion Complete!
DownloadHow It Works
FLV files typically carry H.264 video and AAC audio, both of which must be fully re-encoded during this conversion — there is no stream-copy shortcut available because WMV uses the ASF container with Microsoft's own MPEG-4 variant (msmpeg4) for video and WMA v2 (wmav2) for audio. FFmpeg decodes every frame and audio sample from the FLV source, then re-encodes them using the msmpeg4 and wmav2 codecs, writing the result into an ASF file with the .wmv extension. The `-f asf` flag is required because FFmpeg cannot infer the ASF container format from the .wmv extension alone. Because both the video and audio streams are transcoded (not remuxed), some generation loss is inherent, and the output file size is governed by the target video bitrate (2000k by default) rather than the source FLV's CRF-based quality setting.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary, the open-source multimedia processing engine that powers both this browser-based tool (via WebAssembly) and local desktop conversions. |
-i input.flv
|
Specifies the input FLV file. FFmpeg reads the ASF-incompatible Flash Video container, demuxing the H.264 video and AAC audio streams for re-encoding into WMV-compatible codecs. |
-c:v msmpeg4
|
Sets the video codec to Microsoft MPEG-4 version 3 (msmpeg4), the standard video codec for WMV files and the format natively understood by Windows Media Player without additional codec installations. |
-c:a wmav2
|
Sets the audio codec to Windows Media Audio v2 (wmav2), Microsoft's standard lossy audio format for WMV/ASF containers, replacing the AAC audio track from the source FLV. |
-b:v 2000k
|
Sets the target video bitrate to 2000 kilobits per second for the msmpeg4 encoder. Unlike the FLV source which uses CRF-based quality, WMV encoding relies on a fixed bitrate target — 2000k is suitable for standard-definition content; HD FLV sources may require 4000k or higher to maintain acceptable quality. |
-b:a 128k
|
Sets the WMA v2 audio bitrate to 128 kilobits per second, a standard quality level that produces clear stereo audio comparable to 128k AAC in the source FLV at a similar file size contribution. |
-f asf
|
Explicitly instructs FFmpeg to use the ASF (Advanced Systems Format) container muxer. This flag is mandatory because FFmpeg cannot infer the ASF format from the .wmv file extension alone — without it, the output file will be invalid or FFmpeg will throw a muxer error. |
output.wmv
|
Specifies the output filename with the .wmv extension. Combined with the `-f asf` flag, this produces a properly formatted Windows Media Video file ready for playback in Windows Media Player and compatible software. |
Common Use Cases
- Making archived Flash video content from the pre-HTML5 era playable in Windows Media Player on older corporate or government Windows workstations that lack modern codec packs.
- Submitting video files to legacy Windows-based content management systems or digital asset platforms that only accept WMV/ASF format input.
- Converting FLV recordings captured from older screen-recording or webinar tools into a format compatible with Windows Movie Maker for further editing.
- Delivering video content to clients or partners in industries (legal, medical, government) that standardized on Windows Media infrastructure and require WMV for archival workflows.
- Repurposing FLV video files downloaded from early-2000s or 2010s websites for inclusion in Windows-based interactive kiosk or presentation software that requires WMV playback.
- Preparing FLV source footage for ingestion into video platforms or encoding pipelines that accept WMV but not FLV as an upstream format.
Frequently Asked Questions
Yes, some quality loss is unavoidable because this conversion requires full re-encoding of both the video and audio streams — the H.264 video in the FLV is decoded and re-encoded using the msmpeg4 codec, which is a generation-older codec than H.264 and generally less efficient at the same bitrate. At the default 2000k video bitrate, most standard-definition FLV content will look acceptable, but high-definition FLV files may show more visible degradation. If quality is a priority, increase the video bitrate (e.g., to 4000k or 6000k) to compensate for msmpeg4's lower compression efficiency.
FFmpeg does not automatically recognize .wmv as the ASF container format, so the `-f asf` flag is required to explicitly tell FFmpeg to use the ASF (Advanced Systems Format) muxer. Without this flag, FFmpeg may fail or produce a malformed output file. WMV is effectively a branded name for video content stored in an ASF container, so specifying `-f asf` is the correct and necessary way to produce a valid .wmv file.
Neither FLV nor the WMV/ASF container produced by this conversion supports subtitles or chapters, so no subtitle or chapter data will be present in either the input or output. If your FLV contains embedded metadata (title, author, etc.), that metadata is not guaranteed to transfer to the ASF container during this conversion. The WMV format does support multiple audio tracks in ASF, but since FLV does not support multiple audio tracks, this feature is irrelevant for single-track FLV sources.
Replace the `-b:v 2000k` value in the command with your desired bitrate. For a smaller file with lower quality, try `-b:v 500k` or `-b:v 1000k`. For higher quality output from an HD FLV source, use `-b:v 4000k` or `-b:v 6000k`. Unlike the FLV input which uses CRF-based quality control (where quality is constant and bitrate varies), WMV encoding via msmpeg4 uses a fixed target bitrate, so choosing the right `-b:v` value is the primary lever for balancing file size against visual quality.
Yes. On Windows, you can loop through FLV files using a batch script: `for %f in (*.flv) do ffmpeg -i "%f" -c:v msmpeg4 -c:a wmav2 -b:v 2000k -b:a 128k -f asf "%~nf.wmv"`. On Linux or macOS, use: `for f in *.flv; do ffmpeg -i "$f" -c:v msmpeg4 -c:a wmav2 -b:v 2000k -b:a 128k -f asf "${f%.flv}.wmv"; done`. The browser-based tool processes one file at a time, so the FFmpeg command is especially valuable for batch workflows involving large collections of FLV files.
The msmpeg4 codec (specifically MPEG-4 Part 2, Microsoft variant 3) has been supported by Windows Media Player since WMP 9, which covers virtually all Windows XP-era and later systems. It is one of the most broadly compatible codecs for Windows-native playback without requiring additional codec pack installation. However, msmpeg4 is not compatible with modern non-Windows players by default, so if your target audience uses VLC or similar cross-platform software, any modern format would be preferable to WMV.
Technical Notes
The FLV-to-WMV conversion involves two codec generations with meaningfully different compression characteristics. FLV's default H.264 video codec (libx264) is significantly more efficient than WMV's msmpeg4 (a Microsoft-proprietary MPEG-4 Part 2 variant), meaning you will typically need a higher bitrate in the WMV output to match the visual quality of the FLV source. The ASF container wrapping the WMV output also has structural overhead compared to FLV. On the audio side, AAC (used in FLV) and WMA v2 (wmav2, used in WMV) are broadly comparable in quality at 128k, though AAC has a slight technical advantage at lower bitrates. FLV does not support transparency, subtitles, or chapters, and neither does this WMV output profile, so there is no feature regression on those dimensions. One notable WMV/ASF capability not available in FLV is DRM support — ASF was designed with Windows Media DRM in mind — but this FFmpeg conversion does not apply any DRM. The `-f asf` flag is non-optional and must always accompany WMV output from FFmpeg; omitting it will cause muxer errors.