Convert WMV to FLV — Free Online Tool
Convert WMV files to FLV format directly in your browser, transcoding the Microsoft MPEG-4 video stream to H.264 (libx264) and the WMA audio to AAC — producing a Flash Video file optimized for web delivery. This conversion is ideal for repurposing legacy Windows Media content for older web video pipelines or Flash-based players.
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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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Settings
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
WMV files use Microsoft's proprietary ASF container with video encoded in MS-MPEG-4 variants (msmpeg4 or msmpeg4v2) and audio in WMA (wmav2). Neither of these codecs is compatible with the FLV container, so this conversion requires a full transcode of both streams. The video is re-encoded from MS-MPEG-4 to H.264 using libx264, which offers significantly better compression efficiency and broader compatibility. The WMA audio is simultaneously transcoded to AAC, which is the standard audio codec supported by FLV when paired with H.264 video. The output is wrapped in Adobe's FLV container, historically used to deliver video via Adobe Flash Player on the web. Because both streams are fully re-encoded, processing time depends on the length and resolution of the source WMV file.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg tool, which handles the full transcode pipeline — reading the WMV's ASF container, decoding both the MS-MPEG-4 video and WMA audio, re-encoding them, and writing the FLV output. |
-i input.wmv
|
Specifies the input WMV file. FFmpeg reads the ASF container, identifying the MS-MPEG-4 video stream and the WMA (wmav2) audio stream for decoding and subsequent re-encoding. |
-c:v libx264
|
Selects libx264 as the video encoder, transcoding the MS-MPEG-4 video from the WMV into H.264 — the standard high-quality video codec supported by the FLV container, offering far better compression than Microsoft's MPEG-4 variant. |
-c:a aac
|
Selects AAC as the audio encoder, transcoding the WMA (wmav2) audio stream from the WMV into AAC, which is the preferred audio codec for FLV files paired with H.264 video and is required since WMA is not supported in the FLV container. |
-crf 23
|
Sets the Constant Rate Factor for the libx264 H.264 encode to 23, which is the default and provides a good balance between visual quality and file size. Lower values (e.g., 18) produce higher quality larger files; higher values (e.g., 28) produce smaller but more compressed output. |
-b:a 128k
|
Sets the AAC audio bitrate to 128 kbps, which is a standard quality level for AAC that replaces the WMA audio from the source WMV. This produces clear audio for most speech and music content within the FLV file. |
output.flv
|
Specifies the output filename and tells FFmpeg to write the re-encoded H.264 video and AAC audio into an FLV (Flash Video) container, the format historically used for web video delivery via Adobe Flash Player. |
Common Use Cases
- Repurposing archived WMV training videos or webinars for upload to legacy Flash-based corporate LMS platforms that only accept FLV input
- Converting Windows Media Player recordings or screen captures to FLV for embedding in older web applications built around JW Player or Flowplayer with Flash fallback
- Migrating a library of WMV promotional videos to FLV for use with a legacy Flash-based video gallery or e-commerce product page
- Preparing WMV footage captured from Windows-based video editors for delivery to a broadcast partner or client whose ingest system specifies FLV with H.264 video
- Converting WMV files downloaded from older Windows Media streaming servers into FLV for archival in a Flash-era digital asset management system
- Re-encoding DRM-free WMV content to FLV to feed into a legacy video processing pipeline that uses FFmpeg-based tools expecting Flash Video input
Frequently Asked Questions
Yes, some quality loss is inevitable because this conversion requires a full re-encode of both the video and audio streams. The source WMV is already lossy (using MS-MPEG-4 and WMA), so transcoding to H.264 and AAC introduces a second generation of compression artifacts. However, the default CRF value of 23 for libx264 typically produces very good visual quality at reasonable file sizes — in many cases, the H.264 output will look cleaner than the original MS-MPEG-4 encode at an equivalent bitrate. For critical quality preservation, lower the CRF value (e.g., to 18) to reduce compression.
No. WMV, via the ASF container, supports multiple audio tracks, but FLV is limited to a single audio stream. During this conversion, FFmpeg will select the default audio track from the WMV file and transcode it to AAC for the FLV output. If your source WMV contains multiple audio tracks (e.g., different language dubs), only the primary track will be included in the FLV. If you need a specific non-default track, you can modify the FFmpeg command with the '-map' flag to select it explicitly.
FLV has very limited metadata support compared to ASF/WMV, and it does not support embedded subtitles or chapter markers at all. Basic metadata such as title or author stored in the WMV may not carry over to the FLV output. Since WMV's subtitle and chapter data has no equivalent storage mechanism in the FLV container, that information is simply discarded during conversion. If subtitle preservation is important, you should consider converting to a container like MKV or MP4 instead.
The output file size depends heavily on the quality settings of both the source WMV and the FLV encode. If the original WMV was encoded at a high bitrate (e.g., 6000k or 8000k), the default CRF 23 H.264 encode in the FLV will likely be smaller, since H.264 is far more efficient than MS-MPEG-4 at equivalent quality levels. Conversely, if the WMV was encoded at a very low bitrate, the FLV output may be larger because the encoder targets a consistent quality level rather than a fixed file size. Adjust the CRF value in the FFmpeg command to directly control the tradeoff between quality and file size.
The video quality is controlled by the '-crf' flag in the command. CRF (Constant Rate Factor) ranges from 0 (lossless) to 51 (worst quality), with 23 as the default. To improve quality, lower the value — for example, '-crf 18' produces near-visually-lossless H.264 output at the cost of a larger file. To reduce file size at the expense of some quality, raise the value, such as '-crf 28'. You can also increase audio quality by changing '-b:a 128k' to '-b:a 192k' or '-b:a 256k' for richer AAC audio in the FLV output.
Yes. On Linux or macOS you can use a shell loop: 'for f in *.wmv; do ffmpeg -i "$f" -c:v libx264 -c:a aac -crf 23 -b:a 128k "${f%.wmv}.flv"; done'. On Windows Command Prompt, use: 'for %f in (*.wmv) do ffmpeg -i "%f" -c:v libx264 -c:a aac -crf 23 -b:a 128k "%~nf.flv"'. This applies the same H.264/AAC transcode to every WMV in the current directory, producing a corresponding FLV file for each. Batch processing on the desktop is especially useful for large WMV libraries that exceed the 1GB browser limit.
Technical Notes
WMV's ASF container uses Microsoft's proprietary MS-MPEG-4 video variants (msmpeg4 and msmpeg4v2), which are distinct from and incompatible with the standard MPEG-4 Part 2 codec — neither can be stream-copied into an FLV container, making a full video transcode mandatory. The FLV container officially supports H.264 (libx264) as its primary high-quality video codec and AAC as the paired audio codec, which is the combination used by this tool. One key limitation of FLV is that it does not support multiple audio tracks, so only the primary audio stream from the WMV source is carried through. WMV's DRM (Digital Rights Management) protection, if present, will prevent FFmpeg from reading the file entirely — this tool can only process DRM-free WMV content. The ASF container's streaming-oriented metadata and index structures are not preserved in FLV, and any embedded subtitle streams or chapter data in the WMV are dropped silently. Because H.264 is dramatically more efficient than MS-MPEG-4, a CRF 23 encode typically delivers equivalent or better visual quality at a lower bitrate than the original WMV, but the total file size will vary depending on the source encode's original bitrate and content complexity.