Convert WMV to RMVB — Free Online Tool
Convert WMV files to RMVB format by re-encoding the Microsoft proprietary MPEG-4 video stream using the modern H.264 (libx264) codec inside a RealMedia Variable Bitrate container. This is especially useful for bringing legacy Windows Media content into a format associated with compressed video distribution common in East Asian media libraries.
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FFmpeg Command
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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
WMV files use Microsoft's ASF (Advanced Systems Format) container, typically encoding video with msmpeg4 or msmpeg4v2 — Microsoft's proprietary MPEG-4 variants — and audio with WMA v2 (wmav2). Neither of these codecs is compatible with the RMVB container, so this conversion requires a full transcode of both streams. The video is decoded from msmpeg4 and re-encoded using libx264, which produces H.264 video at a CRF of 23 — a perceptually efficient quality level. The WMA audio is simultaneously decoded and re-encoded to AAC at 128k bitrate, as AAC is the supported audio codec for this output. The result is an RMVB file that leverages H.264's superior compression efficiency compared to the original Microsoft MPEG-4 codec, typically yielding better visual quality at similar or smaller file sizes.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary to begin processing. All subsequent flags define the input, transformations, and output for this WMV-to-RMVB conversion. |
-i input.wmv
|
Specifies the input file — a WMV file using Microsoft's ASF container, typically containing msmpeg4 or msmpeg4v2 video and wmav2 audio. FFmpeg will demux and decode both streams for transcoding. |
-c:v libx264
|
Re-encodes the video stream using the libx264 H.264 encoder, replacing the source Microsoft MPEG-4 codec with a modern, highly efficient standard that is compatible with the RMVB container and most modern players. |
-c:a aac
|
Transcodes the audio from WMA v2 (wmav2) to AAC, which is required because RMVB does not support Windows Media Audio. AAC provides good perceptual quality at the target bitrate and is compatible with RMVB playback. |
-crf 23
|
Sets the H.264 Constant Rate Factor to 23, FFmpeg's default, which targets a perceptually balanced quality level for the re-encoded video. Lower values (e.g., 18) produce larger, higher-quality files; higher values (e.g., 28) produce smaller files with more compression artifacts. |
-b:a 128k
|
Sets the AAC audio bitrate to 128 kilobits per second, which is a standard quality level suitable for most video audio content including speech and music found in WMV source files. |
output.rmvb
|
Defines the output filename with the .rmvb extension, which signals FFmpeg to write the result in the RealMedia Variable Bitrate container format encapsulating the newly encoded H.264 video and AAC audio streams. |
Common Use Cases
- Importing legacy WMV recordings into media players or devices that support RMVB but lack Windows Media codec support, such as certain standalone media players common in Asian markets
- Archiving or sharing older Windows Media Player-encoded video content with communities or platforms that distribute compressed video in RMVB format
- Reducing file sizes of WMV screen recordings or webcam captures by leveraging H.264's superior compression over Microsoft's MPEG-4 variant inside the RMVB container
- Converting DRM-free WMV home video or promotional content for distribution through channels or audiences that prefer the RMVB format
- Preparing WMV footage for playback on media centers or set-top boxes that have native RMVB support but do not include Windows Media codec packs
Frequently Asked Questions
Yes — this is a lossy-to-lossy transcode, meaning both the input WMV and the output RMVB use lossy compression. The original WMV video encoded with msmpeg4 is fully decoded and then re-encoded with libx264 at CRF 23, which introduces a second generation of compression artifacts. That said, H.264 at CRF 23 is generally more efficient than Microsoft's MPEG-4 codec, so the output can often match or exceed the perceived quality of the source at a similar or smaller file size. To minimize quality loss, lower the CRF value (e.g., to 18) for higher-quality H.264 output.
While historically RMVB files used RealNetworks' own RealVideo codec, modern FFmpeg does not support encoding to RealVideo, and that codec is largely obsolete. The practical standard today is to use H.264 (libx264) as the video codec within the RMVB container, which is widely accepted by players that support RMVB such as RealPlayer and many media centers. This approach gives you the file container expected while using a vastly superior and broadly compatible video codec.
The WMA v2 (wmav2) audio found in the source WMV file must be fully transcoded because RMVB does not support WMA audio. It is re-encoded to AAC at 128k bitrate, which is the default audio codec for this output. AAC at 128k delivers good perceptual quality for speech and typical video audio content. If the source WMV had stereo audio, this will be preserved in the AAC output track.
No — RMVB is a limited container in this respect. It does not support multiple audio tracks, subtitles, or chapter markers. WMV files technically support multiple audio tracks, so if your source WMV contains more than one audio track, only the first (default) audio track will be included in the RMVB output. Any subtitle streams or chapter data in the WMV will also be dropped during conversion.
The video quality is controlled by the -crf flag, which uses H.264's Constant Rate Factor scale ranging from 0 (lossless) to 51 (worst quality). The default is 23, which is a good balance of quality and file size. To increase quality, lower the CRF value — for example, use '-crf 18' for near-transparent quality or '-crf 28' for a smaller file with more compression. You can also adjust the audio bitrate with '-b:a', for example replacing '128k' with '192k' for higher-fidelity audio.
Yes — on Linux or macOS you can run a shell loop such as: for f in *.wmv; do ffmpeg -i "$f" -c:v libx264 -c:a aac -crf 23 -b:a 128k "${f%.wmv}.rmvb"; 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.rmvb". This is particularly valuable for large collections or files over 1GB, since the browser tool has a 1GB per-file limit.
Technical Notes
The WMV to RMVB conversion involves two codec families with very different lineages. WMV's msmpeg4 video codec is a Microsoft-modified variant of MPEG-4 Part 2 that is not fully standards-compliant, meaning it cannot be directly reused inside an RMVB container — a full decode-and-reencode cycle is mandatory. The output H.264 stream produced by libx264 is significantly more compression-efficient than msmpeg4, so file sizes may actually decrease at equivalent perceptual quality. Note that RMVB (as implemented here) does not carry the variable bitrate scheduling metadata of original RealNetworks-produced files; the container format is used for compatibility purposes. WMV files may carry DRM (Digital Rights Management) protection, and FFmpeg cannot process DRM-protected files — only DRM-free WMV files can be converted. The ASF container's special flags (-f asf) used when writing WMV are not needed for this output. No subtitle, chapter, or secondary audio track data survives this conversion due to RMVB container limitations.