Convert RMVB to CAF — Free Online Tool
Convert RMVB video files to Apple's Core Audio Format (CAF), extracting and transcoding the audio stream to uncompressed PCM (16-bit) — ideal for bringing legacy RealMedia audio into Apple-native workflows or professional audio pipelines that require high-fidelity, lossless audio storage.
to
FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
Drop your RMVB file here
or click to browse
Free — no uploads, no signups. Your files never leave your browser.
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
RMVB files typically contain video encoded with RealVideo and audio encoded with AAC or other RealAudio codecs inside RealNetworks' variable-bitrate container. During this conversion, FFmpeg discards the video stream entirely and decodes the audio track, then re-encodes it as 16-bit little-endian PCM (pcm_s16le) wrapped in Apple's CAF container. Because PCM is uncompressed, the audio is stored at full fidelity with no further lossy compression applied — though any quality loss from the original RMVB's lossy audio codec is already baked in and cannot be recovered. The CAF container itself is purpose-built by Apple to support large files and a broad range of audio codecs, making it a robust destination for archival or further processing in Logic Pro, Core Audio APIs, or other Apple ecosystem tools.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary — the open-source multimedia processing engine that handles demuxing the RMVB container, decoding the RealAudio stream, and encoding the output to CAF. |
-i input.rmvb
|
Specifies the input file in RMVB format. FFmpeg reads the variable-bitrate RealMedia container, identifying the audio and video streams inside it. |
-c:a pcm_s16le
|
Sets the output audio codec to 16-bit signed little-endian PCM — uncompressed audio that stores raw sample values with no lossy compression, making it natively compatible with Apple's Core Audio framework and CAF container. |
-b:a 128k
|
Nominally sets an audio bitrate target of 128 kbps, but this flag has no practical effect on pcm_s16le since PCM bitrate is fixed by sample rate and bit depth rather than a compression target — it can be omitted when running this command locally. |
output.caf
|
Defines the output filename and signals FFmpeg to wrap the PCM audio stream in Apple's Core Audio Format container, which supports large file sizes and is natively consumed by macOS and iOS audio APIs. |
Common Use Cases
- Extracting the audio commentary or dialogue track from an old RMVB-format film or lecture to import into Logic Pro or GarageBand for editing
- Archiving the audio from legacy RMVB video downloads into an uncompressed CAF file before further mastering or noise reduction in an Apple-native DAW
- Preparing audio extracted from RMVB-encoded online course videos for use in iOS or macOS apps that natively consume CAF files via Core Audio
- Converting RMVB episode audio tracks to CAF as an intermediate step before re-encoding to ALAC or AAC for an Apple Music library
- Stripping and preserving the audio from RMVB-format sports broadcasts or archived streaming content in a format compatible with Apple's AVFoundation framework
- Recovering audio from RMVB files where the video codec is unsupported on modern systems but the audio content still has value
Frequently Asked Questions
The conversion involves one decode step: the original lossy audio in the RMVB (typically AAC or a RealAudio variant) is decoded and written out as uncompressed 16-bit PCM in the CAF file. You will not lose any additional quality beyond what was already lost when the RMVB was originally encoded — PCM introduces no further compression artifacts. However, any quality ceiling is set by the source RMVB's audio bitrate, so this process does not 'restore' detail that the original lossy codec discarded.
RMVB uses lossy audio compression (and also contains a video stream), so it stores audio in a highly compact form. CAF with pcm_s16le stores raw, uncompressed audio samples — CD-quality stereo at 44.1 kHz uses roughly 10 MB per minute. Since the RMVB file compressed both audio and video together, the extracted uncompressed audio-only CAF can easily be several times larger than the original file, especially for longer recordings.
CAF does not support any RealAudio codec — its supported codecs include PCM variants, AAC, FLAC, Opus, and Vorbis. This means the audio must always be fully decoded and re-encoded during this conversion; there is no stream-copy option available. FFmpeg handles this automatically by decoding the RMVB audio and encoding it to pcm_s16le for the CAF output.
RMVB files store metadata in RealNetworks' proprietary format, and FFmpeg's ability to map this to CAF metadata tags is limited. Most embedded metadata — such as title, author, or copyright fields — is unlikely to transfer reliably into the CAF output. If metadata preservation is critical, you should inspect and re-tag the output CAF file using a tool like Apple's afinfo or a metadata editor that supports CAF.
Yes. CAF supports several codecs including AAC, FLAC, libopus, and libvorbis. To use AAC instead of PCM, change -c:a pcm_s16le to -c:a aac in the FFmpeg command. For a lossless but compressed output, use -c:a flac. PCM is the default because it guarantees maximum compatibility with Apple's Core Audio APIs and avoids any additional lossy encoding step on already-compressed RMVB audio.
For PCM codecs like pcm_s16le, bitrate flags like -b:a have no effect — quality is determined entirely by the bit depth (16-bit) and the sample rate inherited from the source. To increase bit depth, replace pcm_s16le with pcm_s24le (24-bit) or pcm_s32le (32-bit): for example, ffmpeg -i input.rmvb -c:a pcm_s24le output.caf. If you switch to a codec like AAC or Opus, the -b:a flag (e.g., -b:a 192k) then controls the output bitrate meaningfully.
Technical Notes
RMVB (RealMedia Variable Bitrate) is a container that predates most modern formats and uses proprietary RealVideo and RealAudio codecs not natively supported on Apple platforms. FFmpeg can demux and decode these streams, but because CAF has no support for any RealAudio codec, a full audio transcode is unavoidable — there is no fast stream-copy path for this conversion. The default output codec, pcm_s16le, produces standard CD-resolution 16-bit audio, which is compatible with virtually all Apple tools including Core Audio, AVFoundation, Logic Pro, and GarageBand. One known limitation is that RMVB files with multiple audio streams (rare but possible) will have only the first audio track extracted by default. CAF itself supports large file sizes beyond the 4 GB limit of WAV and AIFF, making it suitable for archiving long recordings. Since RMVB does not support chapters or subtitle tracks in a way FFmpeg maps to standard streams, no chapter or subtitle data will appear in the CAF output. The -b:a 128k flag in the command is effectively a no-op for pcm_s16le since PCM bitrate is determined by sample rate and bit depth, not a target bitrate — it can be safely omitted when running the command locally.