What is an RF64 file?
The RF64 format has a maximum file size of 4 GB and is compatible with BWF. In Winamp, this format is called RIFF64 broadcast wave. Winamp is a multimedia playback software for Microsoft Windows. The RF64 store’s audio data in RIFF64 in broadcast wave format. Being a multichannel audio file format the RF64 is primarily designed to remove size restrictions on other file formats allowing users to store files over 4GB. This file format add metadata to the sound data to enable its exchange between platforms and applications.
Moreover, RF64 is an open format allowing users to broadcast large files, document their activities, and supports timecode to enable synchronization with other recordings. Using the RF64 extension you can easily create Broadcast Wave Files which will contain the “bext” chunk from the BWF specification
RF64 File Format
RF64 can store stereo downmix channels and bitstream data that was not encoded in PCM. This file format can be used throughout the entire workflow, from recording to editing and playback of material, and for long-term or short-term archiving.
Since CUE chunk definitions are inconsistently used, LABL chunk names need to be included in an additional chunk, and CUE chunk pointer indexes are restricted to 32 bits, the 2009 RF64 format also defines an additional ‘r64m’ marker chunk.
As the RF64 file format evolves, it is likely to meet the long-term requirements of broadcasting and archiving. It requires a relatively small amount of software implementation work and will require reasonable changes in existing systems.
Brief History
The European Broadcasting Union developed the RF64 file format, a multichannel audio format that is compatible with BWF. It is based on Microsoft RIFF/WAV format and Wave Format Extensible for multichannel purposes. It has also been accepted as the ITU recommendation ITU-R
Format Specifications
A new ‘ds64’ chunk is immediately inserted (before the FMT chunk), after the 32-bit chunk size field at offset 4 is set to -1 (0xFFFFFFFF) in RF64 simplest form. By using a simple sequential table mechanism, the DS64 chunk will contain the data chunk(s), pointing to additional DATA chunks. The first 4 bytes of the file are then being changed from ‘RIFF’ to ‘BW64’.
Additional chunks defined by RF64 files include:
- BW64 : Replacing “RIFF”
- ds64 : 64-bit data size, first chunk under BW64
- axml : Replaced by BW64
- bxml : Similar to “axml” in BWF (ITU-R BS.1352-3), but it is compressed
- sxml : XML data related to sound
- chna : Info of the channel
- JUNK : ds64 placeholder
