.WAV File Format

Introduction

RIFX is the big-endian form of RIFF, and a RIFX WAVE file is a WAV file with every number stored most significant byte first. The 1991 RIFF specification from IBM and Microsoft defines it in one sentence: a RIFX file “is the same as a RIFF file, except that the first four bytes are ‘RIFX’ instead of ‘RIFF’, and integer byte ordering is represented in Motorola format”. The specification also says that no RIFX form types were defined at the time, and that registering a RIFF form does not register its RIFX counterpart.

It is rare. SciPy’s scipy.io.wavfile reads and writes it, and libsndfile and FFmpeg read it; few other programs do. The chunks are the ones of an ordinary RIFF WAVE file, but a reader that does not swap the byte order gets every size and every sample wrong, so it is a separate format; see all the WAV variations.

A file dropped on any page of this site opens in the explorer, which shows every chunk and field, read big-endian, and the waveform, which can be played.

Structure

A RIFX WAVE file is one outer chunk with the form type WAVE. Inside it sit further chunks, each a four-character ID, a 32-bit big-endian size and the data, padded to an even length. See RIFX chunks.

Two chunks are required: the format chunk fmt , which says how the audio is encoded, and the data chunk data, which holds the samples, also big-endian; see Sample data. Other chunks are optional metadata. Chunk IDs and other four-character codes are strings of bytes and read the same in either byte order.

Telling it apart

The explorer’s parser for this format checks two things: bytes 0 to 3 are RIFX and bytes 8 to 11 are WAVE. Nothing else turns a file down. After the header, every problem it finds is reported on the chunk where it occurs, and the rest of the file is still read.

A file that starts RIFF, RF64 or BW64 before WAVE is one of the other WAV formats.

Browsers cannot play RIFX files, so the explorer decodes the samples itself, swapping the byte order, for PCM, float, A-law, µ-law and the two ADPCM codecs.

Who writes it

RIFX WAVE files are met mostly in software tests. The only ones examined for this site are SciPy’s test files test-44100Hz-be-1ch-4bytes.wav, test-8000Hz-be-3ch-5S-24bit.wav and test-44100Hz-2ch-32bit-float-be.wav. SciPy writes RIFX when asked for big-endian output; libsndfile and FFmpeg read it.

Variants

• Waveform audio (RIFF) – the usual WAV file: little-endian chunks with 32-bit sizes
• Big-endian waveform audio (RIFX) – the same chunks with big-endian numbers
• EBU RF64 audio (RF64) – 64-bit sizes in a ds64 chunk, for files over 4 GB
• ITU-R BW64 audio (BW64) – RF64’s layout with Audio Definition Model metadata

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