[FFmpeg-devel] aptX codec in RIFF wave container

[Pali Rohár]

Hello,

it looks like that audio encoded by aptX (non-hd) codec can be stored in
RIFF wave container. Look into old Microsoft Multimedia document named
"New Multimedia Data Types and Data Techniques" from April 15, 1994.

http://web.archive.org/web/20120917060438/http://download.microsoft.com/download/9/8/6/9863C72A-A3AA-4DDB-B1BA-CA8D17EFD2D4/RIFFNEW.pdf

It was available on Microsoft website, but now is only in webarchive.

At page 45 is described WAVE format header with allocated id for aptX.

#define WAVE_FORMAT_APTX (0x0025)

Description of compression on that page really matches aptX (non-hd)
codec which is already supported by ffmpeg.

So... could you add support for storing aptX encoded audio to RIFF wave
container? Currently ffmpeg can store aptX only into "raw" container, so
there is no information about frequency or channels. And above document
describe that frequency and number of channels can be stored in RIFF
wave also for aptX payload.

Below is copy of page 45 from that PDF document:

========================================================================

Audio Processing Technology Wave Type

Added: 06/22/93
Author: Calypso Software Limited

    Fact Chunk

This chunk is required for all WAVE formats other than WAVE_FORMAT_PCM. It stores file dependent
information about the contents of the WAVE data. It currently specifies the length of the data in samples.

    WAVE Format Header

    #define           WAVE_FORMAT_APTX                                           (0x0025)

        wFormatTag              This must be set to WAVE_FORMAT_APTX.
        nChannels               Number of channels in the wave, always 1 for mono, 2 for stereo.
        nSamplesPerSec          Frequency of the sample rate of the wave file. (8000, 11025, 22050, 44100,
                                48000)
        nAvgBytesPerSec         Average data rate..= nChannels * nSamplesPerSec/2. (16bit audio)
                                Playback software can estimate the buffer size using the <nAvgBytesPerSec>
                                value.
        nBlockAlign             Should be set to 2 (bytes) for mono data or 4 (bytes) for stereo.
                                For mono data 4 sixteen bit samples will be compressed into 1 sixteen bit
                                word
                                For stereo data 4 sizteen bit left channel samples will be compressed into the
                                first 16bit word and 4 sixteen bit right channel samples will be cmpressed into
                                the next 16 bit word.
                                Playback software needs to process a multiple of <nBlockAlign> bytes of data
                                at a time, so that the value of <nBlockAlign> can be used for buffer
                                alignment.
        wBitsPerSample          This is the number of bits per sample. Not used; set to four.
        cbSize                  The size in bytes of the extra information in the extended WAVE 'fmt'
                                header. This should be 0.(zero)

The definition of the data contained in the APTX format is considered proprietary information of Audio
Processing Technology Limited. They can be contacted at:

         Audio Processing Technology Limited
         Edgewater Road
         Belfast, Northern Ireland, BT3 9QJ
         Tel 44 232 371110
         Fax 44 232 371137

This format is proprietary audio format using 4:1 compression i.c. 16 bits of audio are compressed to 4
bits. It is only encoded/decoded by dedicated hardware from MM_APT

Multimedia Data Standards Update April 15, 1994       Page 45 of 73

========================================================================

-- 
Pali Rohár
pali.rohar at gmail.com
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