Name

    AL_SOFT_UHJ_ex

Contributors

    Chris Robinson

Contact

    Chris Robinson (chris.kcat 'at' gmail.com)

Status

    Complete.

Dependencies

    This extension is for OpenAL 1.1.
    This extension requires AL_SOFT_UHJ.
    This extension requires one or more of AL_EXT_MULAW, AL_EXT_ALAW,
    AL_EXT_IMA4, and AL_SOFT_MSADPCM.
    This extension interacts with AL_SOFT_block_alignment.

Overview

    This extension supplements AL_SOFT_UHJ by adding muLaw, aLaw, IMA4, and
    MSADPCM sample types to UHJ formats. The base AL_SOFT_UHJ extension could
    already use these formats (when available) for Super Stereo processing,
    and this extension allows them to be used for UHJ itself too.

Issues

    Q: Why are IMA4 and MSADPCM only available for 2-channel UHJ and not 3- or
       4-channel?
    A: IMA4 and MSADPCM only seem to supoort 1 and 2 channels. FFmpeg only
       supports creating 1- and 2-channel IMA4 and MSADPCM files, and its
       decoder behaves oddly when its given more than 2. And libsndfile only
       handles 1 and 2 channels. I don't know why the data interleaving for 2
       channels can't simply be extended to more channels, but if other
       libraries are hesitant to do it, it's best to avoid making the
       assumption.

    Q: Are muLaw, aLaw, IMA4, and MSADPCM all required?
    A: Not for implementations that don't already support them. If an
       implementation supports AL_EXT_MULAW, then the added muLaw formats will
       be supported, but if not, then they aren't. Same for aLaw/AL_EXT_ALAW,
       IMA4/AL_EXT_IMA4, and MSADPCM/AL_SOFT_MSADPCM.

New Procedures and Functions

    None.

New Tokens

    Accepted by the <format> parameter of alBufferData if AL_EXT_MULAW is also
    supported:

        AL_FORMAT_UHJ2CHN_MULAW_SOFT             0x19B3
        AL_FORMAT_UHJ3CHN_MULAW_SOFT             0x19B7
        AL_FORMAT_UHJ4CHN_MULAW_SOFT             0x19B9

    Accepted by the <format> parameter of alBufferData if AL_EXT_ALAW is also
    supported:

        AL_FORMAT_UHJ2CHN_ALAW_SOFT              0x19B4
        AL_FORMAT_UHJ3CHN_ALAW_SOFT              0x19B8
        AL_FORMAT_UHJ4CHN_ALAW_SOFT              0x19BA

    Accepted by the <format> parameter of alBufferData if AL_EXT_IMA4 is also
    supported:

        AL_FORMAT_UHJ2CHN_IMA4_SOFT              0x19B5

    Accepted by the <format> parameter of alBufferData if AL_SOFT_MSADPCM is
    also supported:

        AL_FORMAT_UHJ2CHN_MSADPCM_SOFT           0x19B6

Additions to Specification

    UHJ Buffer Formats

    The formats AL_FORMAT_UHJ2CHN_MULAW_SOFT, AL_FORMAT_UHJ2CHN_ALAW_SOFT,
    AL_FORMAT_UHJ2CHN_IMA4_SOFT, AL_FORMAT_UHJ2CHN_MSADPCM_SOFT,
    AL_FORMAT_UHJ3CHN_MULAW_SOFT, AL_FORMAT_UHJ3CHN_ALAW_SOFT,
    AL_FORMAT_UHJ4CHN_MULAW_SOFT, and AL_FORMAT_UHJ4CHN_ALAW_SOFT may be used
    for buffering data to functions like alBufferData.

    muLaw and aLaw data are decompressed to 16-bit samples according to the
    AL_EXT_MULAW and AL_EXT_ALAW extensions.

    IMA4 and MSADPCM data are decompressed to 16-bit samples according to the
    AL_EXT_IMA4 and AL_SOFT_MSADPCM extensions. As block-based formats, they
    are also affected by the AL_SOFT_block_alignment extension's block
    alignment properties, when supported.

Errors