Name

    AL_SOFT_direct_channels_remix

Contributors

    Chris Robinson

Contact

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

Status

    Complete

Dependancies

    This extension is written against the OpenAL 1.1 specification.
    This extension depends on AL_SOFT_direct_channels.
    This extension interacts with AL_EXT_BFORMAT.

Overview

    This extension adds the ability to remix channels to the
    AL_SOFT_direct_channels extension. By default, that extension drops input
    buffer channels that don't have a matching output channel. This really only
    works well for controlled setups where the input and output are known, but
    problems arise when these become variable. An option to remix input
    channels to the closest output channels will ensure the sound will still be
    audible with as little virtualization as possible.

Issues

    Q: How does this extension maintain compatibility with
       AL_SOFT_direct_channels?
    A: Originally, the AL_DIRECT_CHANNELS_SOFT property accepted AL_FALSE and
       AL_TRUE, which are 0 and 1 respectively. This extension supplies the
       new AL_DROP_UNMATCHED_SOFT enum name with the same value as AL_TRUE,
       providing the same behavior as the original extension, while the other
       new enum name, AL_REMIX_UNMATCHED_SOFT, has the value 2 which would
       previously cause an error, but now enables the new behavior.

New Procedures and Functions

    None.

New Tokens

    Accepted as the <value> parameter of alSourcei and alSourceiv for the
    AL_DIRECT_CHANNELS_SOFT property:

        AL_DROP_UNMATCHED_SOFT                   0x0001 /* same as AL_TRUE */
        AL_REMIX_UNMATCHED_SOFT                  0x0002

Additions to Specification

    Modify Table 4.x, Channel Virtualization

    Name                       Signature  Values                    Default
    -------------------------  ---------  ------------------------  ----------
    AL_DIRECT_CHANNELS_SOFT    i, iv      AL_REMIX_UNMATCHED_SOFT,  AL_FALSE
                                          AL_DROP_UNMATCHED_SOFT,
                                          AL_FALSE

    Description:
    AL_DIRECT_CHANNELS_SOFT set to AL_DROP_UNMATCHED_SOFT indicates the audio
    channels are not virtualized and play directly on the matching output
    channels if they exist, otherwise they are dropped. When set to
    AL_REMIX_UNMATCHED_SOFT, the audio channels are not virtualized and play
    directly on the matching output channels if they exist, otherwise they are
    remixed to the closest available channels. Applies only when playing non-
    mono and non-B-Format buffers.