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OMX.broadcom.audio_mixer

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audio_mixer
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The conformant audio_mixer component accepts raw PCM audio frames from enabled input ports sums these onto frames emitted from the output port.

If necessary, input data is converted to match the PCM configuration of the output port at the mixdown stage (see the supported PCM formats). The mixer will perform sampling rate conversions, bitrate scaling and channel downmixing. However, at the moment, downmixing from 8 channels to 4 channels is not supported and only stereo input can be resampled (SW-3833).

The mixer provides a clock input port that can be used to ensure constant rate output regardless of input ports that fail to provide buffers in time to keep up with the output port frame rate.

The mixer output port can buffer up mixed output to be used for gapless and crossfaded audio track changes between input ports.

PortIndexNotes
231 232 233 234 235OMX_IndexParamPortDefinition Query / set the port parameters for the audio input/output streams. The audio format must not be encoded. nBufferSize must be a multiple of 32 and and equal to or larger than 1024. nBufferAlignment must be equal to or larger than 32.
OMX_IndexParamAudioPcm nChannels must be 1, 2, 4, or 8. 5.1 audio can be carried inside 8 channels, with the last two channels advertised as blank. eNumData must be OMX_NumericalDataSigned. eEndian must be OMX_EndianLittle. bInterleaved must be OMX_TRUE. nBitPerSample must be 16 or 32. nSamplingRate must be less or equal to 96000. ePCMMode must be OMX_AUDIO_PCMModeLinear.
OMX_IndexParamAudioPortFormat Query / set the audio port used on the port. Audio ports currently only support PCM format audio.
OMX_IndexConfigAudioMute Query / set the mute status of the port.
232 233 234 235OMX_IndexConfigAudioVolume Query / set the volume control for the input ports. This controls the software volume scaling that occurs prior to mixdown.
OMX_IndexConfigBrcmAudioTrackChangeControl Configure a gapless or an overlapping crossfaded track change from one input port to another using the output buffering mechanism in the mixer.
OMX_IndexConfigBrcmAudioTrackChangeCount Query the number of times the port has completed a track change. A track change is complete for an input port when a buffer flagged with OMX_BUFFERFLAG_EOS has been fully mixed into output port buffers as is ready to be returned or flushed from the input port. This configuration value can be monitored via OMX_IndexConfigRequestCallback.
OMX_IndexConfigRequestCallback Set whether we enable a callback to the client when the value of an index structure changes. Only supported for the index OMX_IndexConfigBrcmAudioTrackChangeCount.
230OMX_IndexParamPortDefinition Query / set the port parameter for the clock port. Only the number of buffers can be modified on this port.
OMX_IndexParamOtherPortFormat Query / set the port format for this clock port. This port currently only supports the time format.
 OMX_IndexConfigBrcmMinimumProcessingLatency Query/set the difference between the actual media time and when the mixer receives request fulfillments for media time requests.