Downmix

This API is intended for mixing of two audio files (streams), defined as the base audio file and the newcome audio file, into one output audio file.

The newcome audio file will be downmixed into the base audio file with individual gains applied to each file.

Illustration of Downmixing Process

The number of channel(s) of the output audio file will be the same with that of the base audio file. The number of channel(s) of the newcome audio file will also be changed to the same with the base audio file, if it is different from that of the base audio file.

The downmix process has 3 states:

  • Bypass Downmixing – Only the base audio file will be processed;
  • Switch on Downmixing – The base audio file and the target audio file will first enter the transition period, during which the gains of these two files will be changed from the original level to the target level; then enter the stable period, sharing a same target gain;
  • Switch off Downmixing – The base audio file and the target audio file will first enter the transition period, during which the gains of these two files will be changed back to their original levels; then enter the stable period, with their original gains, respectively. After that, the downmix process enters the bypass state.

Note that, the sample rates of the base audio file and the newcome audio file must be the same, otherwise an error occurs.

Application Example

Implementation of this API is demonstrated in advanced_examples/downmix_pipeline example.

API Reference

Functions

void downmix_set_input_rb_timeout(audio_element_handle_t self, int ticks_to_wait)

Sets the downmix timeout.

Parameters
  • self: audio element handle
  • ticks_to_wait: input ringbuffer timeout

void downmix_set_input_rb(audio_element_handle_t self, ringbuf_handle_t rb, int index)

Sets the downmix input ringbuffer. refer to ringbuf.h

Parameters
  • self: audio element handle
  • rb: handle of ringbuffer
  • index: The index of multi input ringbuffer.

esp_err_t downmix_set_output_type(audio_element_handle_t self, esp_downmix_output_type_t output_type)

Passes number of channels for output stream. Only supported mono and dual.

Return
ESP_OK ESP_FAIL
Parameters
  • self: audio element handle
  • output_type: down-mixer output type.

esp_err_t downmix_set_work_mode(audio_element_handle_t self, esp_downmix_work_mode_t mode)

Sets BYPASS, ON or OFF status of down-mixer.

Return
ESP_OK ESP_FAIL
Parameters
  • self: audio element handle
  • mode: down-mixer work mode.

esp_err_t downmix_set_out_ctx_info(audio_element_handle_t self, esp_downmix_out_ctx_type_t out_ctx)

Passes content of per channel output stream by down-mixer.

Return
ESP_OK ESP_FAIL
Parameters
  • self: audio element handle
  • out_ctx: content of output stream.

esp_err_t downmix_set_source_stream_info(audio_element_handle_t self, int rate, int ch, int index)

Sets the sample rate and the number of channels of input stream to be processed.

Return
ESP_OK ESP_FAIL
Parameters
  • self: audio element handle
  • rate: sample rate of the input stream
  • ch: number of channel(s) of the input stream
  • index: The index of input stream. The index must be in [0, SOURCE_NUM_MAX - 1] range.

esp_err_t downmix_set_gain_info(audio_element_handle_t self, float *gain, int index)

Sets the audio gain to be processed.

Return
ESP_OK ESP_FAIL
Parameters
  • self: audio element handle
  • gain: the reset value of gain. The gain is an array of two elements.
  • index: The index of input stream. The index must be in [0, SOURCE_NUM_MAX - 1] range.

esp_err_t downmix_set_transit_time_info(audio_element_handle_t self, int transit_time, int index)

Sets the audio transit_time to be processed.

Return
ESP_OK ESP_FAIL
Parameters
  • self: audio element handle
  • transit_time: the reset value of transit_time
  • index: The index of input stream. The index must be in [0, SOURCE_NUM_MAX - 1] range

esp_err_t source_info_init(audio_element_handle_t self, esp_downmix_input_info_t *source_num)

Initializes information of the source streams for downmixing.

Return
ESP_OK ESP_FAIL
Parameters
  • self: audio element handle
  • source_num: The information array of source streams

audio_element_handle_t downmix_init(downmix_cfg_t *config)

Initializes the Audio Element handle for downmixing.

Return
The initialized Audio Element handle
Parameters
  • config: the configuration

Structures

struct downmix_cfg_t

Downmix configuration.

Public Members

esp_downmix_info_t downmix_info

Downmix information

int max_sample

The number of samples per downmix processing

int out_rb_size

Size of ring buffer

int task_stack

Size of task stack

int task_core

Task running in core…

int task_prio

Task priority (based on the FreeRTOS priority)

bool stack_in_ext

Try to allocate stack in external memory

Macros

DOWNMIX_TASK_STACK
DOWNMIX_TASK_CORE
DOWNMIX_TASK_PRIO
DOWNMIX_RINGBUFFER_SIZE
DM_BUF_SIZE
DEFAULT_DOWNMIX_CONFIG()