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CM AAC Encode

CM AAC Encode

Owned by wang.zhou
May 20, 2024
2 min read

The cmAacEncode is used to encode the audio/x-raw(PCM) data to audio/mpeg(AAC) data by the library fdkaac.

API Instructions

create/destroy

gpointer cm_aac_encode_create(); void cm_aac_encode_destroy(gpointer hd);

start/stop

void cm_aac_encode_start(gpointer hd); void cm_aac_encode_stop(gpointer hd);

parameters

/* @format Aac encode format, supports adts, adif, raw */ void cm_aac_encode_set_stream_format(gpointer hd, const char* format); /* @br The aac bitrate */ void cm_aac_encode_set_bitrate(gpointer hd, int br); /* @return Encode output format, "audio/mpeg,..." */ const char* cm_aac_encode_get_caps_str(gpointer hd);

data

The encoder needs to know the actual format of the input before encoding, so must ensure the source is ready to be linked(the media info is ready).

/* @src An audio/x-raw source(cmAlsaSrc, ...) */ void cm_aac_encode_link_to_source(gpointer hd, gpointer src); void cm_aac_encode_unlink(gpointer hd); /* @ cb data callback to get data */ void cm_aac_encode_set_data_callback(gpointerhd, cm_data_cb_ptrcb, gpointeruser_data); void cm_aac_encode_remove_data_callback(gpointerhd, cm_data_cb_ptrcb, gpointeruser_data);

others

GstElement* cm_aac_encode_get_bin(gpointer hd);

Demo

Aac Encode Demo

Structure

Get raw data from the microphone then encode it to AAC.

image-20240520-071617.png

Main codes

// The data will be send to here static GstFlowReturn _out_data_cb (GstBuffer *buffer, gpointer user_data) { ...... return GST_FLOW_OK; } static gboolean _main_loop(gpointer arg) { if(!pcm_hd) { // Create source and start pcm_hd = cm_audio_alsa_source_create("hw:0,0"); cm_audio_alsa_source_start(pcm_hd); } //Wait alsa source is ready to be linked if(!aac_hd && cm_audio_alsa_source_is_ready(pcm_hd)){ aac_hd = cm_aac_encode_create(); //Link aac encode to alsa source cm_aac_encode_link_to_source(aac_hd, pcm_hd); //Set callback to get aac data cm_aac_encode_start(aac_hd); } ...... }

For more details please refer to the demo file.
Test result

image-20240520-071703.png

The AAC data can be saved to the file and displayed on the PC.

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