Configure the audio codec

In audio streaming, the choice of an encoding algorithm affects both quality and bit rate. Your goal is to lower the required bit rate while maintaining quality at the desired level. This page shows you how to configure the audio codec IoT SDK uses to stream media in your app.

Prerequisites

In order to follow this procedure you must have:

• Implemented the basic IoT SDK functionality. See Build from scratch.

Understand the tech

IoT SDK offers the following built-in audio codecs:

• AUDIO_CODEC_TYPE_OPUS
• AUDIO_CODEC_TYPE_G722
• AUDIO_CODEC_TYPE_G711A
• AUDIO_CODEC_TYPE_G711U

Specify an audio codec when you join a channel. Set the sampling rate and the number of channels based on your audio quality requirements. If your app needs a custom encoding algorithm, disable use of a built-in codec and implement your own encoder.

Starting with v1.9.7, IoT SDK also supports 8 kHz AAC-LC audio. Configure the audio packet duration using pcm_duration.

Send audio data

Use a built-in codec

Set the audio codec, sampling rate, and the number of channels in channel_options that you pass to agora_rtc_join_channel. To set these parameters, use the config object or modify the following lines in main():

channel_options.audio_codec_opt.audio_codec_type = config->audio_codec_type;
channel_options.audio_codec_opt.pcm_sample_rate = config->pcm_sample_rate;
channel_options.audio_codec_opt.pcm_channel_num = config->pcm_channel_num;

When you call agora_rtc_send_audio_data to send audio, set data_type to AUDIO_DATA_TYPE_PCM:

audio_frame_info_t info = { 0 };
info.data_type = AUDIO_DATA_TYPE_PCM;
int rval = agora_rtc_send_audio_data(g_conn_id, data, len, &info);
if (rval < 0) {
    printf("Failed to send audio data, reason: %s\n", agora_rtc_err_2_str(rval));
    return -1;
}

Use your own codec

To use your own audio codec, set channel_options.audio_codec_opt.audio_codec_type to AUDIO_CODEC_DISABLED. When you call agora_rtc_send_audio_data, set the data_type parameter of audio_frame_info to your encoding format. This setting transmits the audio encoding format as is to the receiving end. When you disable use of a built-in audio codec, IoT SDK does not process the audio.

Receive audio data

With a built-in codec, IoT SDK automatically decodes incoming audio. Use the on_audio_data callback you registered in Listen for events to receive it; its info_ptr->data_type field is AUDIO_DATA_TYPE_PCM.

With your own codec, the receiving end obtains the encoded audio data and the encoding format through the same on_audio_data callback, and decodes it using a custom decoder.

Reference

This section contains content that completes the information on this page, or points you to documentation that explains other aspects of this product.

API reference

• enum audio_codec_type_e