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Ogg Demo

Introduction

This example demonstrates the real-time audio loopback processing flow based on Opus on K230, with Ogg encapsulation and decapsulation steps inserted in the middle. The program collects audio from AI, hands it to AENC for Opus encoding, then completes Ogg mux/demux in memory, and finally sends it to ADEC for decoding and plays it through AO.

• Ogg encapsulation: Pack Opus frames output by AENC into Ogg pages

• Ogg decapsulation: Extract Opus frames from Ogg pages

• Real-time loopback: AI -> AENC -> Ogg mux -> Ogg demux -> ADEC -> AO

• Exit method: The program runs continuously; press Ctrl+C to trigger signal handling and clean up resources

Usage Instructions

Code Location

Example directory: /src/rtsmart/examples/mpp/sample_ogg

The current example entry file is main.cpp, which generates the executable sample_ogg.elf after building.

Key Parameters

Parameter Name	Description	Value
SAMPLE_RATE	Audio sampling rate	16000 Hz
AUDIO_PERSEC_DIV_NUM	Number of audio frames per second	25
MAX_AUDIO_STREAM_SIZE	Ogg/Opus intermediate buffer size	1000 bytes
Encoding format	Payload type used by AENC/ADEC	Opus
Encoding channel count	Codec channel count	1
Sampling precision	I2S bit width	16 bit
AI/AO device number	Used by the program by default	0
AI/AO/AENC/ADEC channel number	Used by the program by default	0

Running the Program

After startup, the program initializes VB, AI, AO, AENC, ADEC, Ogg muxer, and demuxer, then enters the loop to process real-time audio. Press Ctrl+C to exit.

./sample_ogg.elf

The example prints messages similar to the following at startup:

Starting Ogg audio sample program. Press Ctrl+C to exit.
vb_set_config succeeded
Ogg stream muxer initialized successfully.

Code Flow Description

1. Initialize VB resources

   • audio_sample_vb_init() calls kd_mpi_vb_set_config() and kd_mpi_vb_init() to initialize the VB system.

   • audio_data_vb_create_pool() creates a private VB pool for saving the intermediate audio stream used as ADEC input.

   • Use kd_mpi_vb_get_block(), kd_mpi_vb_handle_to_phyaddr(), and kd_mpi_sys_mmap() to establish mapping from physical address to user space.

2. Initialize Ogg components

   • init_ogg_muxer() configures kd_ogg_muxer_params, setting sampling rate to 16 kHz, mono channel, and streaming output.

   • init_ogg_demuxer() creates the Ogg demuxer, used to restore pages back to Opus frames.

3. Configure audio input, output, and codecs

   • In audio_sample_ogg(), both AI and AO are configured to I2S mode of the built-in codec.

   • Both AI/AO are set to 16 bit, 16 kHz, AUDIO_PERSEC_DIV_NUM=25.

   • Create AENC/ADEC channels with payload type K_PT_OPUS.

4. Establish MPP binding relationships

   • kd_mpi_sys_bind() binds the AI channel to AENC.

   • kd_mpi_sys_bind() binds the ADEC channel to AO.

5. Perform Ogg encapsulation and decapsulation in memory

   • The main loop obtains the Opus encoded stream through kd_mpi_aenc_get_stream().

   • do_opus_stream() first calls kd_ogg_write_frame_ex() to encapsulate Opus frames into Ogg pages.

   • Then it calls kd_ogg_demuxer_feed_page_ex() to extract Opus frames from the pages.

   • The extracted Opus data is copied to the pre-allocated g_audio_stream buffer, and then sent to the decoder through kd_mpi_adec_send_stream().

   • After processing, kd_mpi_aenc_release_stream() is called to release the encoded stream.

6. Signal exit and resource cleanup

   • main() registers SIGINT and SIGTERM; upon receiving a signal, it sets g_running to false.

   • After the loop exits, the program unbinds AI/AENC and ADEC/AO, and closes AI, AO, AENC, ADEC.

   • cleanup_resources() destroys the Ogg muxer and demuxer, releases VB blocks, destroys the VB pool, and calls kd_mpi_vb_exit().

Notes

• This example does not read or write .ogg files; Ogg encapsulation and decapsulation are all completed in memory.

• The example fixedly uses device number 0 and channel number 0; adjustments to the code are required when porting to other audio chains.

• If audio device initialization fails, the program will directly print the error and execute the cleanup flow.

Tip

For interfaces related to Ogg processing and audio codecs, please read together with sample_ogg/main.cpp and the corresponding audio API documentation.