Ogg Demo#

Overview#

This sample demonstrates a real-time Opus-based audio loopback flow on K230, with Ogg muxing and demuxing inserted in the middle of the pipeline. The program captures audio from AI, encodes it with AENC as Opus, performs Ogg mux and demux entirely in memory, then sends the decoded stream to ADEC and finally plays it through AO.

Ogg muxing: package Opus frames output by AENC into Ogg pages
Ogg demuxing: extract Opus frames from Ogg pages
Real-time loopback: AI -> AENC -> Ogg mux -> Ogg demux -> ADEC -> AO
Exit method: the program keeps running until Ctrl+C, then triggers signal handling and resource cleanup

Usage#

Code Location#

Sample directory:

/src/rtsmart/examples/mpp/sample_ogg

The current entry file is main.cpp, and the built executable is sample_ogg.elf.

Key Parameters#

Parameter	Description	Value
`SAMPLE_RATE`	audio sample rate	`16000 Hz`
`AUDIO_PERSEC_DIV_NUM`	audio frames per second	`25`
`MAX_AUDIO_STREAM_SIZE`	intermediate Ogg/Opus buffer size	`1000 bytes`
codec format	payload type used by `AENC` and `ADEC`	`Opus`
codec channel count	encode and decode channels	`1`
sample precision	I2S bit width	`16 bit`
AI/AO device ID	default device used by the program	`0`
AI/AO/AENC/ADEC channel ID	default channel used by the program	`0`

Run Program#

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

./sample_ogg.elf

At startup, the program prints messages similar to:

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

Code Flow Description#

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 the intermediate audio stream used as ADEC input. The sample uses kd_mpi_vb_get_block(), kd_mpi_vb_handle_to_phyaddr(), and kd_mpi_sys_mmap() to map the physical buffer into user space.
Initialize the Ogg components init_ogg_muxer() configures kd_ogg_muxer_params with 16 kHz, mono, and streaming output mode. init_ogg_demuxer() creates the Ogg demuxer used to restore Ogg pages back into Opus frames.
Configure audio input, output, and codecs In audio_sample_ogg(), both AI and AO are configured in I2S mode with the built-in codec. AI and AO both use 16 bit, 16 kHz, and AUDIO_PERSEC_DIV_NUM = 25. The sample creates AENC and ADEC channels with payload type K_PT_OPUS.
Build the MPP binding relationships kd_mpi_sys_bind() binds the AI channel to AENC. kd_mpi_sys_bind() binds the ADEC channel to AO.
Perform Ogg muxing and demuxing in memory The main loop gets the encoded Opus stream through kd_mpi_aenc_get_stream(). do_opus_stream() first calls kd_ogg_write_frame_ex() to package the Opus frame into an Ogg page. It then calls kd_ogg_demuxer_feed_page_ex() to extract the Opus frame back from that page. The extracted Opus data is copied into the preallocated g_audio_stream buffer and sent to the decoder through kd_mpi_adec_send_stream(). After processing, the sample calls kd_mpi_aenc_release_stream() to release the encoded stream.
Exit on signal and clean up resources main() registers SIGINT and SIGTERM. Once a signal is received, g_running is set to false. After the loop exits, the program unbinds AI/AENC and ADEC/AO, then closes AI, AO, AENC, and ADEC. cleanup_resources() destroys the Ogg muxer and demuxer, releases the VB block, destroys the VB pool, and calls kd_mpi_vb_exit().

Notes#

This sample does not read or write .ogg files. All Ogg muxing and demuxing are performed in memory.
The sample uses device ID 0 and channel ID 0 by default. If you port it to a different audio path, update the code accordingly.
If audio-device initialization fails, the program prints an error and immediately enters the cleanup path.

Tip

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