A2DPEncoder Class Reference

Base class for a single A2DP codec's encode support: pairs an A2DP codec type and its SEP capability advertisement with an audio_tools::AudioEncoder that performs the actual encoding. Provide one concrete subclass per codec (see A2DPEncoderSBC, A2DPEncoderAAC) and register instances via BluetoothA2DPSource::add_encoder() - stream endpoint registration is driven entirely by what gets registered here. More...

#include <A2DPEncoder.h>

Inheritance diagram for A2DPEncoder:

Classes
class	FrameOutput
	Forwards the encoder output to write_encoded() More...

Public Member Functions
	A2DPEncoder (audio_tools::AudioEncoder &encoder)
virtual bool	begin (const esp_a2d_mcc_t &mcc)
virtual void	build_capability (esp_a2d_mcc_t &mcc)=0
	Fills in the SEP capability advertised for this codec at registration.
virtual esp_a2d_mct_t	codec_type ()=0
	A2DP codec type this encoder handles (e.g. ESP_A2D_MCT_SBC)
virtual void	end ()
	Closes the wrapped audio_tools encoder.
audio_tools::AudioInfo	get_audio_info ()
	Negotiated sample rate/channels (the PCM is always provided as stereo)
virtual int	max_frames_per_packet ()
	Max number of encoded frames that can be combined in one media packet.
virtual const char *	mime ()=0
	MIME type of the codec this encoder produces (e.g. "audio/sbc")
virtual uint16_t	payload_header_size ()
int	sample_rate ()
	Sample rate of the PCM provided by the data callbacks.
virtual uint32_t	samples_per_frame ()=0
void	set_frame_sink (A2DPFrameSink *sink)
	Defines the target of the encoded frames.
void	set_sample_rate (int rate)
virtual size_t	write (const uint8_t *pcm, size_t len)

Protected Member Functions
virtual void	configure (const esp_a2d_mcc_t &mcc)
	optional codec specific configuration of the wrapped encoder
virtual void	parse_audio_info (const esp_a2d_mcc_t &mcc)=0
virtual void	write_encoded (const uint8_t *data, size_t len)

Protected Attributes
int	channels_cfg = 2
FrameOutput	frame_output
int	input_sample_rate = 44100
audio_tools::AudioEncoder *	p_encoder
A2DPFrameSink *	p_sink = nullptr
int	sample_rate_cfg = 44100

Detailed Description

Base class for a single A2DP codec's encode support: pairs an A2DP codec type and its SEP capability advertisement with an audio_tools::AudioEncoder that performs the actual encoding. Provide one concrete subclass per codec (see A2DPEncoderSBC, A2DPEncoderAAC) and register instances via BluetoothA2DPSource::add_encoder() - stream endpoint registration is driven entirely by what gets registered here.

The PCM which is provided by the data callbacks of the source is always 16 bit stereo (as in the legacy source API) at the sample rate defined with set_sample_rate() (default 44100). The sample rate is the only one advertised to the sink. If the sink negotiates mono, the PCM is downmixed before it is encoded.

Author

Phil Schatzmann

Copyright

Apache License Version 2

Member Function Documentation

begin()

virtual bool A2DPEncoder::begin ( const esp_a2d_mcc_t &  mcc )

inlinevirtual

Opens the wrapped audio_tools encoder for the negotiated SEP configuration: calls parse_audio_info(mcc) and configure(mcc) (implemented per codec), then wires up the frame output and starts the encoder.

Reimplemented in A2DPEncoderAAC.

build_capability()

virtual void A2DPEncoder::build_capability ( esp_a2d_mcc_t &  mcc )

pure virtual

Fills in the SEP capability advertised for this codec at registration.

Implemented in A2DPEncoderAAC, and A2DPEncoderSBC.

codec_type()

virtual esp_a2d_mct_t A2DPEncoder::codec_type ( )

pure virtual

A2DP codec type this encoder handles (e.g. ESP_A2D_MCT_SBC)

Implemented in A2DPEncoderAAC, and A2DPEncoderSBC.

configure()

virtual void A2DPEncoder::configure ( const esp_a2d_mcc_t &  mcc )

inlineprotectedvirtual

optional codec specific configuration of the wrapped encoder

Reimplemented in A2DPEncoderAAC, and A2DPEncoderSBC.

max_frames_per_packet()

virtual int A2DPEncoder::max_frames_per_packet ( )

inlinevirtual

Max number of encoded frames that can be combined in one media packet.

Reimplemented in A2DPEncoderSBC.

mime()

virtual const char * A2DPEncoder::mime ( )

pure virtual

MIME type of the codec this encoder produces (e.g. "audio/sbc")

Implemented in A2DPEncoderAAC, and A2DPEncoderSBC.

parse_audio_info()

virtual void A2DPEncoder::parse_audio_info ( const esp_a2d_mcc_t &  mcc )

protectedpure virtual

determines sample_rate_cfg/channels_cfg from the negotiated configuration

Implemented in A2DPEncoderAAC, and A2DPEncoderSBC.

payload_header_size()

virtual uint16_t A2DPEncoder::payload_header_size ( )

inlinevirtual

Bytes of the audio MTU that are needed by the media payload header which is added by the stack (e.g. SBC: 1 byte, AAC: LATM header)

Reimplemented in A2DPEncoderSBC.

samples_per_frame()

virtual uint32_t A2DPEncoder::samples_per_frame ( )

pure virtual

Number of samples (per channel) covered by one encoded frame: used for the media packet timestamps

Implemented in A2DPEncoderAAC, and A2DPEncoderSBC.

set_sample_rate()

void A2DPEncoder::set_sample_rate ( int  rate )

inline

Defines the sample rate of the PCM provided by the data callbacks (default 44100). Call before BluetoothA2DPSource::start().

write()

virtual size_t A2DPEncoder::write ( const uint8_t *  pcm, size_t  len  )

inlinevirtual

Feeds 16 bit stereo PCM to the wrapped encoder (downmixed to mono if this was negotiated); the encoded frames are forwarded to the frame sink

write_encoded()

virtual void A2DPEncoder::write_encoded ( const uint8_t *  data, size_t  len  )

inlineprotectedvirtual

Receives the output of the wrapped encoder: by default each write is expected to be exactly one encoded frame

Reimplemented in A2DPEncoderAAC.

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The documentation for this class was generated from the following file:

• src/A2DPEncoder.h