Prosody RTP processing: API: sm_vmptx_config_codec_evrc

Prototype Definition

int sm_vmptx_config_codec_evrc(struct sm_vmptx_codec_evrc_parms *codecp)

Parameters

a structure of the following type:

typedef struct sm_vmptx_codec_evrc_parms {
	tSMVMPtxId vmptx;					/* in */
	tSM_INT payload_type;					/* in */
	tSM_INT high_pass_filter;				/* in */
	tSM_INT noise_suppression_filter;			/* in */
	enum kSMEVRCRTPMode rtp_mode;				/* in */
	enum kSMEVRCRate {
		kSMEVRCRateEighth,
		kSMEVRCRateHalf,
		kSMEVRCRateFull,
	} max_rate;						/* in */
	enum kSMEVRCRate min_rate;				/* in */
	enum kSMVMPTxVADMode VADMode;				/* in */
	tSM_INT frames_per_packet;				/* in */
} SM_VMPTX_CODEC_EVRC_PARMS;

Description

Configures a VMP[tx] to use the Enhanced Variable Rate Codec (EVRC) for encoding data.

This requires the module evrc to have been downloaded.

Fields

vmptx

The VMP[tx] to which to add this codec

payload_type

The payload type identifer to use with this codec (see IETF RFC 3550 section 13). Supplying a value of -1 will remove any payload type configuration from the codec preventing its use.

high_pass_filter

Selects whether or not a high-pass filter is used on the data to be encoded. The filter is used if this value is non-zero.

noise_suppression_filter

Selects whether or not a noise suppression filter is used on the data to be encoded. The filter is used if this value is non-zero.

rtp_mode

Selects the RTP format for this codec. There are two commonly-used specifications for how to pack the the encoded data into an RTP packet. One of these values:

kSMEVRCRTPModeHeaderless: Encodes the bitstream as raw encoded bytes, with no headers. This requires that there is only one frame per packet.
kSMEVRCRTPModeRFC2658: Encodes the bitstream as specified in IETF RFC 2658. The header is one byte. This specification only allows for one frame per packet.
kSMEVRCRTPModeRFC3558: Encodes the bitstream as specified in IETF RFC 3558. The header is two bytes, plus one byte for every two frames in the packet.

max_rate

The maximum encoding rate to use. All frames are guaranteed to be this size or smaller. One of these values:

kSMEVRCRateEighth: Eighth rate: 16 bits per frame. This rate is only used for comfort noise frames.
kSMEVRCRateHalf: Half rate: 80 bits per frame.
kSMEVRCRateFull: Full rate: 171 bits per frame.

min_rate

The minimum encoding rate to use. All frames are guaranteed to be at least this size, or be elided if VAD is enabled. One of these values:

kSMEVRCRateEighth: Eighth rate: 16 bits per frame. This rate is only used for comfort noise frames.
kSMEVRCRateHalf: Half rate: 80 bits per frame.
kSMEVRCRateFull: Full rate: 171 bits per frame.

VADMode

The mode of operation for the voice activity detector One of these values:

kSMVMPTxVADModeDisabled: Disable VAD - all data delivered to the VMP[tx] is encoded and sent
kSMVMPTxVADModeEnabled: Enable VAD - if the signal is inactive, no data is sent (DTX)
kSMVMPTxVADModeComfortNoise: Enable VAD with comfort noise generation - if the signal is inactive, comfort noise packets are sent. If the main codec does not define its own comfort noise, it must have been configured by sm_vmptx_config_codec_comfort_noise().

frames_per_packet

The number of frames to send per packet. This value is normally one, which encodes 20 milliseconds per packet, but larger values can be used, reducing the packet overhead at the expense of extra delay. This field must be set to one unless rtp_mode is kSMEVRCRTPModeRFC3558.

Returns

0 if call completed successfully, otherwise a standard error such as:

ERR_SM_DEVERR - device error

This function is part of the Prosody RTP processing API.