Codec Framework

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Detailed Description

Codec Management

Codec Manager

The codec manager is used to manage all codec capabilities in the endpoint. When used with media endpoint (pjmedia_endpt), application can retrieve the codec manager instance by calling pjmedia_endpt_get_codec_mgr().

Registering New Codec

New codec types can be registered to PJMEDIA (or to be precise, to the codec manager) during run-time. To do this, application needs to initialize an instance of codec factory (pjmedia_codec_factory) and registers this codec factory by calling pjmedia_codec_mgr_register_factory().

For codecs implemented/supported by PJMEDIA, this process is normally concealed in an easy to use function such as pjmedia_codec_g711_init().

Codec Factory

A codec factory (pjmedia_codec_factory) is registered to codec manager, and it is used to create and release codec instance.

The most important member of the codec factory is the "virtual" function table pjmedia_codec_factory_op, where it contains, among other thing, pointer to functions to allocate and deallocate codec instance.

Codec Instance

Application allocates codec instance by calling pjmedia_codec_mgr_alloc_codec(). One codec instance (pjmedia_codec) can be used for simultaneous encoding and decoding.

The most important member of the codec instance is the "virtual" function table pjmedia_codec_op, where it holds pointer to functions to encode/decode media frames.

Codec Identification

A particular codec type in PJMEDIA can be uniquely identified by two keys: by pjmedia_codec_info, or by pjmedia_codec_id string. A fully qualified codec ID string consists of codec name, sampling rate, and number of channels. However, application may use only first parts of the tokens as long as it will make to codec ID unique. For example, "gsm" is a fully qualified codec name, since it will always have 8000 clock rate and 1 channel. Other examples of fully qualified codec ID strings are "pcma", "speex/8000", "speex/16000", and "L16/16000/1". A codec id "speex" (without clock rate) is not fully qualified, since it will match the narrowband, wideband, and ultrawideband Speex codec.

The two keys can be converted to one another, with pjmedia_codec_info_to_id() and pjmedia_codec_mgr_find_codecs_by_id() functions.

Codec ID string is not case sensitive.

Using the Codec Framework

Allocating Codec

Application needs to allocate one codec instance for encoding and decoding media frames. One codec instance can be used to perform both encoding and decoding.

Application allocates codec by calling pjmedia_codec_mgr_alloc_codec(). This function takes pjmedia_codec_info argument, which is used to locate the particular codec factory to be used to allocate the codec.

Application can build pjmedia_codec_info structure manually for the specific codec, or alternatively it may get the pjmedia_codec_info from the codec ID string, by using pjmedia_codec_mgr_find_codecs_by_id() function.

The following snippet shows an example to allocate a codec:

    pj_str_t codec_id;
    pjmedia_codec_info *codec_info;
    unsigned count = 1;
    pjmedia_codec *codec;

    codec_id = pj_str("pcma");

    // Find codec info for the specified coded ID (i.e. "pcma").
    status = pjmedia_codec_mgr_find_codecs_by_id( codec_mgr, &codec_id,
                                                  &count, &codec_info, NULL);

    // Allocate the codec.
    status = pjmedia_codec_mgr_alloc_codec( codec_mgr, codec_info, &codec );

Initializing Codec

Once codec is allocated, application needs to initialize the codec by calling open member of the codec. This function takes pjmedia_codec_param as the argument, which contains the settings for the codec.

Application shoud use pjmedia_codec_mgr_get_default_param() function to initiaize pjmedia_codec_param. The setting part of pjmedia_codec_param then can be tuned to suit the application's requirements.

The following snippet shows an example to initialize codec:

    pjmedia_codec_param param;

    // Retrieve default codec param for the specified codec.
    pjmedia_codec_mgr_get_default_param(codec_mgr, codec_info
                                        &param);

    // Application may change the "settings" part of codec param,
    // for example, to disable VAD
    param.setting.vad = 0;

    // Open the codec using the specified settings.
    codec->op->open( codec, &param );

Encoding and Decoding Media Frames

Application encodes and decodes media frames by calling encode and decode member of the codec's "virtual" function table (pjmedia_codec_op).

Concealing Lost Frames

All codecs has Packet Lost Concealment (PLC) feature, and application can activate the PLC to conceal lost frames by calling recover member of the codec's "virtual" function table (pjmedia_codec_op).

If the codec's algorithm supports PLC, the recover function will use the codec's PLC. Otherwise for codecs that don't have intrinsic PLC, PJMEDIA will suply the PLC implementation from the Packet Lost Concealment (PLC) implementation.

Closing and Releasing the Codec

The codec must be closed by calling close member of the codec's operation. Then it must be released by calling pjmedia_codec_mgr_dealloc_codec().

Table of Contents
	G711
	Standard G.711/PCMA and PCMU codec. This section describes functions to register and register G.711 codec factory to the codec manager. After the codec factory has been registered, application can use Codec Framework API to manipulate the codec.
	G.722 Codec
	Implementation of G.722 Codec.
	GSM 06.10 Codec
	Implementation of GSM FR based on GSM 06.10 library.
	iLBC Codec
	Implementation of iLBC Codec.
	L16 Codec Family
	PCM/16bit/linear codecs.
	Speex Codec Family
	Implementation of Speex codecs (narrow/wide/ultrawide-band).
Data Structures
struct	pjmedia_codec_info
struct	pjmedia_codec_param
struct	pjmedia_codec_op
struct	pjmedia_codec
struct	pjmedia_codec_factory_op
struct	pjmedia_codec_factory
struct	pjmedia_codec_desc
struct	pjmedia_codec_mgr
Defines
#define	PJMEDIA_CODEC_MGR_MAX_CODECS   32
Typedefs
typedef struct pjmedia_codec	pjmedia_codec
typedef struct pjmedia_codec_factory	pjmedia_codec_factory
typedef char	pjmedia_codec_id [32]
Enumerations
enum	pjmedia_rtp_pt {   PJMEDIA_RTP_PT_PCMU = 0,   PJMEDIA_RTP_PT_GSM = 3,   PJMEDIA_RTP_PT_G723 = 4,   PJMEDIA_RTP_PT_DVI4_8K = 5,   PJMEDIA_RTP_PT_DVI4_16K = 6,   PJMEDIA_RTP_PT_LPC = 7,   PJMEDIA_RTP_PT_PCMA = 8,   PJMEDIA_RTP_PT_G722 = 9,   PJMEDIA_RTP_PT_L16_2 = 10,   PJMEDIA_RTP_PT_L16_1 = 11,   PJMEDIA_RTP_PT_QCELP = 12,   PJMEDIA_RTP_PT_CN = 13,   PJMEDIA_RTP_PT_MPA = 14,   PJMEDIA_RTP_PT_G728 = 15,   PJMEDIA_RTP_PT_DVI4_11K = 16,   PJMEDIA_RTP_PT_DVI4_22K = 17,   PJMEDIA_RTP_PT_G729 = 18,   PJMEDIA_RTP_PT_CELB = 25,   PJMEDIA_RTP_PT_JPEG = 26,   PJMEDIA_RTP_PT_NV = 28,   PJMEDIA_RTP_PT_H261 = 31,   PJMEDIA_RTP_PT_MPV = 32,   PJMEDIA_RTP_PT_MP2T = 33,   PJMEDIA_RTP_PT_H263 = 34,   PJMEDIA_RTP_PT_DYNAMIC = 96 }
enum	pjmedia_codec_priority {   PJMEDIA_CODEC_PRIO_HIGHEST = 255,   PJMEDIA_CODEC_PRIO_NEXT_HIGHER = 254,   PJMEDIA_CODEC_PRIO_NORMAL = 128,   PJMEDIA_CODEC_PRIO_LOWEST = 1,   PJMEDIA_CODEC_PRIO_DISABLED = 0 }
Functions
pj_status_t	pjmedia_codec_mgr_init (pjmedia_codec_mgr *mgr)
pj_status_t	pjmedia_codec_mgr_register_factory (pjmedia_codec_mgr *mgr, pjmedia_codec_factory *factory)
pj_status_t	pjmedia_codec_mgr_unregister_factory (pjmedia_codec_mgr *mgr, pjmedia_codec_factory *factory)
pj_status_t	pjmedia_codec_mgr_enum_codecs (pjmedia_codec_mgr *mgr, unsigned *count, pjmedia_codec_info info[], unsigned *prio)
pj_status_t	pjmedia_codec_mgr_get_codec_info (pjmedia_codec_mgr *mgr, unsigned pt, const pjmedia_codec_info **inf)
char *	pjmedia_codec_info_to_id (const pjmedia_codec_info *info, char *id, unsigned max_len)
pj_status_t	pjmedia_codec_mgr_find_codecs_by_id (pjmedia_codec_mgr *mgr, const pj_str_t *codec_id, unsigned *count, const pjmedia_codec_info *p_info[], unsigned prio[])
pj_status_t	pjmedia_codec_mgr_set_codec_priority (pjmedia_codec_mgr *mgr, const pj_str_t *codec_id, pj_uint8_t prio)
pj_status_t	pjmedia_codec_mgr_get_default_param (pjmedia_codec_mgr *mgr, const pjmedia_codec_info *info, pjmedia_codec_param *param)
pj_status_t	pjmedia_codec_mgr_alloc_codec (pjmedia_codec_mgr *mgr, const pjmedia_codec_info *info, pjmedia_codec **p_codec)
pj_status_t	pjmedia_codec_mgr_dealloc_codec (pjmedia_codec_mgr *mgr, pjmedia_codec *codec)

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Define Documentation

#define PJMEDIA_CODEC_MGR_MAX_CODECS   32

Declare maximum codecs

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Typedef Documentation

typedef char pjmedia_codec_id[32]

Codec identification (e.g. "pcmu/8000/1"). See Codec Identification for more info.

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Enumeration Type Documentation

enum pjmedia_rtp_pt

Standard RTP static payload types, as defined by RFC 3551. The header file <pjmedia-codec/types.h> also declares dynamic payload type numbers that are used by PJMEDIA when advertising the capability for example in SDP message.

Enumerator:

PJMEDIA_RTP_PT_PCMU	audio PCMU
PJMEDIA_RTP_PT_GSM	audio GSM
PJMEDIA_RTP_PT_G723	audio G723
PJMEDIA_RTP_PT_DVI4_8K	audio DVI4 8KHz
PJMEDIA_RTP_PT_DVI4_16K	audio DVI4 16Khz
PJMEDIA_RTP_PT_LPC	audio LPC
PJMEDIA_RTP_PT_PCMA	audio PCMA
PJMEDIA_RTP_PT_G722	audio G722
PJMEDIA_RTP_PT_L16_2	audio 16bit linear 44.1KHz stereo
PJMEDIA_RTP_PT_L16_1	audio 16bit linear 44.1KHz mono
PJMEDIA_RTP_PT_QCELP	audio QCELP
PJMEDIA_RTP_PT_CN	audio Comfort Noise
PJMEDIA_RTP_PT_MPA	audio MPEG1/MPEG2 elemetr. streams
PJMEDIA_RTP_PT_G728	audio G728
PJMEDIA_RTP_PT_DVI4_11K	audio DVI4 11.025KHz mono
PJMEDIA_RTP_PT_DVI4_22K	audio DVI4 22.050KHz mono
PJMEDIA_RTP_PT_G729	audio G729
PJMEDIA_RTP_PT_CELB	video/comb Cell-B by Sun (RFC2029)
PJMEDIA_RTP_PT_JPEG	video JPEG
PJMEDIA_RTP_PT_NV	video NV by nv program by Xerox
PJMEDIA_RTP_PT_H261	video H261
PJMEDIA_RTP_PT_MPV	video MPEG1 or MPEG2 elementary
PJMEDIA_RTP_PT_MP2T	video MPEG2 transport
PJMEDIA_RTP_PT_H263	video H263
PJMEDIA_RTP_PT_DYNAMIC	start of dynamic RTP payload

enum pjmedia_codec_priority

Specify these values to set the codec priority, by calling pjmedia_codec_mgr_set_codec_priority().

Enumerator:

PJMEDIA_CODEC_PRIO_HIGHEST	This priority makes the codec the highest in the order. The last codec specified with this priority will get the highest place in the order, and will change the priority of previously highest priority codec to NEXT_HIGHER.
PJMEDIA_CODEC_PRIO_NEXT_HIGHER	This priority will put the codec as the next codec after codecs with this same priority.
PJMEDIA_CODEC_PRIO_NORMAL	This is the initial codec priority when it is registered to codec manager by codec factory.
PJMEDIA_CODEC_PRIO_LOWEST	This priority makes the codec the lowest in the order. The last codec specified with this priority will be put in the last place in the order.
PJMEDIA_CODEC_PRIO_DISABLED	This priority will prevent the codec from being listed in the SDP created by media endpoint, thus should prevent the codec from being used in the sessions. However, the codec will still be listed by pjmedia_codec_mgr_enum_codecs() and other codec query functions.

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Function Documentation

pj_status_t pjmedia_codec_mgr_init

(

pjmedia_codec_mgr *

mgr

)

Initialize codec manager. Normally this function is called by pjmedia endpoint's initialization code.

Parameters:

mgr

Codec manager instance.

Returns:

PJ_SUCCESS on success.

pj_status_t pjmedia_codec_mgr_register_factory	(	pjmedia_codec_mgr *	mgr,
		pjmedia_codec_factory *	factory
	)

Register codec factory to codec manager. This will also register all supported codecs in the factory to the codec manager.

Parameters:

	mgr	The codec manager instance. Application can get the instance by calling pjmedia_endpt_get_codec_mgr().
	factory	The codec factory to be registered.

Returns:

PJ_SUCCESS on success.

pj_status_t pjmedia_codec_mgr_unregister_factory	(	pjmedia_codec_mgr *	mgr,
		pjmedia_codec_factory *	factory
	)

Unregister codec factory from the codec manager. This will also remove all the codecs registered by the codec factory from the codec manager's list of supported codecs.

Parameters:

	mgr	The codec manager instance. Application can get the instance by calling pjmedia_endpt_get_codec_mgr().
	factory	The codec factory to be unregistered.

Returns:

PJ_SUCCESS on success.

pj_status_t pjmedia_codec_mgr_enum_codecs	(	pjmedia_codec_mgr *	mgr,
		unsigned *	count,
		pjmedia_codec_info	info[],
		unsigned *	prio
	)

Enumerate all supported codecs that have been registered to the codec manager by codec factories.

Parameters:

	mgr	The codec manager instance. Application can get the instance by calling pjmedia_endpt_get_codec_mgr().
	count	On input, specifies the number of elements in the array. On output, the value will be set to the number of elements that have been initialized by this function.
	info	The codec info array, which contents will be initialized upon return.
	prio	Optional pointer to receive array of codec priorities.

Returns:

PJ_SUCCESS on success.

pj_status_t pjmedia_codec_mgr_get_codec_info	(	pjmedia_codec_mgr *	mgr,
		unsigned	pt,
		const pjmedia_codec_info **	inf
	)

Get codec info for the specified static payload type. Note that this can only find codec with static payload types. This function can be used to find codec info for a payload type inside SDP which doesn't have the corresponding rtpmap attribute.

Parameters:

	mgr	The codec manager instance. Application can get the instance by calling pjmedia_endpt_get_codec_mgr().
	pt	Static payload type/number.
	inf	Pointer to receive codec info.

Returns:

PJ_SUCCESS on success.

char* pjmedia_codec_info_to_id	(	const pjmedia_codec_info *	info,
		char *	id,
		unsigned	max_len
	)

Convert codec info struct into a unique codec identifier. A codec identifier looks something like "L16/44100/2".

Parameters:

	info	The codec info
	id	Buffer to put the codec info string.
	max_len	The length of the buffer.

Returns:

The null terminated codec info string, or NULL if the buffer is not long enough.

pj_status_t pjmedia_codec_mgr_find_codecs_by_id	(	pjmedia_codec_mgr *	mgr,
		const pj_str_t *	codec_id,
		unsigned *	count,
		const pjmedia_codec_info *	p_info[],
		unsigned	prio[]
	)

Find codecs by the unique codec identifier. This function will find all codecs that match the codec identifier prefix. For example, if "L16" is specified, then it will find "L16/8000/1", "L16/16000/1", and so on, up to the maximum count specified in the argument.

Parameters:

	mgr	The codec manager instance. Application can get the instance by calling pjmedia_endpt_get_codec_mgr().
	codec_id	The full codec ID or codec ID prefix. If an empty string is given, it will match all codecs.
	count	Maximum number of codecs to find. On return, it contains the actual number of codecs found.
	p_info	Array of pointer to codec info to be filled. This argument may be NULL, which in this case, only codec count will be returned.
	prio	Optional array of codec priorities.

Returns:

PJ_SUCCESS if at least one codec info is found.

pj_status_t pjmedia_codec_mgr_set_codec_priority	(	pjmedia_codec_mgr *	mgr,
		const pj_str_t *	codec_id,
		pj_uint8_t	prio
	)

Set codec priority. The codec priority determines the order of the codec in the SDP created by the endpoint. If more than one codecs are found with the same codec_id prefix, then the function sets the priorities of all those codecs.

Parameters:

	mgr	The codec manager instance. Application can get the instance by calling pjmedia_endpt_get_codec_mgr().
	codec_id	The full codec ID or codec ID prefix. If an empty string is given, it will match all codecs.
	prio	Priority to be set. The priority can have any value between 1 to 255. When the priority is set to zero, the codec will be disabled.

Returns:

PJ_SUCCESS if at least one codec info is found.

pj_status_t pjmedia_codec_mgr_get_default_param	(	pjmedia_codec_mgr *	mgr,
		const pjmedia_codec_info *	info,
		pjmedia_codec_param *	param
	)

Get default codec param for the specified codec info.

Parameters:

	mgr	The codec manager instance. Application can get the instance by calling pjmedia_endpt_get_codec_mgr().
	info	The codec info, which default parameter's is being queried.
	param	On return, will be filled with the default codec parameter.

Returns:

PJ_SUCCESS on success.

pj_status_t pjmedia_codec_mgr_alloc_codec	(	pjmedia_codec_mgr *	mgr,
		const pjmedia_codec_info *	info,
		pjmedia_codec **	p_codec
	)

Request the codec manager to allocate one instance of codec with the specified codec info. The codec will enumerate all codec factories until it finds factory that is able to create the specified codec.

Parameters:

	mgr	The codec manager instance. Application can get the instance by calling pjmedia_endpt_get_codec_mgr().
	info	The information about the codec to be created.
	p_codec	Pointer to receive the codec instance.

Returns:

PJ_SUCCESS on success.

pj_status_t pjmedia_codec_mgr_dealloc_codec	(	pjmedia_codec_mgr *	mgr,
		pjmedia_codec *	codec
	)

Deallocate the specified codec instance. The codec manager will return the instance of the codec back to its factory.

Parameters:

	mgr	The codec manager instance. Application can get the instance by calling pjmedia_endpt_get_codec_mgr().
	codec	The codec instance.

Returns:

PJ_SUCESS on success.