opus_multistream(3) Opus opus_multistream(3)
NAME
opus_multistream - Opus Multistream API
- The multistream API allows individual Opus streams to be combined
into a single packet, enabling support for up to 255 channels.
SYNOPSIS
Typedefs
typedef struct OpusMSEncoder OpusMSEncoder
Opus multistream encoder state.
typedef struct OpusMSDecoder OpusMSDecoder
Opus multistream decoder state.
Multistream encoder functions
opus_int32 opus_multistream_encoder_get_size (int streams, int
coupled_streams)
Gets the size of an OpusMSEncoder structure.
opus_int32 opus_multistream_surround_encoder_get_size (int channels, int
mapping_family)
OpusMSEncoder * opus_multistream_encoder_create (opus_int32 Fs, int
channels, int streams, int coupled_streams, const unsigned char
*mapping, int application, int *error)
Allocates and initializes a multistream encoder state.
OpusMSEncoder * opus_multistream_surround_encoder_create (opus_int32 Fs,
int channels, int mapping_family, int *streams, int
*coupled_streams, unsigned char *mapping, int application, int
*error)
int opus_multistream_encoder_init (OpusMSEncoder *st, opus_int32 Fs, int
channels, int streams, int coupled_streams, const unsigned char
*mapping, int application)
Initialize a previously allocated multistream encoder state.
int opus_multistream_surround_encoder_init (OpusMSEncoder *st,
opus_int32 Fs, int channels, int mapping_family, int *streams, int
*coupled_streams, unsigned char *mapping, int application)
int opus_multistream_encode (OpusMSEncoder *st, const opus_int16 *pcm,
int frame_size, unsigned char *data, opus_int32 max_data_bytes)
Encodes a multistream Opus frame.
int opus_multistream_encode_float (OpusMSEncoder *st, const float *pcm,
int frame_size, unsigned char *data, opus_int32 max_data_bytes)
Encodes a multistream Opus frame from floating point input.
void opus_multistream_encoder_destroy (OpusMSEncoder *st)
Frees an OpusMSEncoder allocated by
opus_multistream_encoder_create().
int opus_multistream_encoder_ctl (OpusMSEncoder *st, int request,...)
Perform a CTL function on a multistream Opus encoder.
Multistream decoder functions
opus_int32 opus_multistream_decoder_get_size (int streams, int
coupled_streams)
Gets the size of an OpusMSDecoder structure.
OpusMSDecoder * opus_multistream_decoder_create (opus_int32 Fs, int
channels, int streams, int coupled_streams, const unsigned char
*mapping, int *error)
Allocates and initializes a multistream decoder state.
int opus_multistream_decoder_init (OpusMSDecoder *st, opus_int32 Fs, int
channels, int streams, int coupled_streams, const unsigned char
*mapping)
Initialize a previously allocated decoder state object.
int opus_multistream_decode (OpusMSDecoder *st, const unsigned char
*data, opus_int32 len, opus_int16 *pcm, int frame_size, int
decode_fec)
Decode a multistream Opus packet.
int opus_multistream_decode_float (OpusMSDecoder *st, const unsigned
char *data, opus_int32 len, float *pcm, int frame_size, int
decode_fec)
Decode a multistream Opus packet with floating point output.
int opus_multistream_decoder_ctl (OpusMSDecoder *st, int request,...)
Perform a CTL function on a multistream Opus decoder.
void opus_multistream_decoder_destroy (OpusMSDecoder *st)
Frees an OpusMSDecoder allocated by
opus_multistream_decoder_create().
Detailed Description
The multistream API allows individual Opus streams to be combined into a
single packet, enabling support for up to 255 channels.
Unlike an elementary Opus stream, the encoder and decoder must negotiate
the channel configuration before the decoder can successfully interpret
the data in the packets produced by the encoder. Some basic information,
such as packet duration, can be computed without any special
negotiation.
The format for multistream Opus packets is defined in RFC 7845 and is
based on the self-delimited Opus framing described in Appendix B of RFC
6716. Normal Opus packets are just a degenerate case of multistream Opus
packets, and can be encoded or decoded with the multistream API by
setting streams to 1 when initializing the encoder or decoder.
Multistream Opus streams can contain up to 255 elementary Opus streams.
These may be either 'uncoupled' or 'coupled', indicating that the
decoder is configured to decode them to either 1 or 2 channels,
respectively. The streams are ordered so that all coupled streams appear
at the beginning.
A mapping table defines which decoded channel i should be used for each
input/output (I/O) channel j. This table is typically provided as an
unsigned char array. Let i = mapping[j] be the index for I/O channel j.
If i < 2*coupled_streams, then I/O channel j is encoded as the left
channel of stream (i/2) if i is even, or as the right channel of stream
(i/2) if i is odd. Otherwise, I/O channel j is encoded as mono in stream
(i - coupled_streams), unless it has the special value 255, in which
case it is omitted from the encoding entirely (the decoder will
reproduce it as silence). Each value i must either be the special value
255 or be less than streams + coupled_streams.
The output channels specified by the encoder should use the Vorbis
channel ordering. A decoder may wish to apply an additional permutation
to the mapping the encoder used to achieve a different output channel
order (e.g. for outputting in WAV order).
Each multistream packet contains an Opus packet for each stream, and all
of the Opus packets in a single multistream packet must have the same
duration. Therefore the duration of a multistream packet can be
extracted from the TOC sequence of the first stream, which is located at
the beginning of the packet, just like an elementary Opus stream:
int nb_samples;
int nb_frames;
nb_frames = opus_packet_get_nb_frames(data, len);
if (nb_frames < 1)
return nb_frames;
nb_samples = opus_packet_get_samples_per_frame(data, 48000) * nb_frames;
The general encoding and decoding process proceeds exactly the same as
in the normal Opus Encoder and Opus Decoder APIs. See their
documentation for an overview of how to use the corresponding
multistream functions.
Typedef Documentation
typedef struct OpusMSDecoder OpusMSDecoder
Opus multistream decoder state. This contains the complete state of a
multistream Opus decoder. It is position independent and can be freely
copied.
See also
opus_multistream_decoder_create
opus_multistream_decoder_init
typedef struct OpusMSEncoder OpusMSEncoder
Opus multistream encoder state. This contains the complete state of a
multistream Opus encoder. It is position independent and can be freely
copied.
See also
opus_multistream_encoder_create
opus_multistream_encoder_init
Function Documentation
int opus_multistream_decode (OpusMSDecoder * st, const unsigned char * data,
opus_int32 len, opus_int16 * pcm, int frame_size, int decode_fec)
Decode a multistream Opus packet.
Parameters
st OpusMSDecoder*: Multistream decoder state.
data const unsigned char*: Input payload. Use a NULL pointer to
indicate packet loss.
len opus_int32: Number of bytes in payload.
pcm opus_int16*: Output signal, with interleaved samples. This must
contain room for frame_size*channels samples.
frame_size int: The number of samples per channel of available space
in pcm. If this is less than the maximum packet duration (120 ms;
5760 for 48kHz), this function will not be capable of decoding some
packets. In the case of PLC (data==NULL) or FEC (decode_fec=1), then
frame_size needs to be exactly the duration of audio that is
missing, otherwise the decoder will not be in the optimal state to
decode the next incoming packet. For the PLC and FEC cases,
frame_size must be a multiple of 2.5 ms.
decode_fec int: Flag (0 or 1) to request that any in-band forward
error correction data be decoded. If no such data is available, the
frame is decoded as if it were lost.
Returns
Number of samples decoded on success or a negative error code (see
Error codes) on failure.
int opus_multistream_decode_float (OpusMSDecoder * st, const unsigned char *
data, opus_int32 len, float * pcm, int frame_size, int decode_fec)
Decode a multistream Opus packet with floating point output.
Parameters
st OpusMSDecoder*: Multistream decoder state.
data const unsigned char*: Input payload. Use a NULL pointer to
indicate packet loss.
len opus_int32: Number of bytes in payload.
pcm opus_int16*: Output signal, with interleaved samples. This must
contain room for frame_size*channels samples.
frame_size int: The number of samples per channel of available space
in pcm. If this is less than the maximum packet duration (120 ms;
5760 for 48kHz), this function will not be capable of decoding some
packets. In the case of PLC (data==NULL) or FEC (decode_fec=1), then
frame_size needs to be exactly the duration of audio that is
missing, otherwise the decoder will not be in the optimal state to
decode the next incoming packet. For the PLC and FEC cases,
frame_size must be a multiple of 2.5 ms.
decode_fec int: Flag (0 or 1) to request that any in-band forward
error correction data be decoded. If no such data is available, the
frame is decoded as if it were lost.
Returns
Number of samples decoded on success or a negative error code (see
Error codes) on failure.
OpusMSDecoder * opus_multistream_decoder_create (opus_int32 Fs, int
channels, int streams, int coupled_streams, const unsigned char *
mapping, int * error)
Allocates and initializes a multistream decoder state. Call
opus_multistream_decoder_destroy() to release this object when finished.
Parameters
Fs opus_int32: Sampling rate to decode at (in Hz). This must be one
of 8000, 12000, 16000, 24000, or 48000.
channels int: Number of channels to output. This must be at most
255. It may be different from the number of coded channels (streams
+ coupled_streams).
streams int: The total number of streams coded in the input. This
must be no more than 255.
coupled_streams int: Number of streams to decode as coupled (2
channel) streams. This must be no larger than the total number of
streams. Additionally, The total number of coded channels (streams +
coupled_streams) must be no more than 255.
mapping const unsigned char[channels]: Mapping from coded channels
to output channels, as described in Opus Multistream API.
error int *: Returns OPUS_OK on success, or an error code (see Error
codes) on failure.
int opus_multistream_decoder_ctl (OpusMSDecoder * st, int request, ...)
Perform a CTL function on a multistream Opus decoder. Generally the
request and subsequent arguments are generated by a convenience macro.
Parameters
st OpusMSDecoder*: Multistream decoder state.
request This and all remaining parameters should be replaced by one
of the convenience macros in Generic CTLs, Decoder related CTLs, or
Multistream specific encoder and decoder CTLs.
See also
Generic CTLs
Decoder related CTLs
Multistream specific encoder and decoder CTLs
void opus_multistream_decoder_destroy (OpusMSDecoder * st)
Frees an OpusMSDecoder allocated by opus_multistream_decoder_create().
Parameters
st OpusMSDecoder: Multistream decoder state to be freed.
opus_int32 opus_multistream_decoder_get_size (int streams, int
coupled_streams)
Gets the size of an OpusMSDecoder structure.
Parameters
streams int: The total number of streams coded in the input. This
must be no more than 255.
coupled_streams int: Number streams to decode as coupled (2 channel)
streams. This must be no larger than the total number of streams.
Additionally, The total number of coded channels (streams +
coupled_streams) must be no more than 255.
Returns
The size in bytes on success, or a negative error code (see Error
codes) on error.
int opus_multistream_decoder_init (OpusMSDecoder * st, opus_int32 Fs, int
channels, int streams, int coupled_streams, const unsigned char *
mapping)
Initialize a previously allocated decoder state object. The memory
pointed to by st must be at least the size returned by
opus_multistream_encoder_get_size(). This is intended for applications
which use their own allocator instead of malloc. To reset a previously
initialized state, use the OPUS_RESET_STATE CTL.
See also
opus_multistream_decoder_create
opus_multistream_deocder_get_size
Parameters
st OpusMSEncoder*: Multistream encoder state to initialize.
Fs opus_int32: Sampling rate to decode at (in Hz). This must be one
of 8000, 12000, 16000, 24000, or 48000.
channels int: Number of channels to output. This must be at most
255. It may be different from the number of coded channels (streams
+ coupled_streams).
streams int: The total number of streams coded in the input. This
must be no more than 255.
coupled_streams int: Number of streams to decode as coupled (2
channel) streams. This must be no larger than the total number of
streams. Additionally, The total number of coded channels (streams +
coupled_streams) must be no more than 255.
mapping const unsigned char[channels]: Mapping from coded channels
to output channels, as described in Opus Multistream API.
Returns
OPUS_OK on success, or an error code (see Error codes) on failure.
int opus_multistream_encode (OpusMSEncoder * st, const opus_int16 * pcm, int
frame_size, unsigned char * data, opus_int32 max_data_bytes)
Encodes a multistream Opus frame.
Parameters
st OpusMSEncoder*: Multistream encoder state.
pcm const opus_int16*: The input signal as interleaved samples. This
must contain frame_size*channels samples.
frame_size int: Number of samples per channel in the input signal.
This must be an Opus frame size for the encoder's sampling rate. For
example, at 48 kHz the permitted values are 120, 240, 480, 960,
1920, and 2880. Passing in a duration of less than 10 ms (480
samples at 48 kHz) will prevent the encoder from using the LPC or
hybrid modes.
data unsigned char*: Output payload. This must contain storage for
at least max_data_bytes.
max_data_bytes opus_int32: Size of the allocated memory for the
output payload. This may be used to impose an upper limit on the
instant bitrate, but should not be used as the only bitrate control.
Use OPUS_SET_BITRATE to control the bitrate.
Returns
The length of the encoded packet (in bytes) on success or a negative
error code (see Error codes) on failure.
int opus_multistream_encode_float (OpusMSEncoder * st, const float * pcm,
int frame_size, unsigned char * data, opus_int32 max_data_bytes)
Encodes a multistream Opus frame from floating point input.
Parameters
st OpusMSEncoder*: Multistream encoder state.
pcm const float*: The input signal as interleaved samples with a
normal range of +/-1.0. Samples with a range beyond +/-1.0 are
supported but will be clipped by decoders using the integer API and
should only be used if it is known that the far end supports
extended dynamic range. This must contain frame_size*channels
samples.
frame_size int: Number of samples per channel in the input signal.
This must be an Opus frame size for the encoder's sampling rate. For
example, at 48 kHz the permitted values are 120, 240, 480, 960,
1920, and 2880. Passing in a duration of less than 10 ms (480
samples at 48 kHz) will prevent the encoder from using the LPC or
hybrid modes.
data unsigned char*: Output payload. This must contain storage for
at least max_data_bytes.
max_data_bytes opus_int32: Size of the allocated memory for the
output payload. This may be used to impose an upper limit on the
instant bitrate, but should not be used as the only bitrate control.
Use OPUS_SET_BITRATE to control the bitrate.
Returns
The length of the encoded packet (in bytes) on success or a negative
error code (see Error codes) on failure.
OpusMSEncoder * opus_multistream_encoder_create (opus_int32 Fs, int
channels, int streams, int coupled_streams, const unsigned char *
mapping, int application, int * error)
Allocates and initializes a multistream encoder state. Call
opus_multistream_encoder_destroy() to release this object when finished.
Parameters
Fs opus_int32: Sampling rate of the input signal (in Hz). This must
be one of 8000, 12000, 16000, 24000, or 48000.
channels int: Number of channels in the input signal. This must be
at most 255. It may be greater than the number of coded channels
(streams + coupled_streams).
streams int: The total number of streams to encode from the input.
This must be no more than the number of channels.
coupled_streams int: Number of coupled (2 channel) streams to
encode. This must be no larger than the total number of streams.
Additionally, The total number of encoded channels (streams +
coupled_streams) must be no more than the number of input channels.
mapping const unsigned char[channels]: Mapping from encoded channels
to input channels, as described in Opus Multistream API. As an extra
constraint, the multistream encoder does not allow encoding coupled
streams for which one channel is unused since this is never a good
idea.
application int: The target encoder application. This must be one of
the following:
OPUS_APPLICATION_VOIP
Process signal for improved speech intelligibility.
OPUS_APPLICATION_AUDIO
Favor faithfulness to the original input.
OPUS_APPLICATION_RESTRICTED_LOWDELAY
Configure the minimum possible coding delay by disabling certain
modes of operation.
error int *: Returns OPUS_OK on success, or an error code (see Error
codes) on failure.
int opus_multistream_encoder_ctl (OpusMSEncoder * st, int request, ...)
Perform a CTL function on a multistream Opus encoder. Generally the
request and subsequent arguments are generated by a convenience macro.
Parameters
st OpusMSEncoder*: Multistream encoder state.
request This and all remaining parameters should be replaced by one
of the convenience macros in Generic CTLs, Encoder related CTLs, or
Multistream specific encoder and decoder CTLs.
See also
Generic CTLs
Encoder related CTLs
Multistream specific encoder and decoder CTLs
void opus_multistream_encoder_destroy (OpusMSEncoder * st)
Frees an OpusMSEncoder allocated by opus_multistream_encoder_create().
Parameters
st OpusMSEncoder*: Multistream encoder state to be freed.
opus_int32 opus_multistream_encoder_get_size (int streams, int
coupled_streams)
Gets the size of an OpusMSEncoder structure.
Parameters
streams int: The total number of streams to encode from the input.
This must be no more than 255.
coupled_streams int: Number of coupled (2 channel) streams to
encode. This must be no larger than the total number of streams.
Additionally, The total number of encoded channels (streams +
coupled_streams) must be no more than 255.
Returns
The size in bytes on success, or a negative error code (see Error
codes) on error.
int opus_multistream_encoder_init (OpusMSEncoder * st, opus_int32 Fs, int
channels, int streams, int coupled_streams, const unsigned char *
mapping, int application)
Initialize a previously allocated multistream encoder state. The memory
pointed to by st must be at least the size returned by
opus_multistream_encoder_get_size(). This is intended for applications
which use their own allocator instead of malloc. To reset a previously
initialized state, use the OPUS_RESET_STATE CTL.
See also
opus_multistream_encoder_create
opus_multistream_encoder_get_size
Parameters
st OpusMSEncoder*: Multistream encoder state to initialize.
Fs opus_int32: Sampling rate of the input signal (in Hz). This must
be one of 8000, 12000, 16000, 24000, or 48000.
channels int: Number of channels in the input signal. This must be
at most 255. It may be greater than the number of coded channels
(streams + coupled_streams).
streams int: The total number of streams to encode from the input.
This must be no more than the number of channels.
coupled_streams int: Number of coupled (2 channel) streams to
encode. This must be no larger than the total number of streams.
Additionally, The total number of encoded channels (streams +
coupled_streams) must be no more than the number of input channels.
mapping const unsigned char[channels]: Mapping from encoded channels
to input channels, as described in Opus Multistream API. As an extra
constraint, the multistream encoder does not allow encoding coupled
streams for which one channel is unused since this is never a good
idea.
application int: The target encoder application. This must be one of
the following:
OPUS_APPLICATION_VOIP
Process signal for improved speech intelligibility.
OPUS_APPLICATION_AUDIO
Favor faithfulness to the original input.
OPUS_APPLICATION_RESTRICTED_LOWDELAY
Configure the minimum possible coding delay by disabling certain
modes of operation.
Returns
OPUS_OK on success, or an error code (see Error codes) on failure.
OpusMSEncoder * opus_multistream_surround_encoder_create (opus_int32 Fs, int
channels, int mapping_family, int * streams, int * coupled_streams,
unsigned char * mapping, int application, int * error)
opus_int32 opus_multistream_surround_encoder_get_size (int channels, int
mapping_family)
int opus_multistream_surround_encoder_init (OpusMSEncoder * st, opus_int32
Fs, int channels, int mapping_family, int * streams, int *
coupled_streams, unsigned char * mapping, int application)
Author
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