Learning Libopus (1) Encoder encoder

From: Http://www.opus-codec.org/docs/html_api-1.1.0/group__opus__encoder.html#gaefeb7dc1d6e3b59dea5ea674c86e9c18

Detailed description

This page describes the use procedures and features for encoding.


Since Opus is a state codec, it is necessary to create an encoder before encoding. You can do this:


int error;
Opusencoder *enc;
ENC = opus_encoder_create (Fs, channels, application, &error);


From there, the enc can be used to encode the audio stream. This encoder cannot encode multiple streams at the same time (thread insecure). At the same time, when encoding multiple frames, the encoder does not need to repeat initialization.


When you call Opus_encoder_create (), the memory space is created, and it can initialize the pre-allocated memory:


int size;
int error;
Opusencoder *enc;
Size = opus_encoder_get_size (channels);
ENC = malloc (size);
Error = Opus_encoder_init (enc, Fs, channels, application);


Opus_encoder_get_size () returns the memory size required by the encoder. Please note that this size may be modified in future versions, so try not to use constants instead.


The encoder is assigned to a contiguous block of memory that can be obtained by a shallow copy (e.g. memcpy)


You can modify the internal settings of the encoder by Opus_encoder_ctl (). These settings use the recommended values by default. The following are the most common modifications:


Opus_encoder_ctl (Enc, opus_set_bitrate (bitrate));//baud rate
Opus_encoder_ctl (ENC, opus_set_complexity (complexity));//complexity
Opus_encoder_ctl (Enc, opus_set_signal (Signal_type));//Signal
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Bitrate units are bits per second (b/s)


Complexity is a value from 1 to 10, where 1 is the lowest and 10 is the highest


Signal_type either Opus_auto (default), Opus_signal_voice or Opus_signal_music


See encoder-related CTL and common CTL for a complete list of settings. Most parameters can be set or modified when the stream is encoded.


Must be a complete audio data (2.5,5,10,20,40 or 60 milliseconds) when calling Opus_encode () or opus_encode_float ():


Len = Opus_encode (enc, audio_frame, frame_size, Packet, max_packet);
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Audio_frame is opus_int16 audio data (or opus_encode_float ())


Frame_size is the duration of the sample in the frame (per channel)


Packet is an array of bytes that the audio data needs to write


Max_packet is the maximum number of bytes that can be written in the package (4000 bytes recommended). Do not control the bitrate of VBR via Max_packet, use opus_set_bitrate CTL if necessary.


Opus_encode () and Opus_encode_float () return the actual number of bytes written to the packet. The return value can be negative, which indicates an error has occurred. If the return value is 1 bytes, the grouping does not need to be sent (DTX).


When you need to release the encoder, you can pass:
Opus_encoder_destroy (ENC);


If the encoder is created with Opus_encoder_init () instead of opus_encoder_create (), nothing is done, only the pre-allocated memory is freed, and the call to free (ENC)