169 lines
8.0 KiB
C++
169 lines
8.0 KiB
C++
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/*
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* Lc3Config.hpp
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*
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* Copyright 2019 HIMSA II K/S - www.himsa.dk. Represented by EHIMA - www.ehima.com
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef __LC3_CONFIG_HPP_
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#define __LC3_CONFIG_HPP_
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#include <cstdint>
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/*
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* The LC3 encoder and decoder have a common set of essential session
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* configuration parameters - see LC3 specification Sections 2.2 "Encoder interfaces"
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* and Section 2.4 "Decoder interfaces" (dr09r07).
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* The set of common session configuration parameters is represented
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* by an instance of class Lc3Config.
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*
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* Lc3Config is designed such that all parameters need to be
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* providing when constructing an instance. Afterwards, success of creation,
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* the actual parameter values, and derived parameter values are provided
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* by corresponding const getter methods or public const fields.
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*
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* When parameters need to be changes, a new instance of Lc3Config has to be
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* created.
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*
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* Instances of Lc3Config are provided to instances of Lc3Encoder and Lc3Decoder
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* when constructing them.
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*
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* The main purpose of Lc3Config is to verify and handle common LC3 session
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* configuration parameters in a consistent way.
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*
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*/
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class Lc3Config
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{
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public:
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/*
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* Enumeration of supported frame durations N_ms = 7.5ms and N_ms = 10ms.
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*
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* Note: although the LC3 specification describes frame duration N_ms as
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* a parameter with floating point values 7.5 and 10.0, we decided
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* to make this parameter a discrete enumeration of supported
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* frame durations. There are too many codec parts that need
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* specifically listed constants dependent on the configured
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* frame duration, so that it never will be possible to chose from a
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* larger set of floating point values for N_ms.
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* Making the data type of N_ms an enumeration supports
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* straight forwards verification that meaningful parameters are given.
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*/
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enum class FrameDuration
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{
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d10ms,
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d7p5ms
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};
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// configuration error (see "getErrorStatus")
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static const uint8_t ERROR_FREE = 0x00;
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static const uint8_t INVALID_SAMPLING_RATE = 0x01;
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static const uint8_t INVALID_FRAME_DURATION = 0x02;
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static const uint8_t INVALID_NUMBER_OF_CHANNELS = 0x04;
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/*
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* Constructor of an instance of Lc3Config
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* Parameters:
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* (see also see LC3 specification Sections 2.2 "Encoder interfaces"
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* and Section 2.4 "Decoder interfaces" (dr09r07) )
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*
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* Fs_ : Sampling frequency in Hz -> defines public constant Fs
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* Supported values are
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* 8000 Hz
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* 16000 Hz
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* 24000 Hz
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* 32000 Hz
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* 44100 Hz
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* 48000 Hz
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*
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* N_ms_ : Frame duration given by value from enumeration FrameDuration (see above)
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* -> defines public constant N_ms
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* Supported values see enumeration FrameDuration.
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*
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* Nc_ : Number of channels -> defines public constant Nc
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* Supported values are Nc > 0 and Nc < 256 such that device resources are not exhausted.
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* Notes:
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* - Exhausting device resources can mean that there is not enough memory
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* to instantiate the corresponding number of encoders and/or decoders, but
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* also that computing the encoders and/or decoders in real-time is not possible.
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* - The parameter N_c_max described in the LC3 specifciation is not given here,
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* since there is too little knowledge on the target devices where this code
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* may be used.
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*
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*/
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Lc3Config(uint16_t Fs_, FrameDuration N_ms_, uint8_t Nc_);
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// no default constructor supported
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Lc3Config() = delete;
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// Destructor
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virtual ~Lc3Config();
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/*
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* Getter "isValid" provides a convenience function that returns true when an instance of Lc3Config
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* could be created without error.
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*/
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bool isValid() const;
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/*
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* Getter "getErrorStatus" provides details on the success of instantiating Lc3Config.
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* The possible return values are listed as constants in this class (see configuration error constants above)
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*/
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uint8_t getErrorStatus() const;
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/*
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* Getter "getByteCountFromBitrate" provides the number of bytes available in one encoded frame
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* of one channel (see "nbytes" as described in Section 3.2.5 "Bit budget and bitrate" (dr09r07) )
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*
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* The number of bytes "nbytes" to use for encoding a single channel is a required external input to
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* each single channel LC3 encoder. The same number of bytes (now to be used for decoding) is also
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* a required external input to each single channel LC3 decoder. The corresponding number of bits
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* available in one frame is thus "nbits 8*nbytes". And the bitrate of the codec in bits per second
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* is then "bitrate = nbits / frame_duration = nbits*Fs/NF = 8*nbytes*Fs/NF".
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* The codec works on a byte boundery, i.e. the variable "nbytes" shall be an integer number.
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* A certain "bitrate" can be converted to a number of bytes "nbytes" where the number of bytes is
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* rounded towards the nearest lower integer.
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*
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* The algorithm is verified from the bitrate corresonding to
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* nbytes = 20 up to the bitrate corresponding to
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* nbytes = 400 per channel for all sampling rates.
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* The LC3 specification does not specify or recommend what bitrate to use for encoding a frame of
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* audio saples. This is specified by the profiles making use of the LC3.
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*/
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uint16_t getByteCountFromBitrate(uint32_t bitrate) const; // meant for a single channel
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private:
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// internal utilities used for verifying the given input parameters and computing derived parameters
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uint8_t getFs_ind(uint16_t Fs);
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uint16_t getNF(uint16_t Fs, FrameDuration N_ms);
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uint16_t getNE(uint16_t NF, FrameDuration N_ms);
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// errors status set during construction and returned by getErrorStatus()
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uint8_t errorStatus;
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public:
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// configuration details -> see also Section 3.1.2 "Mathematical symbols" (dr09r07)
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const uint16_t Fs; // Sampling rate (in Hz)
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const uint8_t Fs_ind; // Sampling rate index (see also Section 3.2.2 "Sampling rates" (dr09r07)
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const FrameDuration N_ms; // Frame duration -> see Lc3Config constructor documentation
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// Note: that the actual frame duration is longer by a factor of 480/441
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// if the sampling rate is 44100 Hz
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const uint16_t NF; // Number of samples processed in one frame of one channel (also known as frame size)
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const uint16_t NE; // Number of encoded spectral lines (per frame and channel)
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const uint16_t Z; // Number of leading zeros in MDCT window
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const uint8_t Nc; // Number of channels
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const uint8_t N_b; // Number of bands
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};
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#endif // __LC3_CONFIG_HPP_
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