129 lines
4.1 KiB
Go
129 lines
4.1 KiB
Go
package silk
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import (
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"fmt"
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"github.com/pion/opus/internal/rangecoding"
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)
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type (
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frameSignalType byte
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frameQuantizationOffsetType byte
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)
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const (
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nanoseconds20Ms = 20000000
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frameSignalTypeInactive frameSignalType = iota + 1
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frameSignalTypeUnvoiced
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frameSignalTypeVoiced
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frameQuantizationOffsetTypeLow frameQuantizationOffsetType = iota + 1
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frameQuantizationOffsetTypeHigh
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)
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var (
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// +----------+-----------------------------+
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// | VAD Flag | PDF |
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// +----------+-----------------------------+
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// | Inactive | {26, 230, 0, 0, 0, 0}/256 |
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// | | |
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// | Active | {0, 0, 24, 74, 148, 10}/256 |
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// +----------+-----------------------------+
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//
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// https://datatracker.ietf.org/doc/html/rfc6716#section-4.2.7.3
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icdfFrameTypeVADInactive = []uint{256, 26, 256}
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icdfFrameTypeVADActive = []uint{256, 24, 98, 246, 256}
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)
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// Decoder maintains the state needed to decode a stream
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// of Silk frames
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type Decoder struct {
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rangeDecoder rangecoding.Decoder
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}
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// NewDecoder creates a new Silk Decoder
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func NewDecoder() *Decoder {
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return &Decoder{}
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}
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// Decode decodes many SILK subframes
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func (d *Decoder) Decode(in []byte, isStereo bool, nanoseconds int) (decoded []byte, err error) {
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if nanoseconds != nanoseconds20Ms {
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return nil, errUnsupportedSilkFrameDuration
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} else if isStereo {
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return nil, errUnsupportedSilkStereo
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}
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d.rangeDecoder.Init(in)
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//The LP layer begins with two to eight header bits These consist of one
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// Voice Activity Detection (VAD) bit per frame (up to 3), followed by a
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// single flag indicating the presence of LBRR frames.
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// https://datatracker.ietf.org/doc/html/rfc6716#section-4.2.3
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voiceActivityDetected := d.rangeDecoder.DecodeSymbolLogP(1) == 1
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lowBitRateRedundancy := d.rangeDecoder.DecodeSymbolLogP(1) == 1
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if lowBitRateRedundancy {
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return nil, errUnsupportedSilkLowBitrateRedundancy
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}
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// Each SILK frame contains a single "frame type" symbol that jointly
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// codes the signal type and quantization offset type of the
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// corresponding frame.
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//
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// https://datatracker.ietf.org/doc/html/rfc6716#section-4.2.7.3
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var frameTypeSymbol uint32
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if voiceActivityDetected {
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frameTypeSymbol = d.rangeDecoder.DecodeSymbolWithICDF(icdfFrameTypeVADActive)
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} else {
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frameTypeSymbol = d.rangeDecoder.DecodeSymbolWithICDF(icdfFrameTypeVADInactive)
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}
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// +------------+-------------+--------------------------+
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// | Frame Type | Signal Type | Quantization Offset Type |
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// +------------+-------------+--------------------------+
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// | 0 | Inactive | Low |
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// | | | |
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// | 1 | Inactive | High |
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// | | | |
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// | 2 | Unvoiced | Low |
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// | | | |
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// | 3 | Unvoiced | High |
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// | | | |
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// | 4 | Voiced | Low |
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// | | | |
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// | 5 | Voiced | High |
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// +------------+-------------+--------------------------+
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//
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// https://datatracker.ietf.org/doc/html/rfc6716#section-4.2.7.3
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signalType := frameSignalType(0)
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quantizationOffsetType := frameQuantizationOffsetType(0)
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switch frameTypeSymbol {
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case 0:
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signalType = frameSignalTypeInactive
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quantizationOffsetType = frameQuantizationOffsetTypeLow
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case 1:
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signalType = frameSignalTypeInactive
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quantizationOffsetType = frameQuantizationOffsetTypeHigh
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case 2:
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signalType = frameSignalTypeUnvoiced
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quantizationOffsetType = frameQuantizationOffsetTypeLow
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case 3:
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signalType = frameSignalTypeUnvoiced
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quantizationOffsetType = frameQuantizationOffsetTypeHigh
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case 4:
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signalType = frameSignalTypeVoiced
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quantizationOffsetType = frameQuantizationOffsetTypeLow
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case 5:
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signalType = frameSignalTypeVoiced
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quantizationOffsetType = frameQuantizationOffsetTypeHigh
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}
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fmt.Println(signalType)
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fmt.Println(quantizationOffsetType)
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return
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}
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