Alex X
88 lines
1.5 KiB
Go
88 lines
1.5 KiB
Go
package opus
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import (
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"time"
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)
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type Header struct {
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Mode string
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SampleRate uint16
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FrameSize time.Duration
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Channels byte
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Frames byte
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}
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func UnmarshalHeader(b []byte) *Header {
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// https://datatracker.ietf.org/doc/html/rfc6716#section-3.1
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b0 := b[0]
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config := b0 >> 3
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return &Header{
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Mode: parseMode(config),
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SampleRate: parseSampleRate(config),
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FrameSize: parseFrameSize(config),
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Channels: parseChannels(b0 >> 2 & 0b1),
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Frames: parseFrames(b0 & 0b11),
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}
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}
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func parseMode(config byte) string {
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if config <= 11 {
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return "silk"
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}
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if config <= 15 {
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return "hybrid"
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}
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return "celt"
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}
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func parseSampleRate(config byte) uint16 {
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switch config {
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case 0, 1, 2, 3, 16, 17, 18, 19:
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return 8000 // NB (narrowband)
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case 4, 5, 6, 7:
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return 12000 // MB (medium-band)
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case 8, 9, 10, 11, 20, 21, 22, 23:
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return 16000 // WB (wideband)
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case 12, 13, 24, 25, 26, 27:
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return 24000 // SWB (super-wideband)
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case 14, 15, 28, 29, 30, 31:
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return 48000 // FB (fullband)
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}
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return 0
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}
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func parseFrameSize(config byte) time.Duration {
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switch config {
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case 0, 4, 8, 12, 14, 18, 22, 26, 30:
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return 10_000_000
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case 1, 5, 9, 13, 15, 19, 23, 27, 31:
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return 20_000_000
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case 2, 6, 10:
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return 40_000_000
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case 3, 7, 11:
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return 60_000_000
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case 16, 20, 24, 28:
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return 2_500_000
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case 17, 21, 25, 29:
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return 5_000_000
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}
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return 0
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}
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func parseChannels(s byte) byte {
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if s == 1 {
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return 2
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}
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return 1
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}
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func parseFrames(c byte) byte {
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switch c {
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case 0:
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return 1
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case 1, 2:
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return 2
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}
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return 0xFF
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}
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