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avframes
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refactor

This commit is contained in:
Rob Watson 2021-01-28 00:01:05 +01:00
parent c612714efa
commit 470a543ca1
4 changed files with 186 additions and 181 deletions
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1
internal/mpeg/mpeg.go
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@ -1 +0,0 @@
package mpeg

154
main.go
View File

@ -6,160 +6,12 @@ import (
"io"
"log"
"os"
"git.netflux.io/rob/avframes/pkg/mpeg"
)
const fname = "/home/rob/share/home-office/example.mp3"
type (
AudioVersionId int
Layer int
)
type Decoder struct{}
const (
AudioVersionMPEG25 AudioVersionId = iota
AudioVersionReserved
AudioVersionMPEG2
AudioVersionMPEG1
)
const (
LayerReserved Layer = iota
LayerIII
LayerII
LayerI
)
var (
bitRates = [5][16]int{
{0, 32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448, 0},
{0, 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384, 0},
{0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 0},
{0, 32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256, 0},
{0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, 0},
}
sampleRates = [4][4]int{
{11025, 12000, 8000, 0},
{0, 0, 0, 0},
{22050, 24000, 16000, 0},
{44100, 48000, 32000, 0},
}
samplesPerFrame = [4][4]int{
{0, 576, 1152, 384},
{0, 0, 0, 0},
{0, 576, 1152, 384},
{0, 1152, 1152, 384},
}
)
type header []byte
func (h header) HasSyncWord() bool {
return h[0] == 0xff && h[1]&0xe0 == 0xe0
}
func (h header) AudioVersionId() AudioVersionId {
return AudioVersionId((h[1] >> 3) & 0x3)
}
func (h header) Layer() Layer {
return Layer((h[1] >> 1) & 0x3)
}
func (h header) IsProtected() bool {
return h[1]&1 == 1
}
func (h header) String() string {
return fmt.Sprintf("%08b", h)
}
func (h header) SamplesPerFrame() int {
return samplesPerFrame[h.AudioVersionId()][h.Layer()]
}
func (h header) SampleRate() int {
i := h.AudioVersionId()
j := (h[2] >> 2) & 0x3
return sampleRates[i][j]
}
func (h header) PaddingBytes() int {
if isPadded := (h[2] >> 1) & 1; isPadded == 0 {
return 0
}
switch h.Layer() {
case LayerI:
return 4
case LayerII, LayerIII:
return 1
default:
return 0
}
}
func (h header) IsValid() bool {
if len(h) < 4 {
return false
}
if !h.HasSyncWord() {
return false
}
if h.AudioVersionId() == AudioVersionReserved {
return false
}
if h.Layer() == LayerReserved {
return false
}
if h.BitRate() == 0 {
return false
}
if h.SampleRate() == 0 {
return false
}
return true
}
func (h header) Len() int {
// TODO premultiply bitrates?
bps := float64(h.SamplesPerFrame()) / 8
return int((bps*float64(h.BitRate()*1000))/float64(h.SampleRate()) + float64(h.PaddingBytes()))
}
func (h header) BitRate() int {
// TODO: improve this
var j int
switch h.AudioVersionId() {
case AudioVersionMPEG1:
switch h.Layer() {
case LayerIII:
j = 2
case LayerII:
j = 1
case LayerI:
j = 0
default:
return 0
}
case AudioVersionReserved:
return 0
case AudioVersionMPEG2, AudioVersionMPEG25:
switch h.Layer() {
case LayerIII, LayerII:
j = 4
case LayerI:
j = 3
default:
return 0
}
}
return bitRates[j][h[2]>>4]
}
func main() {
f, err := os.Open(fname)
if err != nil {
@ -179,7 +31,7 @@ func main() {
log.Fatal(err)
}
if h := header(buf); h.IsValid() {
if h := mpeg.Header(buf); h.IsValid() {
fmt.Printf("Got header: %v, audio version: %d, layer index: %d, bitrate: %d, samplerate: %d, samplesPerFrame: %d, padding: %d, size: %d\n", h, h.AudioVersionId(), h.Layer(), h.BitRate(), h.SampleRate(), h.SamplesPerFrame(), h.PaddingBytes(), h.Len())
bufreader.Discard(h.Len() - 4)
} else {

153
pkg/mpeg/mpeg.go Normal file
View File

@ -0,0 +1,153 @@
package mpeg
import "fmt"
type (
AudioVersionId int
Layer int
)
type Decoder struct{}
const (
AudioVersionMPEG25 AudioVersionId = iota
AudioVersionReserved
AudioVersionMPEG2
AudioVersionMPEG1
)
const (
LayerReserved Layer = iota
LayerIII
LayerII
LayerI
)
var (
bitRates = [5][16]int{
{0, 32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448, 0},
{0, 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384, 0},
{0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 0},
{0, 32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256, 0},
{0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, 0},
}
sampleRates = [4][4]int{
{11025, 12000, 8000, 0},
{0, 0, 0, 0},
{22050, 24000, 16000, 0},
{44100, 48000, 32000, 0},
}
samplesPerFrame = [4][4]int{
{0, 576, 1152, 384},
{0, 0, 0, 0},
{0, 576, 1152, 384},
{0, 1152, 1152, 384},
}
)
type Header []byte
func (h Header) HasSyncWord() bool {
return h[0] == 0xff && h[1]&0xe0 == 0xe0
}
func (h Header) AudioVersionId() AudioVersionId {
return AudioVersionId((h[1] >> 3) & 0x3)
}
func (h Header) Layer() Layer {
return Layer((h[1] >> 1) & 0x3)
}
func (h Header) IsProtected() bool {
return h[1]&1 == 1
}
func (h Header) String() string {
return fmt.Sprintf("%08b", h)
}
func (h Header) SamplesPerFrame() int {
return samplesPerFrame[h.AudioVersionId()][h.Layer()]
}
func (h Header) SampleRate() int {
i := h.AudioVersionId()
j := (h[2] >> 2) & 0x3
return sampleRates[i][j]
}
func (h Header) PaddingBytes() int {
if isPadded := (h[2] >> 1) & 1; isPadded == 0 {
return 0
}
switch h.Layer() {
case LayerI:
return 4
case LayerII, LayerIII:
return 1
default:
return 0
}
}
func (h Header) IsValid() bool {
if len(h) < 4 {
return false
}
if !h.HasSyncWord() {
return false
}
if h.AudioVersionId() == AudioVersionReserved {
return false
}
if h.Layer() == LayerReserved {
return false
}
if h.BitRate() == 0 {
return false
}
if h.SampleRate() == 0 {
return false
}
return true
}
func (h Header) Len() int {
// TODO premultiply bitrates?
bps := float64(h.SamplesPerFrame()) / 8
return int((bps*float64(h.BitRate()*1000))/float64(h.SampleRate()) + float64(h.PaddingBytes()))
}
func (h Header) BitRate() int {
// TODO: improve this
var j int
switch h.AudioVersionId() {
case AudioVersionMPEG1:
switch h.Layer() {
case LayerIII:
j = 2
case LayerII:
j = 1
case LayerI:
j = 0
default:
return 0
}
case AudioVersionReserved:
return 0
case AudioVersionMPEG2, AudioVersionMPEG25:
switch h.Layer() {
case LayerIII, LayerII:
j = 4
case LayerI:
j = 3
default:
return 0
}
}
return bitRates[j][h[2]>>4]
}

59
main_test.go → pkg/mpeg/mpeg_test.go
View File

@ -1,8 +1,9 @@
package main
package mpeg_test
import (
"testing"
"git.netflux.io/rob/avframes/pkg/mpeg"
"github.com/stretchr/testify/assert"
)
@ -13,7 +14,7 @@ func TestHasSyncWord(t *testing.T) {
expResult bool
}{
{
"empty header",
"empty mpeg.Header",
[]byte{0, 0, 0, 0},
false,
},
@ -28,7 +29,7 @@ func TestHasSyncWord(t *testing.T) {
true,
},
{
"full header",
"full mpeg.Header",
[]byte{0xff, 0xff, 0xff, 0xff},
true,
},
@ -36,7 +37,7 @@ func TestHasSyncWord(t *testing.T) {
for _, tc := range testCases {
t.Run(tc.name, func(t *testing.T) {
h := header(tc.bytes)
h := mpeg.Header(tc.bytes)
assert.Equal(t, tc.expResult, h.HasSyncWord())
})
}
@ -44,38 +45,38 @@ func TestHasSyncWord(t *testing.T) {
func TestAudioVersionId(t *testing.T) {
bytes := []byte{0xff, 0xe8, 0, 0}
h := header(bytes)
assert.Equal(t, AudioVersionReserved, h.AudioVersionId())
h := mpeg.Header(bytes)
assert.Equal(t, mpeg.AudioVersionReserved, h.AudioVersionId())
bytes = []byte{0xff, 0xf0, 0, 0}
h = header(bytes)
assert.Equal(t, AudioVersionMPEG2, h.AudioVersionId())
h = mpeg.Header(bytes)
assert.Equal(t, mpeg.AudioVersionMPEG2, h.AudioVersionId())
bytes = []byte{0xff, 0xff, 0, 0}
h = header(bytes)
assert.Equal(t, AudioVersionMPEG1, h.AudioVersionId())
h = mpeg.Header(bytes)
assert.Equal(t, mpeg.AudioVersionMPEG1, h.AudioVersionId())
bytes = []byte{0xff, 0xe0, 0, 0}
h = header(bytes)
assert.Equal(t, AudioVersionMPEG25, h.AudioVersionId())
h = mpeg.Header(bytes)
assert.Equal(t, mpeg.AudioVersionMPEG25, h.AudioVersionId())
}
func TestLayer(t *testing.T) {
bytes := []byte{0xff, 0xe0, 0, 0}
h := header(bytes)
assert.Equal(t, LayerReserved, h.Layer())
h := mpeg.Header(bytes)
assert.Equal(t, mpeg.LayerReserved, h.Layer())
bytes = []byte{0xff, 0xe2, 0, 0}
h = header(bytes)
assert.Equal(t, LayerIII, h.Layer())
h = mpeg.Header(bytes)
assert.Equal(t, mpeg.LayerIII, h.Layer())
bytes = []byte{0xff, 0xe4, 0, 0}
h = header(bytes)
assert.Equal(t, LayerII, h.Layer())
h = mpeg.Header(bytes)
assert.Equal(t, mpeg.LayerII, h.Layer())
bytes = []byte{0xff, 0xe6, 0, 0}
h = header(bytes)
assert.Equal(t, LayerI, h.Layer())
h = mpeg.Header(bytes)
assert.Equal(t, mpeg.LayerI, h.Layer())
}
func TestPaddingBytes(t *testing.T) {
@ -118,7 +119,7 @@ func TestPaddingBytes(t *testing.T) {
for _, tc := range testCases {
t.Run(tc.name, func(t *testing.T) {
h := header(tc.bytes)
h := mpeg.Header(tc.bytes)
assert.Equal(t, tc.expPadding, h.PaddingBytes())
})
}
@ -126,11 +127,11 @@ func TestPaddingBytes(t *testing.T) {
func TestIsProtected(t *testing.T) {
bytes := []byte{0xff, 0xe1, 0, 0}
h := header(bytes)
h := mpeg.Header(bytes)
assert.True(t, h.IsProtected())
bytes = []byte{0xff, 0xe0, 0, 0}
h = header(bytes)
h = mpeg.Header(bytes)
assert.False(t, h.IsProtected())
}
@ -204,7 +205,7 @@ func TestSamplesPerFrame(t *testing.T) {
for _, tc := range testCases {
t.Run(tc.name, func(t *testing.T) {
h := header(tc.bytes)
h := mpeg.Header(tc.bytes)
assert.Equal(t, tc.expSamplesPerFrame, h.SamplesPerFrame())
})
}
@ -217,7 +218,7 @@ func TestBitRate(t *testing.T) {
expBitRate int
}{
{
"empty header",
"empty mpeg.Header",
[]byte{0, 0, 0, 0},
0,
},
@ -332,7 +333,7 @@ func TestBitRate(t *testing.T) {
160,
},
{
"full header",
"full mpeg.Header",
[]byte{1, 1, 1, 1},
0,
},
@ -340,7 +341,7 @@ func TestBitRate(t *testing.T) {
for _, tc := range testCases {
t.Run(tc.name, func(t *testing.T) {
h := header(tc.bytes)
h := mpeg.Header(tc.bytes)
assert.Equal(t, tc.expBitRate, h.BitRate())
})
}
@ -416,7 +417,7 @@ func TestSampleRate(t *testing.T) {
for _, tc := range testCases {
t.Run(tc.name, func(t *testing.T) {
h := header(tc.bytes)
h := mpeg.Header(tc.bytes)
assert.Equal(t, int(tc.expSampleRate), int(h.SampleRate()))
})
}
@ -462,7 +463,7 @@ func TestLen(t *testing.T) {
for _, tc := range testCases {
t.Run(tc.name, func(t *testing.T) {
h := header(tc.bytes)
h := mpeg.Header(tc.bytes)
assert.Equal(t, tc.expLen, h.Len())
})
}