add tests, implement frame size

This commit is contained in:
Rob Watson 2021-01-27 18:09:38 +01:00
parent bbd3dd881e
commit 5c836c4f70
2 changed files with 152 additions and 36 deletions

88
main.go
View File

@ -12,9 +12,8 @@ const fname = "/home/rob/share/home-office/example.mp3"
type (
AudioVersionId int
LayerIndex int
header []byte
Layer int
header []byte
)
const (
@ -25,14 +24,14 @@ const (
)
const (
LayerIndexReserved LayerIndex = iota
LayerIndexIII
LayerIndexII
LayerIndexI
LayerReserved Layer = iota
LayerIII
LayerII
LayerI
)
var (
bitRates = [5][16]uint32{
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},
@ -40,22 +39,21 @@ var (
{0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, 0},
}
sampleRates = [4][4]uint32{
sampleRates = [4][4]int{
{11025, 12000, 8000, 0},
{0, 0, 0, 0},
{22050, 24000, 16000, 0},
{44100, 48000, 32000, 0},
}
samplesPerFrame = [4][4]uint32{
{0, 384, 1152, 576},
samplesPerFrame = [4][4]int{
{0, 576, 1152, 384},
{0, 0, 0, 0},
{384, 1152, 576},
{384, 1152, 1152},
{0, 576, 1152, 384},
{0, 1152, 1152, 384},
}
)
// TODO: tests
func (h header) HasSyncWord() bool {
return h[0] == 0xff && h[1]&0xe0 == 0xe0
}
@ -64,20 +62,42 @@ func (h header) AudioVersionId() AudioVersionId {
return AudioVersionId((h[1] >> 3) & 0x3)
}
func (h header) LayerIndex() LayerIndex {
return LayerIndex((h[1] >> 1) & 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) SampleRate() uint32 {
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 !h.HasSyncWord() {
return false
@ -85,27 +105,36 @@ func (h header) IsValid() bool {
if h.AudioVersionId() == AudioVersionReserved {
return false
}
if h.LayerIndex() == LayerIndexReserved {
if h.Layer() == LayerReserved {
return false
}
if h.BitRate() == 0 {
return false
}
if h.SampleRate() == 0 {
return false
}
return true
}
func (h header) BitRate() uint32 {
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.LayerIndex() {
case LayerIndexIII:
switch h.Layer() {
case LayerIII:
j = 2
case LayerIndexII:
case LayerII:
j = 1
case LayerIndexI:
case LayerI:
j = 0
default:
return 0
@ -113,10 +142,10 @@ func (h header) BitRate() uint32 {
case AudioVersionReserved:
return 0
case AudioVersionMPEG2, AudioVersionMPEG25:
switch h.LayerIndex() {
case LayerIndexIII, LayerIndexII:
switch h.Layer() {
case LayerIII, LayerII:
j = 4
case LayerIndexI:
case LayerI:
j = 3
default:
return 0
@ -145,10 +174,11 @@ func main() {
log.Fatal(err)
}
h := header(buf)
if h.IsValid() {
fmt.Printf("Got header: %08b, audio version: %d, layer index: %d, bitrate: %d\n", h, h.AudioVersionId(), h.LayerIndex(), h.BitRate())
if h := 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 {
fmt.Println("Discarding a byte")
bufreader.Discard(3)
}
i++

View File

@ -60,22 +60,32 @@ func TestAudioVersionId(t *testing.T) {
assert.Equal(t, AudioVersionMPEG25, h.AudioVersionId())
}
func TestLayerIndex(t *testing.T) {
func TestLayer(t *testing.T) {
bytes := []byte{0xff, 0xe0, 0, 0}
h := header(bytes)
assert.Equal(t, LayerIndexReserved, h.LayerIndex())
assert.Equal(t, LayerReserved, h.Layer())
bytes = []byte{0xff, 0xe2, 0, 0}
h = header(bytes)
assert.Equal(t, LayerIndexIII, h.LayerIndex())
assert.Equal(t, LayerIII, h.Layer())
bytes = []byte{0xff, 0xe4, 0, 0}
h = header(bytes)
assert.Equal(t, LayerIndexII, h.LayerIndex())
assert.Equal(t, LayerII, h.Layer())
bytes = []byte{0xff, 0xe6, 0, 0}
h = header(bytes)
assert.Equal(t, LayerIndexI, h.LayerIndex())
assert.Equal(t, LayerI, h.Layer())
}
func TestPaddingBytes(t *testing.T) {
bytes := []byte{0xff, 0xe0, 0x2, 0}
h := header(bytes)
assert.Equal(t, 1, h.PaddingBytes())
bytes = []byte{0xff, 0xe0, 0x0, 0}
h = header(bytes)
assert.Equal(t, 0, h.PaddingBytes())
}
func TestIsProtected(t *testing.T) {
@ -88,11 +98,87 @@ func TestIsProtected(t *testing.T) {
assert.False(t, h.IsProtected())
}
func TestSamplesPerFrame(t *testing.T) {
testCases := []struct {
name string
bytes []byte
expSamplesPerFrame int
}{
{
"MPEG1 LayerI",
[]byte{0xff, 0xfe, 0, 0},
384,
},
{
"MPEG1 LayerII",
[]byte{0xff, 0xfc, 0, 0},
1152,
},
{
"MPEG1 LayerIII",
[]byte{0xff, 0xfa, 0, 0},
1152,
},
{
"MPEG1 LayerReserved",
[]byte{0xff, 0xf8, 0, 0},
0,
},
{
"MPEG2 LayerI",
[]byte{0xff, 0xf6, 0, 0},
384,
},
{
"MPEG2 LayerII",
[]byte{0xff, 0xf4, 0, 0},
1152,
},
{
"MPEG2 LayerIII",
[]byte{0xff, 0xf2, 0, 0},
576,
},
{
"MPEG2 LayerReserved",
[]byte{0xff, 0xf0, 0, 0},
0,
},
{
"MPEG25 LayerI",
[]byte{0xff, 0xe6, 0, 0},
384,
},
{
"MPEG25 LayerII",
[]byte{0xff, 0xe4, 0, 0},
1152,
},
{
"MPEG25 LayerIII",
[]byte{0xff, 0xe2, 0, 0},
576,
},
{
"MPEG25 LayerReserved",
[]byte{0xff, 0xe0, 0, 0},
0,
},
}
for _, tc := range testCases {
t.Run(tc.name, func(t *testing.T) {
h := header(tc.bytes)
assert.Equal(t, tc.expSamplesPerFrame, h.SamplesPerFrame())
})
}
}
func TestBitRate(t *testing.T) {
testCases := []struct {
name string
bytes []byte
expBitRate uint32
expBitRate int
}{
{
"empty header",
@ -228,7 +314,7 @@ func TestSampleRate(t *testing.T) {
testCases := []struct {
name string
bytes []byte
expSampleRate uint32
expSampleRate int
}{
{
"MPEG1 44.1k",