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add ReadADTSHeader()

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This commit is contained in:
nareix 2016-03-29 23:12:26 +08:00
parent 3294a57e48
commit 02b80d86df
2 changed files with 58 additions and 7 deletions
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50
isom/isom.go
View File

@ -1,10 +1,10 @@
package isom
import (
"github.com/nareix/bits"
"io"
"bytes"
"fmt"
"github.com/nareix/bits"
"io"
"io/ioutil"
)
@ -78,6 +78,51 @@ var chanConfigTable = []int{
0, 1, 2, 3, 4, 5, 6, 8,
}
func ReadADTSHeader(data []byte) (objectType, sampleRateIndex, chanConfig, frameLength uint) {
br := &bits.Reader{R: bytes.NewReader(data)}
//Structure
//AAAAAAAA AAAABCCD EEFFFFGH HHIJKLMM MMMMMMMM MMMOOOOO OOOOOOPP (QQQQQQQQ QQQQQQQQ)
//Header consists of 7 or 9 bytes (without or with CRC).
//A 12 syncword 0xFFF, all bits must be 1
br.ReadBits(12)
//B 1 MPEG Version: 0 for MPEG-4, 1 for MPEG-2
br.ReadBits(1)
//C 2 Layer: always 0
br.ReadBits(2)
//D 1 protection absent, Warning, set to 1 if there is no CRC and 0 if there is CRC
br.ReadBits(1)
//E 2 profile, the MPEG-4 Audio Object Type minus 1
objectType, _ = br.ReadBits(2)
objectType++
//F 4 MPEG-4 Sampling Frequency Index (15 is forbidden)
sampleRateIndex, _ = br.ReadBits(4)
//G 1 private bit, guaranteed never to be used by MPEG, set to 0 when encoding, ignore when decoding
br.ReadBits(1)
//H 3 MPEG-4 Channel Configuration (in the case of 0, the channel configuration is sent via an inband PCE)
chanConfig, _ = br.ReadBits(3)
//I 1 originality, set to 0 when encoding, ignore when decoding
br.ReadBits(1)
//J 1 home, set to 0 when encoding, ignore when decoding
br.ReadBits(1)
//K 1 copyrighted id bit, the next bit of a centrally registered copyright identifier, set to 0 when encoding, ignore when decoding
br.ReadBits(1)
//L 1 copyright id start, signals that this frame's copyright id bit is the first bit of the copyright id, set to 0 when encoding, ignore when decoding
br.ReadBits(1)
//M 13 frame length, this value must include 7 or 9 bytes of header length: FrameLength = (ProtectionAbsent == 1 ? 7 : 9) + size(AACFrame)
frameLength, _ = br.ReadBits(13)
//O 11 Buffer fullness
br.ReadBits(11)
//P 2 Number of AAC frames (RDBs) in ADTS frame minus 1, for maximum compatibility always use 1 AAC frame per ADTS frame
br.ReadBits(2)
//Q 16 CRC if protection absent is 0
return
}
func readObjectType(r *bits.Reader) (objectType uint, err error) {
if objectType, err = r.ReadBits(5); err != nil {
return
@ -419,4 +464,3 @@ func WriteElemStreamDescAAC(w io.Writer, config MPEG4AudioConfig) (err error) {
return
}

7
isom/isom_test.go
View File

@ -38,5 +38,12 @@ func TestReadElemStreamDesc(t *testing.T) {
t.Error(err)
}
t.Logf("decConfig=%x", decConfig)
//00000000 ff f1 50 80 04 3f fc de 04 00 00 6c 69 62 66 61 |..P..?.....libfa|
//00000010 61 63 20 31 2e 32 38 00 00 42 40 93 20 04 32 00 |ac 1.28..B@. .2.|
//00000020 47 ff f1 50 80 05 1f fc 21 42 fe ed b2 5c a8 00 |G..P....!B...\..|
data, _ = hex.DecodeString("fff15080043ffcde040000")
objectType, sampleRateIndex, chanConfig, frameLength := ReadADTSHeader(data)
t.Logf("objectType=%d sampleRateIndex=%d chanConfig=%d frameLength=%d", objectType, sampleRateIndex, chanConfig, frameLength)
}