我试图将2个AAC文件组合成一个，我发现在AAC文件中 - 头元素存在直到FF8字节，然后接下来的4个字节包含AAC数据的长度。我试图维护1个头数组，添加2个AAC文件的大小，然后依次添加这两个文件的数据缓冲区。
结果文件仅播放第一个AAC文件。这是代码段。
FileInputStream fs = new FileInputStream("./res/after.aac");
dis = new DataInputStream(fs);
headerData = new byte[0xFF8];
dis.read(headerData);
int lengthTotal = dis.readInt();
System.out.println("Length of After == "+lengthTotal);
dis.readInt();
data = new byte[dis.available()];
dis.readFully(data);
dis.close();
dis = null;
fs.close();
fs = null;
fs = new FileInputStream("./res/continue.aac");
dis = new DataInputStream(fs);
dis.skipBytes(0xFF8);
int length = dis.readInt();
System.out.println("Length of Ahead == "+length);
lengthTotal = lengthTotal + length -8;
System.out.println("Total Length== "+lengthTotal);
dis.readInt();
newData = new byte[dis.available()];
dis.read(newData);
FileOutputStream fos = new FileOutputStream("./res/combine.aac");
DataOutputStream dos = new DataOutputStream(fos);
dos.write(headerData);
dos.writeInt(lengthTotal);
dos.writeBytes("mdat");
dos.write(data);
dos.write(newData);
我知道第56个字节中有关于AAC文件的持续时间的信息，但我无法弄明白。有人可以帮助我吗？
答案 0 :(得分：1)
好吧，我不能告诉你你做错了什么。但我可以告诉你如何做你想做的事。
首先创建一个通用助手函数：
public static class General {
public static void CopyBytes(byte[] dst, int dstOffset, byte[] src) {
Buffer.BlockCopy(src, 0, dst, dstOffset, src.Length);
}
}
public static class BitHelper {
public static int Read(ref ulong x, int length) {
int r = (int)(x >> (64 - length));
x <<= length;
return r;
}
public static int Read(byte[] bytes, ref int offset, int length) {
int startByte = offset / 8;
int endByte = (offset + length - 1) / 8;
int skipBits = offset % 8;
ulong bits = 0;
for (int i = 0; i <= Math.Min(endByte - startByte, 7); i++) {
bits |= (ulong)bytes[startByte + i] << (56 - (i * 8));
}
if (skipBits != 0) Read(ref bits, skipBits);
offset += length;
return Read(ref bits, length);
}
public static void Write(ref ulong x, int length, int value) {
ulong mask = 0xFFFFFFFFFFFFFFFF >> (64 - length);
x = (x << length) | ((ulong)value & mask);
}
public static byte[] CopyBlock(byte[] bytes, int offset, int length) {
int startByte = offset / 8;
int endByte = (offset + length - 1) / 8;
int shiftA = offset % 8;
int shiftB = 8 - shiftA;
byte[] dst = new byte[(length + 7) / 8];
if (shiftA == 0) {
Buffer.BlockCopy(bytes, startByte, dst, 0, dst.Length);
}
else {
int i;
for (i = 0; i < endByte - startByte; i++) {
dst[i] = (byte)((bytes[startByte + i] << shiftA) | (bytes[startByte + i + 1] >> shiftB));
}
if (i < dst.Length) {
dst[i] = (byte)(bytes[startByte + i] << shiftA);
}
}
dst[dst.Length - 1] &= (byte)(0xFF << ((dst.Length * 8) - length));
return dst;
}
}
public static class BitConverterBE {
public static ulong ToUInt64(byte[] value, int startIndex) {
return
((ulong)value[startIndex ] << 56) |
((ulong)value[startIndex + 1] << 48) |
((ulong)value[startIndex + 2] << 40) |
((ulong)value[startIndex + 3] << 32) |
((ulong)value[startIndex + 4] << 24) |
((ulong)value[startIndex + 5] << 16) |
((ulong)value[startIndex + 6] << 8) |
((ulong)value[startIndex + 7] );
}
public static uint ToUInt32(byte[] value, int startIndex) {
return
((uint)value[startIndex ] << 24) |
((uint)value[startIndex + 1] << 16) |
((uint)value[startIndex + 2] << 8) |
((uint)value[startIndex + 3] );
}
public static ushort ToUInt16(byte[] value, int startIndex) {
return (ushort)(
(value[startIndex ] << 8) |
(value[startIndex + 1] ));
}
public static byte[] GetBytes(ulong value) {
byte[] buff = new byte[8];
buff[0] = (byte)(value >> 56);
buff[1] = (byte)(value >> 48);
buff[2] = (byte)(value >> 40);
buff[3] = (byte)(value >> 32);
buff[4] = (byte)(value >> 24);
buff[5] = (byte)(value >> 16);
buff[6] = (byte)(value >> 8);
buff[7] = (byte)(value );
return buff;
}
public static byte[] GetBytes(uint value) {
byte[] buff = new byte[4];
buff[0] = (byte)(value >> 24);
buff[1] = (byte)(value >> 16);
buff[2] = (byte)(value >> 8);
buff[3] = (byte)(value );
return buff;
}
public static byte[] GetBytes(ushort value) {
byte[] buff = new byte[2];
buff[0] = (byte)(value >> 8);
buff[1] = (byte)(value );
return buff;
}
}
public static class BitConverterLE {
public static byte[] GetBytes(ulong value) {
byte[] buff = new byte[8];
buff[0] = (byte)(value );
buff[1] = (byte)(value >> 8);
buff[2] = (byte)(value >> 16);
buff[3] = (byte)(value >> 24);
buff[4] = (byte)(value >> 32);
buff[5] = (byte)(value >> 40);
buff[6] = (byte)(value >> 48);
buff[7] = (byte)(value >> 56);
return buff;
}
public static byte[] GetBytes(uint value) {
byte[] buff = new byte[4];
buff[0] = (byte)(value );
buff[1] = (byte)(value >> 8);
buff[2] = (byte)(value >> 16);
buff[3] = (byte)(value >> 24);
return buff;
}
public static byte[] GetBytes(ushort value) {
byte[] buff = new byte[2];
buff[0] = (byte)(value );
buff[1] = (byte)(value >> 8);
return buff;
}
}
现在实现音频助手类和接口：
interface IAudioWriter
{
void WriteChunk(byte[] chunk, uint timeStamp);
void Finish();
string Path { get; }
}
class AACWriter : IAudioWriter
{
string _path;
FileStream _fs;
int _aacProfile;
int _sampleRateIndex;
int _channelConfig;
public AACWriter(string path) {
_path = path;
_fs = new FileStream(path, FileMode.Create, FileAccess.Write, FileShare.Read, 65536);
}
public void WriteChunk(byte[] chunk, uint timeStamp)
{
if (chunk.Length < 1) return;
if (chunk[0] == 0) { // Header
if (chunk.Length < 3) return;
ulong bits = (ulong)BitConverterBE.ToUInt16(chunk, 1) << 48;
_aacProfile = BitHelper.Read(ref bits, 5) - 1;
_sampleRateIndex = BitHelper.Read(ref bits, 4);
_channelConfig = BitHelper.Read(ref bits, 4);
if ((_aacProfile < 0) || (_aacProfile > 3))
throw new Exception("Unsupported AAC profile.");
if (_sampleRateIndex > 12)
throw new Exception("Invalid AAC sample rate index.");
if (_channelConfig > 6)
throw new Exception("Invalid AAC channel configuration.");
}
else { // Audio data
int dataSize = chunk.Length - 1;
ulong bits = 0;
// Reference: WriteADTSHeader from FAAC's bitstream.c
BitHelper.Write(ref bits, 12, 0xFFF);
BitHelper.Write(ref bits, 1, 0);
BitHelper.Write(ref bits, 2, 0);
BitHelper.Write(ref bits, 1, 1);
BitHelper.Write(ref bits, 2, _aacProfile);
BitHelper.Write(ref bits, 4, _sampleRateIndex);
BitHelper.Write(ref bits, 1, 0);
BitHelper.Write(ref bits, 3, _channelConfig);
BitHelper.Write(ref bits, 1, 0);
BitHelper.Write(ref bits, 1, 0);
BitHelper.Write(ref bits, 1, 0);
BitHelper.Write(ref bits, 1, 0);
BitHelper.Write(ref bits, 13, 7 + dataSize);
BitHelper.Write(ref bits, 11, 0x7FF);
BitHelper.Write(ref bits, 2, 0);
_fs.Write(BitConverterBE.GetBytes(bits), 1, 7);
_fs.Write(chunk, 1, dataSize);
}
}
public void Finish() {
_fs.Close();
}
public string Path {
get {
return _path;
}
}
}
现在您需要自己做的是，从第一个AAC文件中逐个读取块并写入它们，之后，从第二个AAC文件中逐个读取块并将它们附加到中间文件。
注意，上面的代码是C＃，因此您必须使用换行来模拟C＃的ref效果，只需替换：
ref Type variable_name
使用：
_<Type> variable_name
答案 1 :(得分：1)