All geek questions in one place

Combining 2 AAC files using Java

I try to merge two AAC files into one, I found out that in AAC files - the header element is present before the FF8 byte, and then the next 4 bytes contain the length of the AAC data. I tried to save 1 array of headers, add the size of the two AAC files, and then add the data buffer of the two files one by one.

As a result, the file played only the first AAC file. Here is a snippet of code.

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);

I know that there is information about the duration of the AAC file in the 56th byte, but I can not understand it. Can anyone help me here?

+6
source share
2 answers

Well, I can’t tell you what you are doing wrong. But I can tell you how to do what you want to do.

First create common helper functions:

  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; } }

Now we implement the sound assistant class and interface:

  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 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; } } }

Now what you need to do yourself is to read the fragments one by one from the first AAC file and write them, after that, read one fragment from the second AAC file and add them to the intermediate file.

Please note that the code above is C #, so you will have to use wrapping to simulate the C # ref effect by simply replacing:

 ref Type variable_name

from:

 _<Type> variable_name
+1
source

I would advise you to take a look at how aac files are parsed in the jaad library, it is especially interesting that ADTS handles the code here and the ADIF header here .

+1
source

Source: https://habr.com/ru/post/926902/

More articles:


All Articles