我正在android上编辑mp4，使用mediaextractor获取音频和视频曲目，然后使用mediamuxer创建一个新文件。它工作得很好。我可以在电话上播放新的mp4（和其他播放器），但无法在网络上传输文件。当我停止mediamuxer时，它会生成一条日志消息
“MP4文件将无法进行流式处理。”
我查看了底层的本机代码（mpeg4writer.cpp），发现编写器在计算所需的moov框大小时遇到了问题。它试图使用一些启发式的猜测，如果一个比特率没有作为一个参数提供给编写器。问题是mediamuxer不提供设置mpeg4writer参数的功能。我是遗漏了什么，还是一直在寻找生成文件（或头）的其他方法？谢谢。
最佳答案
在mpeg4writer.cpp中：
// The default MIN_MOOV_BOX_SIZE is set to 0.6% x 1MB / 2,
// where 1MB is the common file size limit for MMS application.
// The default MAX _MOOV_BOX_SIZE value is based on about 3
// minute video recording with a bit rate about 3 Mbps, because
// statistics also show that most of the video captured are going
// to be less than 3 minutes.
对于如何使用mediamuxer，这是一个错误的假设。我们正在录制最高15秒的高分辨率视频，而最小的moov盒太小了。因此，为了使文件可流化，我必须重写文件以在mdat之前移动moov头并修补一些偏移量。这是我的密码。不太好。错误路径处理不正确，并且它会对框的顺序进行假设。
public void fastPlay(String srcFile, String dstFile) {
RandomAccessFile inFile = null;
FileOutputStream outFile = null;
try {
inFile = new RandomAccessFile(new File(srcFile), "r");
outFile = new FileOutputStream(new File(dstFile));
int moovPos = 0;
int mdatPos = 0;
int moovSize = 0;
int mdatSize = 0;
byte[] boxSizeBuf = new byte[4];
byte[] pathBuf = new byte[4];
int boxSize;
int dataSize;
int bytesRead;
int totalBytesRead = 0;
int bytesWritten = 0;
// First find the location and size of the moov and mdat boxes
while (true) {
try {
boxSize = inFile.readInt();
bytesRead = inFile.read(pathBuf);
if (bytesRead != 4) {
Log.e(TAG, "Unexpected bytes read (path) " + bytesRead);
break;
}
String pathRead = new String(pathBuf, "UTF-8");
dataSize = boxSize - 8;
totalBytesRead += 8;
if (pathRead.equals("moov")) {
moovPos = totalBytesRead - 8;
moovSize = boxSize;
} else if (pathRead.equals("mdat")) {
mdatPos = totalBytesRead - 8;
mdatSize = boxSize;
}
totalBytesRead += inFile.skipBytes(dataSize);
} catch (IOException e) {
break;
}
}
// Read the moov box into a buffer. This has to be patched up. Ug.
inFile.seek(moovPos);
byte[] moovBoxBuf = new byte[moovSize]; // This shouldn't be too big.
bytesRead = inFile.read(moovBoxBuf);
if (bytesRead != moovSize) {
Log.e(TAG, "Couldn't read full moov box");
}
// Now locate the stco boxes (chunk offset box) inside the moov box and patch
// them up. This ain't purdy.
int pos = 0;
while (pos < moovBoxBuf.length - 4) {
if (moovBoxBuf[pos] == 0x73 && moovBoxBuf[pos + 1] == 0x74 &&
moovBoxBuf[pos + 2] == 0x63 && moovBoxBuf[pos + 3] == 0x6f) {
int stcoPos = pos - 4;
int stcoSize = byteArrayToInt(moovBoxBuf, stcoPos);
patchStco(moovBoxBuf, stcoSize, stcoPos, moovSize);
}
pos++;
}
inFile.seek(0);
byte[] buf = new byte[(int) mdatPos];
// Write out everything before mdat
inFile.read(buf);
outFile.write(buf);
// Write moov
outFile.write(moovBoxBuf, 0, moovSize);
// Write out mdat
inFile.seek(mdatPos);
bytesWritten = 0;
while (bytesWritten < mdatSize) {
int bytesRemaining = (int) mdatSize - bytesWritten;
int bytesToRead = buf.length;
if (bytesRemaining < bytesToRead) bytesToRead = bytesRemaining;
bytesRead = inFile.read(buf, 0, bytesToRead);
if (bytesRead > 0) {
outFile.write(buf, 0, bytesRead);
bytesWritten += bytesRead;
} else {
break;
}
}
} catch (IOException e) {
Log.e(TAG, e.getMessage());
} finally {
try {
if (outFile != null) outFile.close();
if (inFile != null) inFile.close();
} catch (IOException e) {}
}
}
private void patchStco(byte[] buf, int size, int pos, int moovSize) {
Log.e(TAG, "stco " + pos + " size " + size);
// We are inserting the moov box before the mdat box so all of
// offsets in the stco box need to be increased by the size of the moov box. The stco
// box is variable in length. 4 byte size, 4 byte path, 4 byte version, 4 byte flags
// followed by a variable number of chunk offsets. So subtract off 16 from size then
// divide result by 4 to get the number of chunk offsets to patch up.
int chunkOffsetCount = (size - 16) / 4;
int chunkPos = pos + 16;
for (int i = 0; i < chunkOffsetCount; i++) {
int chunkOffset = byteArrayToInt(buf, chunkPos);
int newChunkOffset = chunkOffset + moovSize;
intToByteArray(newChunkOffset, buf, chunkPos);
chunkPos += 4;
}
}
public static int byteArrayToInt(byte[] b, int offset)
{
return b[offset + 3] & 0xFF |
(b[offset + 2] & 0xFF) << 8 |
(b[offset + 1] & 0xFF) << 16 |
(b[offset] & 0xFF) << 24;
}
public void intToByteArray(int a, byte[] buf, int offset)
{
buf[offset] = (byte) ((a >> 24) & 0xFF);
buf[offset + 1] = (byte) ((a >> 16) & 0xFF);
buf[offset + 2] = (byte) ((a >> 8) & 0xFF);
buf[offset + 3] = (byte) (a & 0xFF);
}