import com.google.android.exoplayer2.C; //导入方法依赖的package包/类

/**

* Peeks and returns a {@code WavHeader}.

*

* @param input Input stream to peek the WAV header from.

* @throws ParserException If the input file is an incorrect RIFF WAV.

* @throws IOException If peeking from the input fails.

* @throws InterruptedException If interrupted while peeking from input.

* @return A new {@code WavHeader} peeked from {@code input}, or null if the input is not a

* supported WAV format.

*/

public static WavHeader peek(ExtractorInput input) throws IOException, InterruptedException {

Assertions.checkNotNull(input);

// Allocate a scratch buffer large enough to store the format chunk.

ParsableByteArray scratch = new ParsableByteArray(16);

// Attempt to read the RIFF chunk.

ChunkHeader chunkHeader = ChunkHeader.peek(input, scratch);

if (chunkHeader.id != Util.getIntegerCodeForString("RIFF")) {

return null;

}

input.peekFully(scratch.data, 0, 4);

scratch.setPosition(0);

int riffFormat = scratch.readInt();

if (riffFormat != Util.getIntegerCodeForString("WAVE")) {

Log.e(TAG, "Unsupported RIFF format: " + riffFormat);

return null;

}

// Skip chunks until we find the format chunk.

chunkHeader = ChunkHeader.peek(input, scratch);

while (chunkHeader.id != Util.getIntegerCodeForString("fmt ")) {

input.advancePeekPosition((int) chunkHeader.size);

chunkHeader = ChunkHeader.peek(input, scratch);

}

Assertions.checkState(chunkHeader.size >= 16);

input.peekFully(scratch.data, 0, 16);

scratch.setPosition(0);

int type = scratch.readLittleEndianUnsignedShort();

int numChannels = scratch.readLittleEndianUnsignedShort();

int sampleRateHz = scratch.readLittleEndianUnsignedIntToInt();

int averageBytesPerSecond = scratch.readLittleEndianUnsignedIntToInt();

int blockAlignment = scratch.readLittleEndianUnsignedShort();

int bitsPerSample = scratch.readLittleEndianUnsignedShort();

int expectedBlockAlignment = numChannels * bitsPerSample / 8;

if (blockAlignment != expectedBlockAlignment) {

throw new ParserException("Expected block alignment: " + expectedBlockAlignment + "; got: "

+ blockAlignment);

}

@C.PcmEncoding int encoding = Util.getPcmEncoding(bitsPerSample);

if (encoding == C.ENCODING_INVALID) {

Log.e(TAG, "Unsupported WAV bit depth: " + bitsPerSample);

return null;

}

if (type != TYPE_PCM && type != TYPE_WAVE_FORMAT_EXTENSIBLE) {

Log.e(TAG, "Unsupported WAV format type: " + type);

return null;

}

// If present, skip extensionSize, validBitsPerSample, channelMask, subFormatGuid, ...

input.advancePeekPosition((int) chunkHeader.size - 16);

return new WavHeader(numChannels, sampleRateHz, averageBytesPerSecond, blockAlignment,

bitsPerSample, encoding);

}