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);
}
