/**
* Returns the AC-3 frame size in bytes given {@code data} containing the frame header starting
* from the sync word.
*
* @param data Data to parse, positioned at the start of the syncword.
* @return The frame size parsed from data in the header.
*/
public static int parseFrameSize(ParsableBitArray data) {
// Skip syncword and crc1.
data.skipBits(4 * 8);
int fscod = data.readBits(2);
int frmsizecod = data.readBits(6);
int sampleRate = SAMPLE_RATES[fscod];
int bitrate = BITRATES[frmsizecod / 2];
if (sampleRate == 32000) {
return 6 * bitrate;
} else if (sampleRate == 44100) {
return 2 * (FRMSIZECOD_TO_FRAME_SIZE_44_1[frmsizecod / 2] + (frmsizecod % 2));
} else { // sampleRate == 48000
return 4 * bitrate;
}
}
/**
* Returns the AC-3 format given {@code data} containing the frame header starting from the sync
* word.
*
* @param data Data to parse, positioned at the start of the syncword.
* @return AC-3 format parsed from data in the header.
*/
public static MediaFormat parseFrameAc3Format(ParsableBitArray data) {
// Skip syncword and crc1.
data.skipBits(4 * 8);
int fscod = data.readBits(2);
data.skipBits(14); // frmsizecod(6) + bsid (5 bits) + bsmod (3 bits)
int acmod = data.readBits(3);
if ((acmod & 0x01) != 0 && acmod != 1) {
data.skipBits(2); // cmixlev
}
if ((acmod & 0x04) != 0) {
data.skipBits(2); // surmixlev
}
if (acmod == 0x02) {
data.skipBits(2); // dsurmod
}
boolean lfeon = data.readBit();
return MediaFormat.createAudioFormat(
MimeTypes.AUDIO_AC3,
MediaFormat.NO_VALUE,
CHANNEL_COUNTS[acmod] + (lfeon ? 1 : 0),
SAMPLE_RATES[fscod],
null);
}