/// <summary>
/// Decode the standard format.
/// Copied from: "http://en.wikipedia.org/wiki/ADX_(file_format)"
/// </summary>
/// <param name="buffer">buffer is where the decoded samples will be put</param>
/// <param name="samples_needed">samples_needed states how many sample 'sets' (one sample from every channel) need to be decoded to fill the buffer</param>
/// <param name="looping_enabled">looping_enabled is a boolean flag to control use of the built-in loop</param>
/// <returns>Returns the number of sample 'sets' in the buffer that could not be filled (EOS)</returns>
public override byte[] Decode(byte[] encoded, bool looping_enabled)
{
BitReader bit_reader = new BitReader(encoded, true);
List<byte> bufferOut = new List<byte>();
Initialize_Decode();
// Param:
uint samples_needed = adx_header.total_samples;
uint samples_per_block = (uint)((adx_header.block_size - 2) * 8 / adx_header.sample_bitdepth);
short[] scale = new short[adx_header.channel_count];
if (looping_enabled && adx_header.loop_enabled == 0)
looping_enabled = false;
if (looping_enabled) // Mine
sample_index = adx_header.loop_begin_sample_index;
// Loop until the requested number of samples are decoded, or the end of file is reached
while (samples_needed > 0 && sample_index < adx_header.total_samples)
{
// Calculate the number of samples that are left to be decoded in the current block
uint sample_offset = sample_index % samples_per_block;
uint samples_can_get = samples_per_block - sample_offset;
// Clamp the samples we can get during this run if they won't fit in the buffer
if (samples_can_get > samples_needed)
samples_can_get = samples_needed;
// Clamp the number of samples to be acquired if the stream isn't long enough or the loop trigger is nearby
if (looping_enabled && sample_index + samples_can_get > adx_header.loop_end_sample_index)
samples_can_get = adx_header.loop_end_sample_index - sample_index;
else if (sample_index + samples_can_get > adx_header.total_samples)
samples_can_get = adx_header.total_samples - sample_index;
// Calculate the bit address of the start of the frame that sample_index resides in and record that location
ulong started_at = (ulong)(adx_header.copyright_offset + 4 +
sample_index / samples_per_block * adx_header.block_size * adx_header.channel_count) * 8;
// Read the scale values from the start of each block in this frame
for (uint i = 0; i < adx_header.channel_count; ++i)
{
bit_reader.Seek((int)(started_at + adx_header.block_size * i * 8));
scale[i] = bit_reader.Read_Short();
}
// Pre-calculate the stop value for sample_offset
uint sample_endoffset = sample_offset + samples_can_get;
// Save the bitstream address of the first sample immediately after the scale in the first block of the frame
started_at += 16;
while (sample_offset < sample_endoffset)
{
for (uint i = 0; i < adx_header.channel_count; ++i)
{
// Predict the next sample
double sample_prediction = coefficient[0] * past_samples[i * 2 + 0] + coefficient[1] * past_samples[i * 2 + 1];
// Seek to the sample offset, read and sign extend it to a 32bit integer
bit_reader.Seek((int)((int)started_at + adx_header.sample_bitdepth * sample_offset + adx_header.block_size * 8 * i));
int sample_error = 0;
if (adx_header.sample_bitdepth == 4)
sample_error = bit_reader.Read_4Bits();
// Scale the error correction value
sample_error *= scale[i];
// Calculate the sample by combining the prediction with the error correction
int sample = sample_error + (int)sample_prediction;
// Update the past samples with the newer sample
past_samples[i * 2 + 1] = past_samples[i * 2 + 0];
past_samples[i * 2 + 0] = sample;
// Clamp the decoded sample to the valid range for a 16bit integer
if (sample > 32767)
sample = 32767;
else if (sample < -32768)
sample = -32768;
bufferOut.AddRange(BitConverter.GetBytes((short)sample));
}
++sample_offset; // We've decoded one sample from every block, advance block offset by 1
++sample_index; // This also means we're one sample further into the stream
--samples_needed; // And so there is one less set of samples that need to be decoded
}
// Check if we hit the loop end marker, if we did we need to jump to the loop start
if (looping_enabled && sample_index == adx_header.loop_end_sample_index)
//sample_index = adx_header.loop_begin_sample_index;
break;
}
//return samples_needed;
return bufferOut.ToArray();
}
