private static async Task <Tuple <List <Frame>, BitrateType, TimeSpan, UInt32> > CollectSamplesAsync(IBinaryStream stream, UInt32 streamLength, UInt32?amount)
{
var samples = new List <Frame>();
var bitrateType = BitrateType.Constant;
var duration = new TimeSpan();
var bitrateSum = 0U;
var originalPosition = stream.Position;
while (stream.Position + 20 < streamLength)
{
if (amount.HasValue && (samples.Count == amount.Value))
{
break;
}
var possibleFrameHeader = await stream.PeekUInt32Async(ByteOrder.BigEndian).ConfigureAwait(false);
if ((possibleFrameHeader & 0xFFFE0000) == 0xFFFA0000)
{
var bitrate = Frame.GetBitrate(possibleFrameHeader);
var frequency = Frame.GetFrequency(possibleFrameHeader);
var padding = Frame.GetPadding(possibleFrameHeader);
var version = Frame.GetVersion(possibleFrameHeader);
var layer = Frame.GetLayer(possibleFrameHeader);
if ((bitrate != 0) && (frequency != 0))
{
var frame = new Frame(stream.Position, version, layer, bitrate, frequency, padding);
if (samples.Count == 0)
{
var firstFrameContent = await stream.ReadAsync(frame.Length).ConfigureAwait(false);
bitrateType = firstFrameContent.IndexOf("Xing").HasValue ? BitrateType.Variable : BitrateType.Constant;
}
else
{
stream.Position += frame.Length;
duration += frame.Duration;
bitrateSum += frame.Bitrate;
}
samples.Add(frame);
continue;
}
}
// this situation means that we've read some samples and haven't found valid sample right after the last valid sample
// and it means that the file in wrong format, corrupted or we've found all samples.
if (samples.Count > 0)
{
break;
}
stream.Position += 1;
if (stream.Position - originalPosition > 1024)
{
break;
}
}
return(new Tuple <List <Frame>, BitrateType, TimeSpan, UInt32>(samples, bitrateType, duration, (samples.Count > 0) ? (UInt32)(bitrateSum / samples.Count) : 0));
}
