private int GetXingHeaderOffset(MpegFrameHeader mpegHeader)
{
// TODO: mpegHeader.IsProtected
switch (mpegHeader.AudioVersion)
{
case AudioVersion.Mpeg1:
return mpegHeader.ChannelMode != ChannelMode.Mono ? 32 : 17;
case AudioVersion.Mpeg2:
case AudioVersion.Mpeg25:
return mpegHeader.ChannelMode != ChannelMode.Mono ? 17 : 9;
}
throw new NotSupportedException();
}
public MpegFileInfo(Stream stream)
: this()
{
MaxBitrate = int.MinValue;
MinBitrate = int.MaxValue;
if (stream.Length < 4)
return;
stream.Seek(0, SeekOrigin.Begin);
long expectedNextFrameOffset = 0;
long frameCount = 0;
long bitrateSum = 0;
while (stream.Position <= stream.Length)
{
var buffer = new byte[4];
var bytesRead = stream.Read(buffer, 0, 4);
if (bytesRead < 4)
break;
if (!MpegFrameHeader.IsValid(buffer))
{
if (stream.Position == stream.Length)
break;
stream.Seek(-3, SeekOrigin.Current);
if (frameCount == 0)
expectedNextFrameOffset = stream.Position;
// An invalid frame after the first 2 valid frames indicates false detection
if (frameCount <= 2)
{
_firstMpegFrameHeader = null;
_firstMpegFrameData = null;
MinBitrate = int.MaxValue;
MaxBitrate = int.MinValue;
frameCount = 0;
bitrateSum = 0;
}
continue;
}
if (frameCount > 0 && expectedNextFrameOffset != stream.Position - 4)
Errors.Add(new MisplacedFrameMpegError(expectedNextFrameOffset, stream.Position - 4, TimeSpan.FromSeconds(frameCount * _firstMpegFrameHeader.SamplesPerFrame / _firstMpegFrameHeader.SampleRate)));
var mpegHeader = new MpegFrameHeader(buffer);
var frameOffset = stream.Position - 4;
if (frameCount == 0)
{
_firstMpegFrameHeader = mpegHeader;
_firstMpegFrameData = new byte[mpegHeader.FrameSize];
stream.Read(_firstMpegFrameData, 0, _firstMpegFrameData.Length);
StartOffset = frameOffset;
}
if (mpegHeader.Bitrate < MinBitrate)
MinBitrate = mpegHeader.Bitrate;
if (mpegHeader.Bitrate > MaxBitrate)
MaxBitrate = mpegHeader.Bitrate;
bitrateSum += mpegHeader.Bitrate;
frameCount++;
expectedNextFrameOffset = frameOffset + mpegHeader.FrameSize;
if (expectedNextFrameOffset == stream.Length)
break;
if (expectedNextFrameOffset > stream.Length)
{
Errors.Add(new LastFrameTruncatedMpegError());
break;
}
stream.Seek(expectedNextFrameOffset, SeekOrigin.Begin);
Size = (int)(stream.Position - StartOffset);
}
if (frameCount > 0)
{
Bitrate = (int)(bitrateSum / frameCount);
Duration = TimeSpan.FromSeconds(frameCount * _firstMpegFrameHeader.SamplesPerFrame / _firstMpegFrameHeader.SampleRate);
HasXingHeader = ArrayHelper.CompareArray(_firstMpegFrameData.SubArray(GetXingHeaderOffset(_firstMpegFrameHeader), 4), XingSignature);
HasVbriHeader = ArrayHelper.CompareArray(_firstMpegFrameData.SubArray(32, 4), VbriSignature);
}
}
