4.1. Подпрограмма mpeg frame header data

function TMPEGaudio.ReadFromFile(const FileName: string): Boolean;

var

SourceFile: file;

Data: array [1..MAX_MPEG_FRAME_LENGTH * 2] of Byte;

Transferred: Integer;

begin

Result := false;

{ At first search for tags, then search for a MPEG frame and VBR data }

if (FID3v2.ReadFromFile(FileName)) and (FID3v1.ReadFromFile(FileName)) then

try

{ Open file, read first block of data and search for a frame }

AssignFile(SourceFile, FileName);

FileMode := 0;

Reset(SourceFile, 1);

FFileLength := FileSize(SourceFile);

Seek(SourceFile, FID3v2.Size);

BlockRead(SourceFile, Data, SizeOf(Data), Transferred);

FFrame := FindFrame(Data, FVBR);

{ Try to search in the middle if no frame at the beginning found }

if (not FFrame.Found) and (Transferred = SizeOf(Data)) then

begin

Seek(SourceFile, (FFileLength - FID3v2.Size) div 2);

BlockRead(SourceFile, Data, SizeOf(Data), Transferred);

FFrame := FindFrame(Data, FVBR);

end;

{ Search for vendor ID at the end if CBR encoded }

if (FFrame.Found) and (not FVBR.Found) then

begin

if not FID3v1.Exists then Seek(SourceFile, FFileLength - SizeOf(Data))

else Seek(SourceFile, FFileLength - SizeOf(Data) - 128);

BlockRead(SourceFile, Data, SizeOf(Data), Transferred);

FVendorID := FindVendorID(Data, FFrame.Size * 5);

end;

CloseFile(SourceFile);

Result := true;

except

end;

4.2. Подпрограмма GetFrameLength

function GetFrameLength(const Frame: FrameData): Word;

var

Coefficient, BitRate, SampleRate, Padding: Word;

begin

{ Calculate MPEG frame length }

Coefficient := GetCoefficient(Frame);

BitRate := GetBitRate(Frame);

SampleRate := GetSampleRate(Frame);

Padding := GetPadding(Frame);

Result := Trunc(Coefficient * BitRate * 1000 / SampleRate) + Padding;

end;

4.3. Подпрограмма FindFrame

function FindFrame(const Data: array of Byte; var VBR: VBRData): FrameData;

var

HeaderData: array [1..4] of Byte;

Iterator: Integer;

begin

{ Search for valid frame }

FillChar(Result, SizeOf(Result), 0);

Move(Data, HeaderData, SizeOf(HeaderData));

for Iterator := 0 to SizeOf(Data) - MAX_MPEG_FRAME_LENGTH do

begin

{ Decode data if frame header found }

if IsFrameHeader(HeaderData) then

begin

DecodeHeader(HeaderData, Result);

{ Check for next frame and try to find VBR header }

if ValidFrameAt(Iterator + GetFrameLength(Result), Data) then

begin

Result.Found := true;

Result.Position := Iterator;

Result.Size := GetFrameLength(Result);

Result.Xing := IsXing(Iterator + SizeOf(HeaderData), Data);

VBR := FindVBR(Iterator + GetVBRDeviation(Result), Data);

break;

end;

end;

{ Prepare next data block }

HeaderData[1] := HeaderData[2];

HeaderData[2] := HeaderData[3];

HeaderData[3] := HeaderData[4];

HeaderData[4] := Data[Iterator + SizeOf(HeaderData)];

end;

end;