Callback trouble!!

From: Erik Brännlund (erik.brannlund_nospam__at_epl.ericsson.se)
Date: 06/22/04 

Date: Tue, 22 Jun 2004 14:27:55 GMT

Hi!

I have made an application showing TV from my DVB card. I also try to extract
the subtitling. I do this by making a callback function and telling th
directshow filter what PID I want and the callback function.

Callback function

Procedure Test(pTsp : PByteArray);safecall;
begin
  Form1.ProcessSubtitle(pTsp);
  Form1.Panel1.Caption := 'End';
end;

Specifiyng callback
  m_pfSource.DvbSource.AddPidFilter(@Test, 1015);

Class to extract bits from stream
Constructor TBitExtractor.Create;
begin
  BitPos := 0;
end;

Function TBitExtractor.GetBits(I : Integer; Data : PByteArray):LongWord;
var
  Byp, Bip : Integer;
begin
  Result := 0;
  While I > 0 do
  begin
    Result := Result shl 1;
    Byp := BitPos div 8;
    Bip := BitPos mod 8;
    Result := Result or ((Data^[Byp] shr (7 - Bip)) and 1);
    BitPos := BitPos + 1;
    Dec(I);
  end;
end;

Function TBitExtractor.CheckBits(I : Integer; Data : PByteArray):LongWord;
var
  Byp, Bip : Integer;
  TmpPos : LongInt;
begin
  TmpPos := BitPos;
  Result := 0;
  While I < 0 do
  begin
    Result := Result shl 1;
    Byp := TmpPos div 8;
    Bip := TmpPos mod 8;
    Result := Result or (Data^[Byp] shr (7 - Bip));
    TmpPos := TmpPos + 1;
  end;
end;

Subtitle extraction code or at least the beginning of it
Procedure TForm1.ProcessSubtitle(pTsp : PByteArray);
var
  I : Integer;
  Be : TBitExtractor;
  ts : TSPacket;
begin
  Be := TBitExtractor.Create;
  Form1.Panel1.Caption := 'Called 1'; // This updates the Panel
  ts.Sync := Be.GetBits(8, pTsp);
  Form1.Panel1.Caption := 'Called 2'; //This doesn't eupdate the panel
  ts.trans_error_ind := Be.GetBits(1, pTsp);
  ts.payload_start := Be.GetBits(1, pTsp);
  ts.transportprio := Be.GetBits(1, pTsp);
  ts.PID := Be.GetBits(13, pTsp);
  ts.ts_scramble_control := Be.GetBits(2, pTsp);
  ts.adaption_control := Be.GetBits(2, pTsp);
  ts.cont_count := Be.GetBits(4, pTsp);

  Be.Free;
end;

I declared the functions as (var pTsp : Array of Byte) and the stream was
decoded but the prg crashed upon exit from "Test". Now the application don't
crash, at least not immediately, but the strem dont get decoded.

Any suggestions?

P.S
As long as I skip this subtitle stream the "TV" works just fine.
D.S

/Erik