how to calculate the Framerate and Timecode during screen capturing?

Question

Delphi 6 project

I have searched google pretty thorough but am not finding the answers to my delima. basically i want to have the timecode and videos framerate of a current screen capture session showing in my app, in the statusbar or label. i also need this with respect to syncing the captures to the framerate of the sofware player playing the video, otherwise i get a lot of duplicate or missed frames. the videos are 29.970 and 23.976 fps. So i need to be able to configure for both, somehow.

Currently, I can screen capture from tv cards and software video players like, vlc, ffplay, mplayer, virtualdub, etc.

i'm not sure how to implement the necessary routines into mine, let alone where. i've been reading a lot about the following items below but they are all over my head though i did make many attempts at it:

1. timer1 control -- setting interval to 34 is not exact, it duplicates or misses frames during screen capture
2. gettimetick and timegettime
3. timeBeginPeriod and timeEndPeriod
4. QueryPerformanceTimer and QueryPerformanceCounter

To help simiplfy the process, i snipped a lot of code of the original project to only feature the screen capturing. Here is the complete routine (along with some remarked-out experimental code) for this:

(thanks in advanced for any help)

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, mmsystem,
  ExtCtrls, clipbrd, DXClass;

type
  TForm1 = class(TForm)
    Timer1: TTimer;
    Panel1: TPanel;
    m1: TMemo;
    btnCapOnOff: TButton;
    txtHandle: TEdit;
    Edit2: TEdit;
    stDataRate: TStaticText;
    btnCopy: TButton;
    btnSetHDC: TButton;
    dxt1: TDXTimer;
    sb1: TScrollBox;
    Splitter1: TSplitter;
    im1: TImage;
    procedure btnCapOnOffClick(Sender: TObject);
    procedure FormActivate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure capturewindow;
    procedure Timer1Timer(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure btnCopyClick(Sender: TObject);
    procedure btnSetHDCClick(Sender: TObject);
    procedure dxt1Timer(Sender: TObject; LagCount: Integer);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  start,
  finish : cardinal; //int64;
  i : integer;
  s : string;
  bm: tbitmap;
  dc: hdc=0;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  form1.DoubleBuffered:=true;
  sb1.DoubleBuffered:=true; // this is a scrollbox control
end;

procedure TForm1.FormActivate(Sender: TObject);
begin
  im1.Picture.Bitmap.PixelFormat:=pf24bit;
  im1.Width:=352;
  im1.Height:=240;
end;

procedure TForm1.btnSetHDCClick(Sender: TObject);
begin
  if dc=0 then dc := getdc(strToint(txtHandle.text));
end;

procedure TForm1.capturewindow;
begin
  //timeBeginPeriod(1);
  start := timegettime;
  //sleep(1);
  bitblt(bm.canvas.Handle, 0,0, 352,240, dc, 0,0, srccopy);
  finish := timegettime-start;
  //m1.lines.Add(intTostr(finish)); // debugging: to spill out timing values, etc.
  im1.Picture.Bitmap := bm;
  stDataRate.Caption := 'Date Rate: '+intTostr(finish) + ' fps or ms';
end;

procedure TForm1.dxt1Timer(Sender: TObject; LagCount: Integer);
begin
  capturewindow;
end;

procedure TForm1.Timer1Timer(Sender: TObject);
begin
//  capturewindow; // timer1 is too slow or unpredictable
end;

// button: a cheeters way to turn On or Off capturing
procedure TForm1.btnCapOnOffClick(Sender: TObject);
begin
  if btnCapOnOff.caption='Cap is Off' then begin
    btnCapOnOff.caption:='Cap is On';
    //timer1.Enabled:=true; // capture the window // too slow
    dxt1.Enabled:=true;   // capture the window // a better timer control component (delphiX)

  end else begin
    btnCapOnOff.Caption:='Cap is Off';
    //timer1.Enabled:=false; // too slow
    dxt1.Enabled:=false; // stop capturing the window // a better timer control component (delphiX)
  end;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  bm.free;
  releaseDC(dc,dc);
  //timeEndPeriod(1);
end;

procedure TForm1.btnCopyClick(Sender: TObject);
begin
  clipboard.assign(im1.picture.bitmap); // to take quick pics
end;

initialization
  bm := tbitmap.Create;
  bm.PixelFormat:=pf24bit;
  bm.Width:=352;
  bm.Height:=240;  beep;
end.

Answer 1

Actually hooking the software that's playing the video, and synchronizing to it, I'm not sure how to do that. But working on timing might help out. Assuming that the software playing the video is also well timed, you should be able to get a smooth capture.

This tutorial is useful: http://www.codeproject.com/Articles/1236/Timers-Tutorial

The "Multimedia Timers" offer good resolution (down to 1ms on most machines), and I've found them to be reliable.

What I would try is using the Performance Timer (queryperformancetimer, as you've already mentioned) to time your "CaptureWindow" procedure. Then, when you call "timesetevent" in a multimedia timer, subtract the amount of time the capture took from the overall time of a single frame, and use that as your "uDelay" value.

HowLongTimerShouldWait := LengthOfASingleFrame - TimeSpentCapturingPreviousFrame

The nice thing about the Multimedia Timers is that they let you use it as a 'one shot', where each interval can have a different delay period. I've generally set the timer to call a single procedure recursively, until it's flagged to stop.

This way, with a bit of fine tuning, you should be able to get capture rates are are within a +/-1ms tolerance of the actual video FPS.

Answer 2

As promised, here is the code i came up with based on some google searches and working them out in delphi. the following links did help me out some though (but due to c/c++/c# i could not translate as easily to delphi) so most of the final answer were based on lots of trial and error:

1. http://www.andrewduncan.ws/Timecodes/Timecodes.html
2. http://puredata.hurleur.com/sujet-990-framenumber-timecode-conversion

To my knowledge the routine works flawless. but just so you know, i like my numbers formated for spacing purposes, so i padded to 2-digits, this way there is not shriking back and forth as numbers progress past 59.

Heres how it works:

1. It computes the timecode based on the frame rate of your video source (ie 29.970 interlace or progressive, and 23.976 for 24p film) .. so just feed it a frame number and the function will return the timecode in string format.

Example Preporation/Useage:

1. put two Tedit's and one Tbutton control on your form1
2. in button1 onClick event, enter this: edit2.text := frameNo2timecode(strToint(edit1.text), 29.970);
3. now, run the program and enter your frame number in the first edit1.text
4. then, press the button1 control, it will compute the timecode in edit2.text

source code to calculate timecode:

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, math;

type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Edit2: TEdit;
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

function FrameNo2Timecode(fn: longint; rate: real): string;
var
  hours,mins,secs,milli: extended;
  hoursStr, minsStr, secsStr, milliStr: string;
function padzero(N: longint; Len: Integer): string;
begin
  FmtStr(Result, '%d', [N]);
  while Length(Result) < Len do
    Result := '0' + Result;
end;
begin
    hours := floor( (fn/rate)/3600) mod 60;
    hoursStr := padzero(floor(hours),2);
    mins  := floor( (fn/rate)/60.0) mod 60;
    minsstr  := padzero(floor(mins),2);
    secs  := floor( (fn/rate)) mod 60;
    secsstr  := padzero(floor(secs),2);
    milli := floor( (1000*fn/rate)) mod 6000 mod 1000;
    millistr := padzero(floor(milli),3);
    result := hoursStr +':'+ minsStr  +':'+ secsStr  +'.'+ milliStr;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  edit2.text := frameNo2timecode(strToint(edit1.text), 29.970);
end;

end.