用多媒体库 Bass.dll 播放 mp3 [10] - 使用回调函数

本例效果图:

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代码文件:

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unit Unit1;



interface



uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, StdCtrls, ExtCtrls, ComCtrls;



type

  TForm1 = class(TForm)

    OpenDialog1: TOpenDialog;

    TrackBar1: TTrackBar;

    Timer1: TTimer;

    Button1: TButton;

    Button2: TButton;

    Button3: TButton;

    procedure FormCreate(Sender: TObject);

    procedure Button1Click(Sender: TObject);

    procedure Button2Click(Sender: TObject);

    procedure Button3Click(Sender: TObject);

    procedure FormDestroy(Sender: TObject);

    procedure Timer1Timer(Sender: TObject);

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



uses Bass;



var

  hs: HSTREAM;  {流句柄}



{回调函数: MySync1; 尽管没有用到其中的任何参数, 但也要按指定的参数格式来写}

procedure MySync1(handle: HSYNC; channel, data, user: DWORD); stdcall;

begin

  Form1.Text := '开始播放了';

end;



{回调函数: MySync2}

{参数1: 是回调句柄, 它可有 BASS_ChannelSetSync 返回, 并可用 BASS_ChannelRemoveSync 删除}

{参数2: 流句柄}

{参数3: 不知道}

{参数4: 是 BASS_ChannelSetSync 指定的用户数据}

procedure MySync2(handle: HSYNC; channel, data, user: DWORD); stdcall;

begin

  Form1.Text := '已过中点';

  {假如播放到此(中间点)就从头反复, 可以这样:}

  //BASS_ChannelPlay(channel, True);

end;



{回调函数: MySync3; 尽管没有用到其中的任何参数, 但也必须按要求指定}

procedure MySync3(handle: HSYNC; channel, data, user: DWORD); stdcall;

begin

  Form1.Text := '播放完毕';

end;



{初始化}

procedure TForm1.FormCreate(Sender: TObject);

begin

  TrackBar1.Height := 23;

  Timer1.Enabled := False;

  Timer1.Interval := 100;



  if HiWord(BASS_GetVersion) <> BASSVERSION then

    MessageBox(0, '"Bass.dll" 文件版本不合适! ', nil, MB_ICONERROR);



  if not BASS_Init(-1, 44100, 0, 0, nil) then ShowMessage('初始化错误');

end;



{打开}

procedure TForm1.Button1Click(Sender: TObject);

var

  Mp3Path: AnsiString;

  Mp3Len: Cardinal;

begin

  BASS_StreamFree(hs);

  Timer1.Enabled := False;



  OpenDialog1.Filter := 'Mp3 文件(*.mp3)|*.mp3|Wav 文件(*.wav)|*wav';

  if OpenDialog1.Execute then

    Mp3Path := AnsiString(OpenDialog1.FileName);



  hs := BASS_StreamCreateFile(False, PAnsiChar(Mp3Path), 0, 0, 0);

  if hs < BASS_ERROR_ENDED then

    Text := '打开失败'

  else begin

    Text := string(Mp3Path);



    {先获取流的字节总长度, 下面有用}

    Mp3Len := BASS_ChannelGetLength(hs, BASS_POS_BYTE);

    TrackBar1.Max := Mp3Len;



    {开始播放是回调 MySync1}

    {参数1: 流句柄; 参数2: 参数类型; 参数3: 参数值; 参数4: 要回调函数指针; 参数5: 用户数据}

    BASS_ChannelSetSync(hs, BASS_SYNC_POS, 0, @MySync1, nil);



    {播放到中间时回调 MySync2}

    BASS_ChannelSetSync(hs, BASS_SYNC_POS, Mp3Len div 2, @MySync2, nil);



    {播放结束时回调 MySync3}

    BASS_ChannelSetSync(hs, BASS_SYNC_END, 0, @MySync3, nil);

    {当然也可以写做:}

    //BASS_ChannelSetSync(hs, BASS_SYNC_POS, Mp3Len, @MySync3, nil);

    {如果第二个参数同时指定 BASS_SYNC_ONETIME, 回调函数将只执行一次}

    BASS_ChannelSetSync(hs, BASS_SYNC_END or BASS_SYNC_ONETIME, 0, @MySync3, nil);

  end;

end;



{播放}

procedure TForm1.Button2Click(Sender: TObject);

begin

  BASS_ChannelPlay(hs, False);

  Timer1.Enabled := True;

end;



{暂停}

procedure TForm1.Button3Click(Sender: TObject);

begin

  BASS_ChannelPause(hs);

  Timer1.Enabled := False;

end;



procedure TForm1.FormDestroy(Sender: TObject);

begin

  BASS_Free;

end;



procedure TForm1.Timer1Timer(Sender: TObject);

begin

  if BASS_ChannelIsActive(hs) = BASS_ACTIVE_PLAYING then

    TrackBar1.Position := BASS_ChannelGetPosition(hs, BASS_POS_BYTE);

end;



end.


 
   

窗体文件:

---

object Form1: TForm1

  Left = 222

  Top = 114

  Caption = 'Form1'

  ClientHeight = 84

  ClientWidth = 254

  Color = clBtnFace

  Font.Charset = DEFAULT_CHARSET

  Font.Color = clWindowText

  Font.Height = -11

  Font.Name = 'Tahoma'

  Font.Style = []

  OldCreateOrder = False

  Position = poDesigned

  OnCreate = FormCreate

  OnDestroy = FormDestroy

  PixelsPerInch = 96

  TextHeight = 13

  object Button1: TButton

    Left = 8

    Top = 18

    Width = 75

    Height = 25

    Caption = #25171#24320

    TabOrder = 0

    OnClick = Button1Click

  end

  object Button2: TButton

    Left = 89

    Top = 18

    Width = 75

    Height = 25

    Caption = #25773#25918

    TabOrder = 1

    OnClick = Button2Click

  end

  object Button3: TButton

    Left = 170

    Top = 18

    Width = 75

    Height = 25

    Caption = #26242#20572

    TabOrder = 2

    OnClick = Button3Click

  end

  object TrackBar1: TTrackBar

    Left = 1

    Top = 53

    Width = 250

    Height = 28

    TabOrder = 3

  end

  object OpenDialog1: TOpenDialog

    Left = 72

    Top = 32

  end

  object Timer1: TTimer

    OnTimer = Timer1Timer

    Left = 152

    Top = 32

  end

end