用多媒體庫 Bass.dll 播放 mp3 [5] - 設置與獲取音量、相位

本例效果圖:

　　代碼文件:unit Unit1;
interface
uses
　Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
　Dialogs, StdCtrls, ExtCtrls, ComCtrls;
type
　TForm1 = class(TForm)
　　OpenDialog1: TOpenDialog;
　　Button1: TButton;
　　Button2: TButton;
　　Button3: TButton;
　　TrackBar1: TTrackBar;
　　TrackBar2: TTrackBar;
　　Label1: TLabel;
　　Label2: TLabel;
　　procedure FormCreate(Sender: TObject);
　　procedure Button1Click(Sender: TObject);
　　procedure Button2Click(Sender: TObject);
　　procedure Button3Click(Sender: TObject);
　　procedure TrackBar1Change(Sender: TObject);
　　procedure TrackBar2Change(Sender: TObject);
　　procedure FormDestroy(Sender: TObject);
　end;
var
　Form1: TForm1;
implementation
{$R *.dfm}
uses Bass;
var
　hs: HSTREAM;　{流句柄}
procedure TForm1.FormCreate(Sender: TObject);
begin
　TrackBar1.ShowSelRange := False;
　TrackBar1.Min := 0;
　TrackBar1.Max := 40;
　TrackBar1.Position := TrackBar1.Max;
　TrackBar2.ShowSelRange := False;
　TrackBar2.Min := -20;
　TrackBar2.Max := 20;
　TrackBar2.Position := 0;
　if HiWord(BASS_GetVersion) <> BASSVERSION then
　　MessageBox(0, '"Bass.dll" 文件版本不合適! ', nil, MB_ICONERROR);
　if not BASS_Init(-1, 44100, 0, 0, nil) then
　　ShowMessage('初始化錯誤');
end;
{打開}
procedure TForm1.Button1Click(Sender: TObject);
var
　Mp3Path: AnsiString;
begin
　BASS_StreamFree(hs);
　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 := '打開失敗'
　else begin
　　TrackBar1Change(nil);
　　TrackBar2Change(nil);
　　Text := string(Mp3Path);
　end;
end;
{播放}
procedure TForm1.Button2Click(Sender: TObject);
begin
　BASS_ChannelPlay(hs, False);
end;
{暫停}
procedure TForm1.Button3Click(Sender: TObject);
begin
　BASS_ChannelPause(hs);
end;
{設置和獲取音量}
procedure TForm1.TrackBar1Change(Sender: TObject);
var
　vol: Single;
begin
　BASS_ChannelSetAttribute(hs, BASS_ATTRIB_VOL, TrackBar1.Position / TrackBar1.Max);
　BASS_ChannelGetAttribute(hs, BASS_ATTRIB_VOL, vol);
　Label1.Caption := Format('當前音量值: %f', [vol]);
end;
{設置和獲取相位}
procedure TForm1.TrackBar2Change(Sender: TObject);
var
　pan: Single;
begin
　BASS_ChannelSetAttribute(hs, BASS_ATTRIB_PAN, TrackBar2.Position / TrackBar2.Max);
　BASS_ChannelGetAttribute(hs, BASS_ATTRIB_PAN, pan);
　Label2.Caption := Format('當前相位值: %f', [pan]);
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
　BASS_Free;
end;
end.窗體文件:object Form1: TForm1
　Left = 205
　Top = 107
　Caption = 'Form1'
　ClIEntHeight = 157
　ClIEntWidth = 286
　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 Label1: TLabel
　　Left = 32
　　Top = 59
　　Width = 31
　　Height = 13
　　Caption = 'Label1'
　end
　object Label2: TLabel
　　Left = 32
　　Top = 109
　　Width = 31
　　Height = 13
　　Caption = 'Label2'
　end
　object Button1: TButton
　　Left = 24
　　Top = 17
　　Width = 75
　　Height = 25
　　Caption = #25171#24320
　　TabOrder = 0
　　OnClick = Button1Click
　end
　object Button2: TButton
　　Left = 105
　　Top = 17
　　Width = 75
　　Height = 25
　　Caption = #25773#25918
　　TabOrder = 1
　　OnClick = Button2Click
　end
　object Button3: TButton
　　Left = 186
　　Top = 17
　　Width = 75
　　Height = 25
　　Caption = #26242#20572
　　TabOrder = 2
　　OnClick = Button3Click
　end
　object TrackBar1: TTrackBar
　　Left = 24
　　Top = 74
　　Width = 237
　　Height = 32
　　TabOrder = 3
　　OnChange = TrackBar1Change
　end
　object TrackBar2: TTrackBar
　　Left = 24
　　Top = 123
　　Width = 237
　　Height = 28
　　TabOrder = 4
　　OnChange = TrackBar2Change
　end
　object OpenDialog1: TOpenDialog
　　Left = 248
　　Top = 32
　end