用多媒体库 Bass.dll 播放 mp3 [5] - 设置与获取音量、相位

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;
    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;
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 := '打开失败'
  else begin
    TrackBar1Change(nil);
    TrackBar2Change(nil);
    Text := string(Mp3Path);
  end;
end;

{播放}
procedure TForm1.Button2Click(Sender: TObject);
begin
  BASS_ChannelPlay(hs, False);
end;

{暂停}
procedure TForm1.Button3Click(Sender: TObject);
begin
  BASS_ChannelPause(hs);
end;

{设置和获取音量}
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('当前音量值: %f', [vol]);
end;

{设置和获取相位}
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('当前相位值: %f', [pan]);
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  BASS_Free;
end;

end.

窗体文件:

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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
end