macOS Audio Player
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Revision as of 10:11, 28 December 2019 by Trev (talk | contribs) (→See also: Added Multimedia Programming link)
This article applies to macOS only.
See also: Multiplatform Programming Guide
Overview
The Apple AVFoundation framework combines four major technology areas that together encompass a wide range of tasks for capturing, processing, synthesising, controlling, importing and exporting audiovisual media on Apple platforms. It is available from macOS 10.7 (Lion). The framework provides essential services for working with time-based audiovisual media.
- To play sound files, you can use AVAudioPlayer.
- To record audio, you can use AVAudioRecorder.
AVAudioPlayer
The AVAudioPlayer class lets you play sound in any audio format available in macOS from a file or memory. The properties of this class are used for managing information about a sound such as the playback point within the sound’s timeline and for accessing playback options such as volume and looping.
The supported audio formats are:
- AAC (MPEG-4 Advanced Audio Coding);
- ALAC (Apple Lossless);
- AMR (Adaptive Multi-rate);
- HE-AAC (MPEG-4 High Efficiency AAC);
- iLBC (internet Low Bit Rate Codec);
- Linear PCM (uncompressed, linear pulse code modulation);
- MP3 (MPEG-1 audio layer 3); and
- µ-law and a-law.
Using an audio player you can:
- Play sounds of any duration (unlike System Sound Services that has a 30 second limit);
- Play sounds from files or memory buffers;
- Play sounds when your application is in the background;
- Loop sounds (including indefinitely);
- Play multiple sounds simultaneously, one sound per audio player, with precise synchronisation;
- Control relative playback level, stereo positioning, and playback rate for each sound you are playing;
- Seek to a particular point in a sound file, which supports such application features as fast forward and rewind; and
- Obtain data you can use for playback-level metering.
Example Code
Note: Not every method in the AVAudioPlayer class has been implemented in the code below. Those methods needed for play audio from a file, pause playback, resume playback, stop playback, set volume and set looping, plus a few others, have been implemented. Check the Apple documentation for the rest. The implemented methods are described in detail in the code below.//
// Note: Free Pascal v3.3.1 (trunk), revision r42640, was used 27-Dec-2019
//
unit unit1;
{$mode objfpc}{$H+}
{$modeswitch objectivec1}
{$linkframework AVFoundation}
interface
uses
...
MacOSAll,
CocoaAll,
LCLType,
...
type
{ TForm1 }
AVAudioPlayer = objcclass external(NSObject)
public
{Plays a sound asynchronously. Calling this method implicitly calls the
prepareToPlay() method if the audio player is not already prepared to play.}
function play: Boolean; message 'play';
{A value of 0.0 indicates silence; a value of 1.0 (the default) indicates
full volume for the audio player instance. Use this property to control an
audio player’s volume relative to other audio output.}
function volume: Single; message 'volume';
procedure setVolume(newValue: Single); message 'setVolume:';
{A value of 0, which is the default, means to play the sound once.
Set a positive integer value to specify the number of times to return
to the start and play again. For example, specifying a value of 1
results in a total of two plays of the sound. Set any negative
integer value to loop the sound indefinitely until you call the
stop() method.}
function numbreOfLoops: Integer; message 'numberOfLoops';
procedure setNumberOfLoops(newValue: Integer); message 'setNumberOfLoops:';
{A Boolean value that indicates whether the audio player is playing (true)
or not (false).}
function isPlaying: Boolean; message 'isPlaying';
{Calling this method preloads buffers and acquires the audio hardware
needed for playback, which minimises the lag between calling the play()
method and the start of sound output.}
function prepareToPlay: Boolean; message 'prepareToPlay';
{Pauses playback; sound remains ready to resume playback from where
it left off. It does not release the audio hardware that was acquired
on calling play() or prepareToPlay().}
procedure pause; message 'pause';
{The stop method does not reset the value of the currentTime property to 0.
If you call stop during playback and then call play(), playback resumes
at the point where it left off. Callikng this method undoes the setup
performed on calling the play() or prepareToPlay() methods.}
procedure stop; message 'stop';
{The total duration, in seconds, of the sound associated with the audio
player.}
function duration: Double; message 'duration';
end;
TForm1 = class(TForm)
...
private
public
end;
var
Form1: TForm1;
MyAudioPlayer : AVAudioPlayer = Nil;
implementation
...
// Convert NSStrings function
function NSStringToString(ns: NSString): String;
var
pathStr: shortstring;
begin
CFStringGetPascalString(CFStringRef(ns),@pathStr,255,CFStringGetSystemEncoding());
Result := pathStr;
end;
// Play audio procedure
procedure PlayAudio(audioFileName : NSString; numberOfLoops: Integer);
var
path: NSString;
url : NSURL;
err : NSError;
begin
// Path to your application bundle's resource directory
// with the mp3 filename appended
path := NSBundle.mainBundle.resourcePath.stringByAppendingPathComponent(audioFileName);
url := NSURL.fileURLWithPath(path);
MyAudioPlayer := AVAudioPlayer.alloc.initWithContentsOfURL_error(url, @err);
if Assigned(MyAudioPlayer) then
begin
MyAudioPlayer.setNumberOfLoops(numberOfLoops);
MyAudioPlayer.play
end
else
// Use the Applications > Utilities > Console application to find error messages
NSLog(NSStr('Error in procedure PlaySound(): %@'), err);
end;
...
// Play audio file located in your application bundle Resources directory
// This particular demo file can be found on your Mac at:
// /Applications/iPhoto.app/Contents/Resources/Music/Minuet in G.mp3
// and should be copied to your application bundle Resources directory.
procedure TForm1.MenuItem23Click(Sender: TObject);
begin
PlayAudio(NSStr('Minuet in G.mp3'), 0);
end;
// Pause audio
procedure TForm1.MenuItem24Click(Sender: TObject);
begin
MyAudioPlayer.pause;
end;
// Resume audio
procedure TForm1.MenuItem25Click(Sender: TObject);
begin
// Note: This will restart the audio where it left off after a pause or stop
// Do not create yet another audio player by calling PlayAudio() again :-)
MyAudioPlayer.play;
end;
// Stop audio
procedure TForm1.MenuItem26Click(Sender: TObject);
begin
MyAudioPlayer.stop;
end;
...
finalization
If (Assigned (MyAudioPlayer)) then
begin
MyAudioPlayer.Release;
MyAudioPlayer := Nil;
end;
end.
