[Solved] How to write an AVAudioEngine TapOnBus callback?

[freq]

Hi,

have an issue with a simple task to attach a tapBlock with the following function from an audio node (comment out the call and below sample code works fine)

inputNode.installTapOnBus_bufferSize_format_block(0,1024,nil,@tapBlock)

I don't know how to write a propper tapBlock callback function so that the following audio engine sequence doesn't crashes (I assume the tapBlock callback function is wrong defined or needs a Objective-C wrapper? Can't find any sample codes even for other OBjective-C callback cases). Any hint very welcome!

Thanks in advance!

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode delphi}
4. {$modeswitch objectivec1}
5. {$modeswitch cvar}
6. {$packrecords c}
7.  
8.  
9. {$linkframework AVFoundation}
10.  
11. interface
12.  
13. uses
14.   Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs,
15.   StdCtrls,
16.  
17.   AVFoundation,
18.   CoreAudio, MacTypes, SecBase,DefinedClassesFoundation;
19.  
20. type
21.  
22.   { TForm1 }
23.  
24.   TForm1 = class(TForm)
25.     Button1: TButton;
26.     Label1: TLabel;
27.     procedure Button1Click(Sender: TObject);
28.   private
29.  
30.     audioEngine: AVAudioEngine;
31.     unitReverb:AVAudioUnitReverb;
32.     inputNode:AVAudioInputNode;
33.  
34.     procedure SetupAudioEngine;
35.  
36.   public
37.  
38.   end;
39.  
40. var
41.   Form1: TForm1;
42.  
43. implementation
44.  
45. {$R *.lfm}
46.  
47.  
48. // issue probably in that definition, it is even never called
49.  
50. procedure tapBlock(buffer: AVAudioPCMBufferPtr; when:AVAudioTimePtr);
51. var i:integer;
52. begin
53. i:=0;
54. end;
55.  
56. { TForm1 }
57.  
58. procedure TForm1.Button1Click(Sender: TObject);
59. begin
60.       SetupAudioEngine;
61. end;
62.  
63. procedure TForm1.SetupAudioEngine;
64. var inputFormat: AVAudioFormat;
65.     outError:NSError;
66.  
67. begin
68.  
69.  audioEngine:=  AVAudioEngine.alloc.init;
70.  unitReverb:= AVAudioUnitReverb.alloc.init;
71.  
72.  audioEngine.attachNode(unitReverb);
73.  
74.  inputNode:= audioEngine.inputNode;
75.  inputFormat:=  unitReverb.inputFormatForBus(0);
76.  
77.  inputNode.installTapOnBus_bufferSize_format_block(0,1024,nil,@tapBlock);       // this creates the crash!
78.  
79.  audioEngine.connect_to_format(inputNode,unitReverb, inputFormat);
80.  audioEngine.connect_to_format(unitReverb,audioEngine.outputNode, inputFormat);
81.  
82. if audioEngine.startAndReturnError(@outError) then
83.    begin
84.    Label1.Caption:='ok';
85.    end;
86. end;
87.  
88. end.
89.  

[Zvoni]

Are you sure it's the Callback?
I'd rather look at the 3rd Parameter "Format" --> You pass nil

https://developer.apple.com/documentation/avfaudio/avaudionode/1387122-installtaponbus?language=objc

[freq]

Are you sure it's the Callback?
I'd rather look at the 3rd Parameter "Format" --> You pass nil

https://developer.apple.com/documentation/avfaudio/avaudionode/1387122-installtaponbus?language=objc

Yes, checked, same crash with:

Code: Pascal  [Select][+][-]

1. inputFormat:=  unitReverb.inputFormatForBus(0);
2.  
3.  tab:= @tapBlock;
4.  unitReverb.installTapOnBus_bufferSize_format_block(0,1024,inputFormat,tab);       // this creates the crash!  

Assume that there must be something special in the way Objective-C handles a callback, is that "block" really a callback function or more an NSOBject something? 

[Zvoni]

No idea, since it's not my corner of expertise.

But your Procedure declaration looks good, IMO. Both arguments appear to be Pointers, and it expects a procedure (not a function)

The only thing i'm not sure about is "visibility" of your callback-procedure and/or calling-convention

@visibility: You have no "Forward"-Declaration under "Interface" --> But not sure about that.
@Calling-convention --> What's the standard calling-convention in Apple's objective C? cdecl?

[freq]

@visibility: You have no "Forward"-Declaration under "Interface" --> But not sure about that.
@Calling-convention --> What's the standard calling-convention in Apple's objective C? cdecl?

Intresting ideas! Thanks, but unfortunately no success with both, I tried to add callback to interface and also tried with removed cdecl (though cdecl is the standard for objective C afaik). I'm still pretty sure that its a callback definition issue as it only crashes when activating the audio engine and when executed the installTapOnBus_bufferSize_format_block before.

Interesting that the block definition contains a ^ operator ... how to translate that?

typedef void (^AVAudioNodeTapBlock)(AVAudioPCMBuffer *buffer, AVAudioTime *when);

[Zvoni]

Intresting ideas! Thanks, but unfortunately no success with both, I tried to add callback to interface and also tried with removed cdecl (though cdecl is the standard for objective C afaik). I'm still pretty sure that its a callback definition issue as it only crashes when activating the audio engine and when executed the installTapOnBus_bufferSize_format_block before.

You might be onto something here, because the standard calling convention in FPC is "Register", not cdecl.
I'd really research this.

Interesting that the block definition contains a ^ operator ... how to translate that?

typedef void (^AVAudioNodeTapBlock)(AVAudioPCMBuffer *buffer, AVAudioTime *when);

Usually this indicates a Function-Pointer, and you provide (correctly!) the "@"-Symbol in your call to it, but you're in mode Delphi!
IIRC, in mode delphi you shouldn't provide/need the "@"-Symbol, but i'm not sure about it, since i've never used mode delphi
try

Code: Pascal  [Select][+][-]

1. unitReverb.installTapOnBus_bufferSize_format_block(0,1024,inputFormat,tapBlock); //No @-Symbol!

EDIT: Maybe a BINGO?
https://www.freepascal.org/docs-html/prog/progse74.html

D.3 Delphi mode

This mode is selected by the $MODE DELPHI switch. It tries to emulate, as closely as possible, the behavior of Delphi 4 till recent versions of Delphi . On the command line, this mode is selected by the -Mdelphi switch.

1. You cannot use the address operator to assign procedural variables.

"@"-Symbol is the Address-Operator

[freq]

You might be onto something here, because the standard calling convention in FPC is "Register", not cdecl.
I'd really research this.

No, unfortunately no success with "Register"

Usually this indicates a Function-Pointer, and you provide (correctly!) the "@"-Symbol in your call to it, but you're in mode Delphi!

No, unfortunately also no luck to switch to {$mode objfpc}{$H+}  mode

 

[Zvoni]

No, unfortunately no success with "Register"

I think you misunderstood: if you don’t declare the calling convention, FreePascal uses „register“ by default.
Research if calling convention in Objective C is cdecl or something else

[freq]

I think you misunderstood: if you don’t declare the calling convention, FreePascal uses „register“ by default.
Research if calling convention in Objective C is cdecl or something else

Thanks for the clarification, but unfortunately with our without cdecl it doesn't work. 

[freq]

Thanks for all but I found the solution with the input from here that deals with a similar callback topic:
https://forum.lazarus.freepascal.org/index.php?topic=42001.45

As suspected it was a declaration topic and we have to use cblock:

This code works now without crashing  :

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4. {$modeswitch objectivec1}
5. {$packrecords c}
6. {$modeswitch cblocks}
7.  
8. {$linkframework AVFoundation}
9.  
10. interface
11.  
12. uses
13.   Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs,
14.   StdCtrls,
15.  
16.   AVFoundation,
17.   CoreAudio, MacTypes, SecBase,DefinedClassesFoundation;
18.  
19. type
20.  
21.   { TForm1 }
22.  
23.   TForm1 = class(TForm)
24.     Button1: TButton;
25.     Label1: TLabel;
26.     procedure Button1Click(Sender: TObject);
27.   private
28.  
29.     inputNode: AVAudioInputNode;
30.     audioEngine: AVAudioEngine;
31.     format: AVAudioFormat;
32.  
33.     mixerNode:AVAudioMixerNode;
34.  
35.     procedure SetupAudioEngine;
36.  
37.   public
38.  
39.     procedure tapBlock(buffer: AVAudioPCMBufferPtr; when:AVAudioTimePtr);
40.  
41.   end;
42.  
43.  
44. var
45.   Form1: TForm1;
46.  
47. implementation
48.  
49. {$R *.lfm}
50.  
51.  
52. type
53.   tblock = reference to procedure(buffer: AVAudioPCMBufferPtr; when:AVAudioTimePtr); cdecl; cblock;
54.  
55.  
56. procedure TForm1.tapBlock(buffer: AVAudioPCMBufferPtr; when:AVAudioTimePtr);
57. var i:integer;
58. begin
59. i:=0;
60. end;
61.  
62. procedure TForm1.Button1Click(Sender: TObject);
63. begin
64.       SetupAudioEngine;
65. end;
66.  
67. procedure TForm1.SetupAudioEngine;
68. var
69.     outError:NSError;
70.     s:double;
71.     tab: tblock;
72.  
73. begin
74.  
75.  tab:= @tapBlock;
76.  
77.  audioEngine:=  AVAudioEngine.alloc.init;
78.  
79.  inputNode:=audioEngine.inputNode;
80.  
81.  mixerNode:= AVAudioMixerNode.alloc.init;
82.  audioEngine.attachNode(mixerNode);
83.  format := inputNode.inputFormatForBus(0);
84.  
85.   mixerNode.installTapOnBus_bufferSize_format_block(0,2048,mixerNode.outputFormatForBus(0), OpaqueCBlock(tab)); // add tap
86.  
87.  audioEngine.connect_to_format(inputNode,mixerNode,format);
88.  audioEngine.connect_to_format(mixerNode, audioEngine.outputNode, format);
89.  
90.  audioEngine.prepare;
91.  
92. if audioEngine.startAndReturnError(@outError) then
93.    begin
94.  
95.    Label1.Caption:='ok';
96.    end;
97. end;
98.  
99. end.
100.  
101.