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comparison src/cdrom/macosx/SDL_syscdrom_c.h @ 613:9c6717a1c66f

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Added MacOS X CD-ROM audio support (thanks Max and Darrell)
author Sam Lantinga <slouken@libsdl.org>
date Tue, 15 Apr 2003 16:33:56 +0000
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612:0648505b1f8b 613:9c6717a1c66f
1 /*
2 SDL - Simple DirectMedia Layer
3 Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002 Sam Lantinga
4
5 This library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Library General Public
7 License as published by the Free Software Foundation; either
8 version 2 of the License, or (at your option) any later version.
9
10 This library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Library General Public License for more details.
14
15 You should have received a copy of the GNU Library General Public
16 License along with this library; if not, write to the Free
17 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18
19 Sam Lantinga
20 slouken@libsdl.org
21 */
22
23
24 /***********************************************************************************
25 Implementation Notes
26 *********************
27
28 This code has several limitations currently (all of which are proabaly fixable):
29
30 1. A CD-ROM device is inferred from a mounted cdfs volume, so device 0 is
31 not necessarily the first CD-ROM device on the system. (Somewhat easy to fix
32 by useing the device name from the volume id's to reorder the volumes)
33
34 2. You can only open and control 1 CD-ROM device at a time. (Challenging to fix,
35 due to extensive code restructuring)
36
37 3. The status reported by SDL_CDStatus only changes to from CD_PLAYING to CD_STOPPED in
38 1-second intervals (because the audio is buffered in 1-second chunks) If
39 the audio data is less than 1 second, the remainder is filled with silence.
40
41 If you need to play sequences back-to-back that are less that 1 second long,
42 use the frame position to determine when to play the next sequence, instead
43 of SDL_CDStatus.
44
45 This may be possible to fix with a clever usage of the AudioUnit API.
46
47 4. When new volumes are inserted, our volume information is not updated. The only way
48 to refresh this information is to reinit the CD-ROM subsystem of SDL. To fix this,
49 one would probably have to fix point 1 above first, then figure out how to register
50 for a notification when new media is mounted in order to perform an automatic
51 rescan for cdfs volumes.
52
53
54
55 So, here comes a description of how this all works.
56
57 < Initializing >
58
59 To get things rolling, we have to locate mounted volumes that contain
60 audio (since nearly all Macs don't have analog audio-in on the sound card).
61 That's easy, since these volumes have a flag that indicates this special
62 filesystem. See DetectAudioCDVolumes() in CDPlayer.cpp for this code.
63
64 Next, we parse the invisible .TOC.plist in the root of the volume, which gets us
65 the track information (number, offset, length, leadout, etc). See ReadTOCData() in
66 CDPlayer.cpp for the skinny on this.
67
68
69 < The Playback Loop >
70
71 Now come the tricky parts. Let's start with basic audio playback. When a frame
72 range to play is requested, we must first find the .aiff files on the volume,
73 hopefully in the right order. Since these files all begin with a number "1 Audio Track",
74 etc, this is used to determine the correct track order.
75
76 Once all files are determined, we have to find what file corresponds to the start
77 and length parameter to SDL_SYS_CDPlay(). Again, this is quite simple by walking the
78 cdrom's track list. At this point, we also save the offset to the next track and frames
79 remaining, if we're going to have to play another file after the first one. See
80 GetFileForOffset() for this code.
81
82 At this point we have all info needed to start playback, so we hand off to the LoadFile()
83 function, which proceeds to do its magic and plays back the file.
84
85 When the file is finished playing, CompletionProc() is invoked, at which time we can
86 play the next file if the previously saved next track and frames remaining
87 indicates that we should.
88
89
90 < Magic >
91
92 OK, so it's not really magic, but since I don't fully understand all the hidden details it
93 seems like it to me ;-) The API's involved are the AudioUnit and AudioFile API's. These
94 appear to be an extension of CoreAudio for creating modular playback and f/x entities.
95 The important thing is that CPU usage is very low and reliability is very high. You'd
96 be hard-pressed to find a way to stutter the playback with other CPU-intensive tasks.
97
98 One part of this magic is that it uses multiple threads, which carries the usual potential
99 for disaster if not handled carefully. Playback currently requires 4 additional threads:
100 1. The coreaudio runloop thread
101 2. The coreaudio device i/o thread
102 3. The file streaming thread
103 4. The notification/callback thread
104
105 The first 2 threads are necessary evil - CoreAudio creates this no matter what the situation
106 is (even the SDL sound implementation creates theses suckers). The last two are are created
107 by us.
108
109 The file is streamed from disk using a threaded double-buffer approach.
110 This way, the high latency operation of reading from disk can be performed without interrupting
111 the real-time device thread (which amounts to avoiding dropouts). The device thread grabs the
112 buffer that isn't being read and sends it to the CoreAudio mixer where it eventually gets
113 to the sound card.
114
115 The device thread posts a notification when the file streaming thread is out of data. This
116 notification must be handled in a separate thread to avoid potential deadlock in the
117 device thread. That's where the notification thread comes in. This thread is signaled
118 whenever a notification needs to be processed, so another file can be played back if need be.
119
120 The API in CDPlayer.cpp contains synchronization because otherwise both the notification thread
121 and main thread (or another other thread using the SDL CD api) can potentially call it at the same time.
122
123 ************************************************************************************/
124
125
126 #include "SDL_cdrom.h"
127 #include "SDL_syscdrom.h"
128
129 #include "CDPlayer.h"
130
131 #define kErrorFakeDevice "Error: Cannot proceed since we're faking a CD-ROM device. Reinit the CD-ROM subsystem to scan for new volumes."
132