Implemented support for multiple decoders per file name extension, with a floating point priority control per interface. In the event that more than one input is registered to a given extension, and we match that extension, it will be passed off to an instance of the multi-decoder wrapper, which will try opening the file with all of the decoders in order of priority, until either one of them accepts it, or all of them have failed. This paves the way for adding a VGMSTREAM input, so I can give it a very low priority, since it has several formats that are verified by file name extension only. All current inputs have been given a priority of 1.0, except for CoreAudio, which was given a priority of 0.5, because it contains an MP3 and AC3 decoders that I'd rather not use if I don't have to.

Audio/CogAudio.xcodeproj/project.pbxproj

@@ -44,6 +44,8 @@
 		17F94DD60B8D0F7000A34E87 /* PluginController.m in Sources */ = {isa = PBXBuildFile; fileRef = 17F94DD40B8D0F7000A34E87 /* PluginController.m */; };
 		17F94DDD0B8D101100A34E87 /* Plugin.h in Headers */ = {isa = PBXBuildFile; fileRef = 17F94DDC0B8D101100A34E87 /* Plugin.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		8384912718080FF100E7332D /* Logging.h in Headers */ = {isa = PBXBuildFile; fileRef = 8384912618080FF100E7332D /* Logging.h */; };
+		839366671815923C006DD712 /* CogDecoderMulti.h in Headers */ = {isa = PBXBuildFile; fileRef = 839366651815923C006DD712 /* CogDecoderMulti.h */; };
+		839366681815923C006DD712 /* CogDecoderMulti.m in Sources */ = {isa = PBXBuildFile; fileRef = 839366661815923C006DD712 /* CogDecoderMulti.m */; };
 		8DC2EF570486A6940098B216 /* Cocoa.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 1058C7B1FEA5585E11CA2CBB /* Cocoa.framework */; };
 		8E8D3D2F0CBAEE6E00135C1B /* AudioContainer.h in Headers */ = {isa = PBXBuildFile; fileRef = 8E8D3D2D0CBAEE6E00135C1B /* AudioContainer.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		8E8D3D300CBAEE6E00135C1B /* AudioContainer.m in Sources */ = {isa = PBXBuildFile; fileRef = 8E8D3D2E0CBAEE6E00135C1B /* AudioContainer.m */; };
@@ -107,6 +109,8 @@
 		17F94DDC0B8D101100A34E87 /* Plugin.h */ = {isa = PBXFileReference; fileEncoding = 30; lastKnownFileType = sourcecode.c.h; path = Plugin.h; sourceTree = "<group>"; };
 		32DBCF5E0370ADEE00C91783 /* CogAudio_Prefix.pch */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = CogAudio_Prefix.pch; sourceTree = "<group>"; };
 		8384912618080FF100E7332D /* Logging.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = Logging.h; path = ../../Utils/Logging.h; sourceTree = "<group>"; };
+		839366651815923C006DD712 /* CogDecoderMulti.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = CogDecoderMulti.h; sourceTree = "<group>"; };
+		839366661815923C006DD712 /* CogDecoderMulti.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = CogDecoderMulti.m; sourceTree = "<group>"; };
 		8DC2EF5A0486A6940098B216 /* Info.plist */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.plist; path = Info.plist; sourceTree = "<group>"; };
 		8DC2EF5B0486A6940098B216 /* CogAudio.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; includeInIndex = 0; path = CogAudio.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		8E8D3D2D0CBAEE6E00135C1B /* AudioContainer.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = AudioContainer.h; sourceTree = "<group>"; };
@@ -189,6 +193,8 @@
 				17B6192F0B909BC300BC003F /* AudioPropertiesReader.m */,
 				17ADB13A0B97926D00257CA2 /* AudioSource.h */,
 				17ADB13B0B97926D00257CA2 /* AudioSource.m */,
+				839366651815923C006DD712 /* CogDecoderMulti.h */,
+				839366661815923C006DD712 /* CogDecoderMulti.m */,
 				17F94DD30B8D0F7000A34E87 /* PluginController.h */,
 				17F94DD40B8D0F7000A34E87 /* PluginController.m */,
 				17D21C750B8BE4BA00D1EBDE /* Chain */,
@@ -317,6 +323,7 @@
 				17A2D3C50B8D1D37000778C4 /* AudioDecoder.h in Headers */,
 				17C940230B900909008627D6 /* AudioMetadataReader.h in Headers */,
 				17B619300B909BC300BC003F /* AudioPropertiesReader.h in Headers */,
+				839366671815923C006DD712 /* CogDecoderMulti.h in Headers */,
 				17ADB13C0B97926D00257CA2 /* AudioSource.h in Headers */,
 				8EC1225F0B993BD500C5B3AD /* ConverterNode.h in Headers */,
 				8384912718080FF100E7332D /* Logging.h in Headers */,
@@ -397,6 +404,7 @@
 				17D21CE00B8BE5B400D1EBDE /* VirtualRingBuffer.m in Sources */,
 				17D21CF40B8BE5EF00D1EBDE /* Semaphore.m in Sources */,
 				17D21DC80B8BE79700D1EBDE /* CoreAudioUtils.m in Sources */,
+				839366681815923C006DD712 /* CogDecoderMulti.m in Sources */,
 				17D21EBE0B8BF44000D1EBDE /* AudioPlayer.m in Sources */,
 				17F94DD60B8D0F7000A34E87 /* PluginController.m in Sources */,
 				17A2D3C60B8D1D37000778C4 /* AudioDecoder.m in Sources */,

Audio/CogDecoderMulti.h

@@ -0,0 +1,20 @@
+//
+//  CogDecoderMulti.h
+//  CogAudio
+//
+//  Created by Christopher Snowhill on 10/21/13.
+//
+//
+
+#import <Cocoa/Cocoa.h>
+#import "Plugin.h"
+
+@interface CogDecoderMulti : NSObject <CogDecoder> {
+    NSArray *theDecoders;
+    id<CogDecoder> theDecoder;
+    NSMutableArray *cachedObservers;
+}
+
+-(id)initWithDecoders:(NSArray *)decoders;
+
+@end

Audio/CogDecoderMulti.m

@@ -0,0 +1,129 @@
+//
+//  CogDecoderMulti.m
+//  CogAudio
+//
+//  Created by Christopher Snowhill on 10/21/13.
+//
+//
+
+#import "CogDecoderMulti.h"
+
+@implementation CogDecoderMulti
+
++ (NSArray *)mimeTypes
+{
+    return nil;
+}
+
++ (NSArray *)fileTypes
+{
+    return nil;
+}
+
++ (float)priority
+{
+    return -1.0;
+}
+
+- (id)initWithDecoders:(NSArray *)decoders
+{
+    self = [super init];
+    if ( self )
+    {
+        NSMutableArray *sortedDecoders = [NSMutableArray arrayWithArray:decoders];
+        [sortedDecoders sortUsingComparator:
+         ^NSComparisonResult(id obj1, id obj2)
+         {
+             NSString *classString1 = (NSString *)obj1;
+             NSString *classString2 = (NSString *)obj2;
+             
+             Class decoder1 = NSClassFromString(classString1);
+             Class decoder2 = NSClassFromString(classString2);
+             
+             float priority1 = [decoder1 priority];
+             float priority2 = [decoder2 priority];
+             
+             if (priority1 == priority2) return NSOrderedSame;
+             else if (priority1 > priority2) return NSOrderedAscending;
+             else return NSOrderedDescending;
+         }];
+        theDecoders = sortedDecoders;
+        theDecoder = nil;
+        cachedObservers = [[[NSMutableArray alloc] init] autorelease];
+    }
+    return self;
+}
+
+- (NSDictionary *)properties
+{
+    if ( theDecoder != nil ) return [theDecoder properties];
+    return nil;
+}
+
+- (int)readAudio:(void *)buffer frames:(UInt32)frames
+{
+    if ( theDecoder != nil ) return [theDecoder readAudio:buffer frames:frames];
+    return 0;
+}
+
+- (BOOL)open:(id<CogSource>)source
+{
+    for (NSString *classString in theDecoders)
+    {
+        Class decoder = NSClassFromString(classString);
+        theDecoder = [[decoder alloc] init];
+        for (NSDictionary *obsItem in cachedObservers) {
+            [theDecoder addObserver:[obsItem objectForKey:@"observer"] forKeyPath:[obsItem objectForKey:@"keyPath"] options:[obsItem objectForKey:@"options"] context:[obsItem objectForKey:@"context"]];
+        }
+        if ([theDecoder open:source])
+            return YES;
+        for (NSDictionary *obsItem in cachedObservers) {
+            [theDecoder removeObserver:[obsItem objectForKey:@"observer"] forKeyPath:[obsItem objectForKey:@"keyPath"]];
+        }
+        [theDecoder release];
+        [source seek:0 whence:SEEK_SET];
+    }
+    theDecoder = nil;
+    return NO;
+}
+
+- (long)seek:(long)frame
+{
+    if ( theDecoder != nil ) return [theDecoder seek:frame];
+    return -1;
+}
+
+- (void)close
+{
+    if ( theDecoder != nil ) {
+        [theDecoder close];
+        [theDecoder release];
+        theDecoder = nil;
+    }
+}
+
+- (BOOL)setTrack:(NSURL *)track
+{
+    if ( theDecoder != nil && [theDecoder respondsToSelector: @selector(setTrack:)] ) return [theDecoder setTrack:track];
+    return NO;
+}
+
+/* By the current design, the core adds its observers to decoders before they are opened */
+- (void)addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(void *)context
+{
+    [cachedObservers addObject:[NSDictionary dictionaryWithObjectsAndKeys:observer, @"observer", keyPath, @"keyPath", options, @"options", context, @"context", nil]];
+}
+
+- (void)removeObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath
+{
+    if ( theDecoder != nil )
+        [theDecoder removeObserver:observer forKeyPath:keyPath];
+    for (NSDictionary *obsItem in cachedObservers)
+    {
+        if ([obsItem objectForKey:@"observer"] == observer && [keyPath isEqualToString:[obsItem objectForKey:@"keyPath"]]) {
+            [cachedObservers removeObject:obsItem];
+        }
+    }
+}
+
+@end

Audio/Plugin.h

@@ -25,6 +25,7 @@
 @required
 + (NSArray *)mimeTypes;
 + (NSArray *)fileTypes; //mp3, ogg, etc
++ (float)priority; // should be 0.0 ... 1.0, higher means you get selected first, should default to 1.0 unless you know a reason why any of your extensions may behave badly, ie. greedily taking over some file type extension without performing any header validation on it
 
 //For KVO
 //- (void)setProperties:(NSDictionary *)p;

Audio/PluginController.m

@@ -1,5 +1,6 @@
 #import "PluginController.h"
 #import "Plugin.h"
+#import "CogDecoderMulti.h"
 
 #import "Logging.h"
 
@@ -129,7 +130,16 @@ static PluginController *sharedPluginController = nil;
 	if (decoder && [decoder respondsToSelector:@selector(fileTypes)]) {
 		for (id fileType in [decoder fileTypes])
 		{
-			[decodersByExtension setObject:className forKey:[fileType lowercaseString]];
+            NSString *ext = [fileType lowercaseString];
+            NSMutableArray *decoders;
+            if (![decodersByExtension objectForKey:ext])
+            {
+                decoders = [[[NSMutableArray alloc] init] autorelease];
+                [decodersByExtension setObject:decoders forKey:ext];
+            }
+            else
+                decoders = [decodersByExtension objectForKey:ext];
+			[decoders addObject:className];
 		}
 	}
 	
@@ -216,8 +226,17 @@ static PluginController *sharedPluginController = nil;
 - (id<CogDecoder>) audioDecoderForSource:(id <CogSource>)source
 {
 	NSString *ext = [[[source url] path] pathExtension];
-	NSString *classString = [decodersByExtension objectForKey:[ext lowercaseString]];
-	if (!classString) {
+	NSArray *decoders = [decodersByExtension objectForKey:[ext lowercaseString]];
+    NSString *classString;
+    if (decoders) {
+        if ( [decoders count] > 1 ) {
+            return [[[CogDecoderMulti alloc] initWithDecoders:decoders] autorelease];
+        }
+        else {
+            classString = [decoders objectAtIndex:0];
+        }
+    }
+	else {
 		classString = [decodersByMimeType objectForKey:[[source mimeType] lowercaseString]];
 	}
 

Plugins/APL/APLDecoder.m

@@ -13,6 +13,10 @@
 	return [NSArray arrayWithObjects:@"application/x-apl", nil];
 }
 
++ (float)priority {
+    return 1.0;
+}
+
 - (NSDictionary *)properties {
 	NSMutableDictionary *properties = [[decoder properties] mutableCopy];
 	

Plugins/CoreAudio/CoreAudioDecoder.m

@@ -181,6 +181,11 @@
 	return nil;
 }
 
++ (float)priority
+{
+    return 0.5;
+}
+
 - (NSDictionary *)properties
 {
 	return [NSDictionary dictionaryWithObjectsAndKeys:

Plugins/CueSheet/CueSheetDecoder.m

@@ -26,6 +26,11 @@
 	return [CueSheetContainer mimeTypes];
 }
 
++ (float)priority
+{
+    return 1.0;
+}
+
 - (NSDictionary *)properties 
 {
 	NSMutableDictionary *properties = [[decoder properties] mutableCopy];

Plugins/Dumb/DumbDecoder.m

@@ -327,4 +327,9 @@ int callbackLoop(void *data)
 	return [NSArray arrayWithObjects:@"audio/x-it", @"audio/x-xm", @"audio/x-s3m", @"audio/x-mod", nil];
 }
 
++ (float)priority
+{
+    return 1.0;
+}
+
 @end

Plugins/FFMPEG/FFMPEGDecoder.m

@@ -327,6 +327,10 @@ int lockmgr_callback(void ** mutex, enum AVLockOp op)
 	return [NSArray arrayWithObjects:@"application/wma", @"application/x-wma", @"audio/x-wma", @"audio/x-ms-wma", @"audio/x-tak", @"audio/mpeg", @"audio/x-mp3", @"audio/x-mp2", @"audio/x-ape", @"audio/x-ac3", @"audio/x-dts", @"audio/x-dtshd", @"audio/x-at3", @"audio/wav", @"tta", nil];
 }
 
++ (float)priority
+{
+    return 1.0;
+}
 
 
 

Plugins/Flac/FlacDecoder.m

@@ -329,4 +329,9 @@ void ErrorCallback(const FLAC__StreamDecoder *decoder, FLAC__StreamDecoderErrorS
 	return [NSArray arrayWithObjects:@"audio/x-flac", nil];
 }
 
++ (float)priority
+{
+    return 1.0;
+}
+
 @end

Plugins/GME/GameDecoder.m

@@ -175,6 +175,11 @@ gme_err_t readCallback( void* data, void* out, long count )
 	return nil;
 }
 
++ (float)priority
+{
+    return 1.0;
+}
+
 - (void)setSource:(id<CogSource>)s
 {
 	[s retain];

Plugins/HighlyComplete/HighlyComplete/HCDecoder.mm

@@ -1531,6 +1531,10 @@ static int twosf_info(void * context, const char * name, const char * value)
 	return [NSArray arrayWithObjects:@"audio/x-psf", nil];
 }
 
++ (float)priority
+{
+    return 1.0;
+}
 
 
 @end

Plugins/MIDI/MIDI/MIDIDecoder.mm

@@ -175,4 +175,9 @@
 	return [NSArray arrayWithObjects:@"audio/midi", @"audio/x-midi", nil];
 }
 
++ (float)priority
+{
+    return 1.0;
+}
+
 @end

Plugins/Musepack/MusepackDecoder.m

@@ -228,4 +228,9 @@ mpc_bool_t CanSeekProc(void *data)
 	return [NSArray arrayWithObjects:@"audio/x-musepack", nil];
 }
 
++ (float)priority
+{
+    return 1.0;
+}
+
 @end

Plugins/Opus/Opus/OpusDecoder.m

@@ -160,4 +160,9 @@ opus_int64 sourceTell(void *_stream)
 	return [NSArray arrayWithObjects:@"audio/x-opus+ogg", nil];
 }
 
++ (float)priority
+{
+    return 1.0;
+}
+
 @end

Plugins/Shorten/ShortenDecoder.mm

@@ -103,5 +103,10 @@
 	return [NSArray arrayWithObjects:@"application/x-shorten", nil]; //This is basically useless, since we cant stream shorten yet
 }
 
++ (float)priority
+{
+    return 1.0;
+}
+
 
 @end

Plugins/Vorbis/VorbisDecoder.m

@@ -154,4 +154,9 @@ long sourceTell(void *datasource)
 	return [NSArray arrayWithObjects:@"application/ogg", @"application/x-ogg", @"audio/x-vorbis+ogg", nil];
 }
 
++ (float)priority
+{
+    return 1.0;
+}
+
 @end

Plugins/WavPack/WavPackDecoder.m

@@ -264,5 +264,10 @@ int32_t WriteBytesProc(void *ds, void *data, int32_t bcount)
 	return [NSArray arrayWithObjects:@"audio/x-wavpack", nil];
 }
 
++ (float)priority
+{
+    return 1.0;
+}
+
 
 @end