Changeset 1010

Timestamp:

10/17/07 09:46:17 (15 months ago)

Author:

stephen_booth

Message:

Added an option for sample-accurate seeking

Files:

• trunk/Audio/Decoders/MPEGDecoder.m (modified) (4 diffs)

trunk/Audio/Decoders/MPEGDecoder.m

@@ -27 +27 @@
 
 #define INPUT_BUFFER_SIZE       (5 * 8192)
+#define SEEK_BUFFER_SIZE        1024
 #define LAME_HEADER_SIZE        ((8 * 5) + 4 + 4 + 8 + 32 + 16 + 16 + 4 + 4 + 8 + 12 + 12 + 8 + 8 + 2 + 3 + 11 + 32 + 32 + 32)
 
@@ -82 +83 @@
 @interface MPEGDecoder (Private)
 - (BOOL) scanFile;
+- (SInt64) seekToFrameApproximately:(SInt64)frame;
+- (SInt64) seekToFrameAccurately:(SInt64)frame;
 @end
 
@@ -175 +178 @@
 - (BOOL)                        supportsSeeking                                 { return YES; }
 
-        // FIXME: Seeking breaks gapless playback for the stream
 - (SInt64) seekToFrame:(SInt64)frame
 {
-        double  fraction        = (double)frame / [self totalFrames];
-        long    seekPoint       = 0;
-        
-        // If a Xing header was found, interpolate in TOC
-        if(_foundXingHeader) {
-                double          percent         = 100 * fraction;
-                unsigned        firstIndex      = percent;
-                
-                if(99 < firstIndex)
-                        firstIndex = 99;
-                
-                double firstOffset      = _xingTOC[firstIndex];
-                double secondOffset     = 256;
-                
-                if(99 > firstIndex)
-                        secondOffset = _xingTOC[firstIndex + 1];;
-                        
-                        double x = firstOffset + (secondOffset - firstOffset) * (percent - firstIndex);
-                        seekPoint = (long)((1.0 / 256.0) * x * _fileBytes); 
-        }
+        if([[NSUserDefaults standardUserDefaults] boolForKey:@"accurateMP3Seeking"])
+                return [self seekToFrameAccurately:frame];
         else
-                seekPoint = (long)_fileBytes * fraction;
-        
-        int result = fseek(_file, seekPoint, SEEK_SET);
-        if(0 == result) {
-                mad_stream_buffer(&_mad_stream, NULL, 0);
-                
-                // Reset frame count to prevent early termination of playback
-                _mpegFramesDecoded                      = 0;
-                _samplesDecoded                         = 0;
-                _samplesToSkipInNextFrame       = 0;
-                
-                _currentFrame                           = frame;
-        }
-        
-        // Right now it's only possible to return an approximation of the audio frame
-        return (-1 == result ? -1 : frame);
+                return [self seekToFrameApproximately:frame];
 }
 
@@ -686 +655 @@
 }
 
+- (SInt64) seekToFrameApproximately:(SInt64)frame
+{
+        double  fraction        = (double)frame / [self totalFrames];
+        long    seekPoint       = 0;
+        
+        // If a Xing header was found, interpolate in TOC
+        if(_foundXingHeader) {
+                double          percent         = 100 * fraction;
+                unsigned        firstIndex      = percent;
+                
+                if(99 < firstIndex)
+                        firstIndex = 99;
+                
+                double firstOffset      = _xingTOC[firstIndex];
+                double secondOffset     = 256;
+                
+                if(99 > firstIndex)
+                        secondOffset = _xingTOC[firstIndex + 1];;
+                        
+                        double x = firstOffset + (secondOffset - firstOffset) * (percent - firstIndex);
+                        seekPoint = (long)((1.0 / 256.0) * x * _fileBytes); 
+        }
+        else
+                seekPoint = (long)_fileBytes * fraction;
+        
+        int result = fseek(_file, seekPoint, SEEK_SET);
+        if(0 == result) {
+                mad_stream_buffer(&_mad_stream, NULL, 0);
+                
+                // Reset frame count to prevent early termination of playback
+                _mpegFramesDecoded                      = 0;
+                _samplesDecoded                         = 0;
+                _samplesToSkipInNextFrame       = 0;
+                
+                _currentFrame                           = frame;
+        }
+        
+        // Right now it's only possible to return an approximation of the audio frame
+        return (-1 == result ? -1 : frame);
+}
+
+- (SInt64) seekToFrameAccurately:(SInt64)frame
+{
+        NSParameterAssert(0 <= frame && frame < [self totalFrames]);
+        
+        // Brute-force seeking is necessary since frame-accurate seeking is required
+        
+        // To seek to a frame earlier in the file, rewind to the beginning
+        if([self currentFrame] > frame) {
+                if(-1 == fseek(_file, 0, SEEK_SET))
+                        return -1;
+                
+                // Reset decoder parameters
+                _mpegFramesDecoded                      = 0;
+                _currentFrame                           = 0;
+                _samplesToSkipInNextFrame       = 0;
+                _samplesDecoded                         = 0;
+                
+                // Zero the buffers
+                unsigned i;
+                for(i = 0; i < _bufferList->mNumberBuffers; ++i)
+                        _bufferList->mBuffers[i].mDataByteSize = 0;
+                
+                mad_stream_buffer(&_mad_stream, NULL, 0);
+        }
+        
+        // Allocate a buffer list to use for seeking
+        AudioBufferList *bufferList = calloc(sizeof(AudioBufferList) + (sizeof(AudioBuffer) * (_format.mChannelsPerFrame - 1)), 1);
+        NSAssert(NULL != bufferList, @"Unable to allocate memory");
+        
+        bufferList->mNumberBuffers = _format.mChannelsPerFrame;
+        
+        unsigned i;
+        for(i = 0; i < bufferList->mNumberBuffers; ++i) {
+                bufferList->mBuffers[i].mData = calloc(SEEK_BUFFER_SIZE, sizeof(float));
+                NSAssert(NULL != bufferList->mBuffers[i].mData, @"Unable to allocate memory");
+                
+                bufferList->mBuffers[i].mNumberChannels = 1;
+        }
+        
+        // Decode until the desired frame is reached            
+        for(;;) {
+                UInt32 framesRemaining  = frame - [self currentFrame];
+                UInt32 framesToRead             = (SEEK_BUFFER_SIZE > framesRemaining ? framesRemaining : SEEK_BUFFER_SIZE);;
+                
+                if(0 == framesRemaining)
+                        break;
+                
+                UInt32 framesRead = [self readAudio:bufferList frameCount:framesToRead];
+                if(0 == framesRead)
+                        break;
+        }
+        
+        for(i = 0; i < bufferList->mNumberBuffers; ++i)
+                free(bufferList->mBuffers[i].mData), bufferList->mBuffers[i].mData = NULL;      
+        free(bufferList), bufferList = NULL;
+        
+        return [self currentFrame];
+}
+
 @end