Patch from bug report #5200 by Mark Arigo - attempt to fix gapless playback after seeking in an MP3 file. It works for me, but needs more testing with a wider range of files before we can close the bug report - please post feedback on the tracker.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@9962 a1c6a512-1295-4272-9138-f99709370657

1 files changed, 75 insertions, 88 deletions

diff --git a/apps/codecs/mpa.c b/apps/codecs/mpa.c
index 4c3784a..81604de 100644
--- a/apps/codecs/mpa.c
+++ b/apps/codecs/mpa.c
@@ -40,6 +40,7 @@ mad_fixed_t mad_frame_overlap[2][32][18] IBSS_ATTR;
 unsigned char mad_main_data[MAD_BUFFER_MDLEN] IBSS_ATTR;
 /* TODO: what latency does layer 1 have? */
 int mpeg_latency[3] = { 0, 481, 529 };
+int mpeg_framesize[3] = {384, 1152, 1152};
 
 #ifdef USE_IRAM
 extern char iramcopy[];
@@ -50,34 +51,13 @@ extern char iend[];
 #endif
 
 struct codec_api *ci;
-int64_t samplecount;
-int64_t samplesdone;
-int stop_skip, start_skip;
-int current_stereo_mode = -1;
-unsigned long current_frequency = 0;
-
-void recalc_samplecount(void)
-{
-    /* NOTE: currently this doesn't work, the below calculated samples_count
-       seems to be right, but sometimes we just don't have all the data we
-       need... */
-    if (ci->id3->frame_count) {
-        /* TODO: 1152 is the frame size in samples for MPEG1 layer 2 and layer 3,
-           it's probably not correct at all for MPEG2 and layer 1 */
-        samplecount = ((int64_t)ci->id3->frame_count) * 1152;
-    } else {
-        samplecount = ((int64_t)ci->id3->length) * current_frequency / 1000;
-    }
-    
-    samplecount -= start_skip + stop_skip;
-}
 
 void init_mad(void)
 {
     ci->memset(&stream, 0, sizeof(struct mad_stream));
     ci->memset(&frame, 0, sizeof(struct mad_frame));
     ci->memset(&synth, 0, sizeof(struct mad_synth));
-    
+
     mad_stream_init(&stream);
     mad_frame_init(&frame);
     mad_synth_init(&synth);
@@ -94,14 +74,14 @@ enum codec_status codec_start(struct codec_api *api)
     int status;
     size_t size;
     int file_end;
-    int frame_skip;      /* samples to skip current frame */
     int samples_to_skip; /* samples to skip in total for this file (at start) */
     char *inputbuffer;
-    /* If we know the position isn't exact (i.e., we have seeked to a
-     * position that isn't the start of the file), we can't reliably do 
-     * end-of-file trimming for gapless playback.
-     */
-    bool exact_position = true;
+    int64_t samplesdone;
+    int stop_skip, start_skip;
+    int current_stereo_mode = -1;
+    unsigned long current_frequency = 0;
+    int framelength;
+    int padding = MAD_BUFFER_GUARD; /* to help mad decode the last frame */
 
     ci = api;
 
@@ -120,20 +100,17 @@ enum codec_status codec_start(struct codec_api *api)
     ci->configure(DSP_SET_CLIP_MIN, (int *)-MAD_F_ONE);
     ci->configure(DSP_SET_CLIP_MAX, (int *)(MAD_F_ONE - 1));
     ci->configure(CODEC_SET_FILEBUF_CHUNKSIZE, (int *)(1024*16));
-    
-    /** This label might need to be moved above all the init code, but I don't
-     * think reiniting the codec is necessary for MPEG. It might even be unwanted
-     * for gapless playback.
-     * Reinitializing seems to be necessary to avoid playback quircks when seeking. */
-    next_track:
+
+next_track:
     status = CODEC_OK;
-        
+
+    /* Reinitializing seems to be necessary to avoid playback quircks when seeking. */
     init_mad();
 
     file_end = 0;
     while (!*ci->taginfo_ready && !ci->stop_codec)
         ci->sleep(1);
-  
+
     ci->configure(DSP_SET_FREQUENCY, (int *)ci->id3->frequency);
     current_frequency = ci->id3->frequency;
     codec_set_replaygain(ci->id3);
@@ -151,35 +128,52 @@ enum codec_status codec_start(struct codec_api *api)
         start_skip = mpeg_latency[ci->id3->layer];
     }
 
+    /* Libmad will not decode the last frame without 8 bytes of extra padding
+       in the buffer. So, we can trick libmad into not decoding the last frame
+       if we are to skip it entirely and then cut the appropriate samples from
+       final frame that we did decode. Note, if all tags (ID3, APE) are not
+       properly stripped from the end of the file, this trick will not work. */
+    if (stop_skip >= mpeg_framesize[ci->id3->layer]) {
+        padding = 0;
+        stop_skip -= mpeg_framesize[ci->id3->layer];
+    } else {
+        padding = MAD_BUFFER_GUARD;
+    }
+
     samplesdone = ((int64_t)ci->id3->elapsed) * current_frequency / 1000;
-    exact_position = samplesdone == 0;
-    samples_to_skip = start_skip;
-    recalc_samplecount();
-    
+
+    /* Don't skip any samples unless we start at the beginning. */
+    if (samplesdone > 0)
+        samples_to_skip = 0;
+    else
+        samples_to_skip = start_skip;
+
+    framelength = 0;
+
     /* This is the decoding loop. */
     while (1) {
-        int framelength;
-
         ci->yield();
         if (ci->stop_codec || ci->new_track)
             break;
     
         if (ci->seek_time) {
             int newpos;
-        
-            samplesdone = ((int64_t) (ci->seek_time - 1)) 
-                * current_frequency / 1000;
-            exact_position = samplesdone == 0;
 
-            if (ci->seek_time-1 == 0)
+            samplesdone = ((int64_t)(ci->seek_time-1))*current_frequency/1000;
+
+            if (ci->seek_time-1 == 0) {
                 newpos = ci->id3->first_frame_offset;
-            else
+                samples_to_skip = start_skip;
+            } else {
                 newpos = ci->mp3_get_filepos(ci->seek_time-1);
+                samples_to_skip = 0;
+            }
 
             if (!ci->seek_buffer(newpos))
                 break;
             ci->seek_complete();
             init_mad();
+            framelength = 0;
         }
 
         /* Lock buffers */
@@ -187,18 +181,17 @@ enum codec_status codec_start(struct codec_api *api)
             inputbuffer = ci->request_buffer(&size, INPUT_CHUNK_SIZE);
             if (size == 0 || inputbuffer == NULL)
                 break;
-            /* size + MAD_BUFFER_GUARD to help mad decode the last frame */
             mad_stream_buffer(&stream, (unsigned char *)inputbuffer,
-                    size + MAD_BUFFER_GUARD);
+                              size + padding);
         }
-    
+
         if (mad_frame_decode(&frame, &stream)) {
             if (stream.error == MAD_FLAG_INCOMPLETE 
                 || stream.error == MAD_ERROR_BUFLEN) {
                 /* This makes the codec support partially corrupted files */
                 if (file_end == 30)
                     break;
-        
+
                 /* Fill the buffer */
                 if (stream.next_frame)
                     ci->advance_buffer_loc((void *)stream.next_frame);
@@ -216,39 +209,28 @@ enum codec_status codec_start(struct codec_api *api)
             }
             break;
         }
-        
+
         file_end = 0;
 
-        mad_synth_frame(&synth, &frame);
-        
-        /* We need to skip samples_to_skip samples from the start of every file
-           to properly support LAME style gapless MP3 files. samples_to_skip
-           might be larger than one frame. */
-        if (samples_to_skip < synth.pcm.length) {
-            /* skip just part of the frame */
-            frame_skip = samples_to_skip;
+        /* Do the pcmbuf insert here. Note, this is the PREVIOUS frame's pcm
+           data (not the one just decoded above). When we exit the decoding
+           loop we will need to process the final frame that was decoded. */
+        if (framelength > 0) {
+            /* In case of a mono file, the second array will be ignored. */
+            ci->pcmbuf_insert_split(&synth.pcm.samples[0][samples_to_skip],
+                                    &synth.pcm.samples[1][samples_to_skip],
+                                    framelength * 4);
+
+            /* Only skip samples for the first frame added. */
             samples_to_skip = 0;
-        } else {
-            /* we need to skip an entire frame */
-            frame_skip = synth.pcm.length;
-            samples_to_skip -= synth.pcm.length;
-        }
-       
-        framelength = synth.pcm.length - frame_skip;
-        
-        if (exact_position && (stop_skip > 0)) {
-            int64_t max = samplecount - samplesdone;
-            
-            if (max < 0) max = 0;
-            if (max < framelength) framelength = (int)max;
-            if (framelength == 0 && frame_skip == 0) break;
         }
-        
+
+        mad_synth_frame(&synth, &frame);
+
         /* Check if sample rate and stereo settings changed in this frame. */
         if (frame.header.samplerate != current_frequency) {
             current_frequency = frame.header.samplerate;
             ci->configure(DSP_SWITCH_FREQUENCY, (int *)current_frequency);
-            recalc_samplecount();
         }
         if (MAD_NCHANNELS(&frame.header) == 2) {
             if (current_stereo_mode != STEREO_NONINTERLEAVED) {
@@ -261,27 +243,32 @@ enum codec_status codec_start(struct codec_api *api)
                 current_stereo_mode = STEREO_MONO;
             }
         }
-      
-        /* Check if we can just skip the entire frame. */
-        if (frame_skip < synth.pcm.length) {
-            /* In case of a mono file, the second array will be ignored. */
-            ci->pcmbuf_insert_split(&synth.pcm.samples[0][frame_skip],
-                                    &synth.pcm.samples[1][frame_skip],
-                                    framelength * 4);
-        }
-        
+
         if (stream.next_frame)
             ci->advance_buffer_loc((void *)stream.next_frame);
         else
             ci->advance_buffer(size);
 
+        framelength = synth.pcm.length - samples_to_skip;
+        if (framelength < 0) {
+            framelength = 0;
+            samples_to_skip -= synth.pcm.length;
+        }
+
         samplesdone += framelength;
         ci->set_elapsed(samplesdone / (current_frequency / 1000));
     }
+
+    /* Finish the remaining decoded frame.
+       Cut the required samples from the end. */
+    if (framelength > stop_skip)
+        ci->pcmbuf_insert_split(synth.pcm.samples[0], synth.pcm.samples[1],
+                                (framelength - stop_skip) * 4);
+
     stream.error = 0;
-  
+
     if (ci->request_next_track())
         goto next_track;
-    
+
     return status;
 }