AAC: Add support for iTunes-style gapless playback.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@13636 a1c6a512-1295-4272-9138-f99709370657

apps/codecs/aac.c

@@ -42,6 +42,8 @@ enum codec_status codec_main(void)
     uint32_t sample_duration;
     uint32_t sample_byte_size;
     int file_offset;
+    int framelength;
+    int lead_trim = 0;
     unsigned int i;
     unsigned char* buffer;
     static NeAACDecFrameInfo frame_info;
@@ -117,6 +119,11 @@ next_track:
             sound_samples_done = 0;
         }
     }
+    
+    if (i == 0) 
+    {
+        lead_trim = ci->id3->lead_trim;
+    }
 
     /* The main decoding loop */
     while (i < demux_res.num_sample_byte_sizes) {
@@ -133,6 +140,11 @@ next_track:
                           &sound_samples_done, (int*) &i)) {
                 elapsed_time = (sound_samples_done * 10) / (ci->id3->frequency / 100);
                 ci->set_elapsed(elapsed_time);
+            
+                if (i == 0) 
+                {
+                    lead_trim = ci->id3->lead_trim;
+                }
             }
             ci->seek_complete();
         }
@@ -183,8 +195,46 @@ next_track:
 
         /* Output the audio */
         ci->yield();
-        ci->pcmbuf_insert(decoder->time_out[0], decoder->time_out[1],
-                          frame_info.samples >> 1);
+        
+        framelength = (frame_info.samples >> 1) - lead_trim;
+        
+        if (i == demux_res.num_sample_byte_sizes - 1 && framelength > 0)
+        {
+            /* Currently limited to at most one frame of tail_trim.
+             * Seems to be enough.
+             */
+            if (ci->id3->tail_trim == 0 
+                && sample_duration < (frame_info.samples >> 1))
+            {
+                /* Subtract lead_trim just in case we decode a file with
+                 * only one audio frame with actual data.
+                 */
+                framelength = sample_duration - lead_trim;
+            }
+            else
+            {
+                framelength -= ci->id3->tail_trim;
+            }
+        }
+
+        if (framelength > 0)
+        {
+            ci->pcmbuf_insert(&decoder->time_out[0][lead_trim],
+                              &decoder->time_out[1][lead_trim],
+                              framelength);
+        } 
+        
+        if (lead_trim > 0)
+        {
+            /* frame_info.samples can be 0 for the first frame */
+            lead_trim -= (i > 0 || frame_info.samples)
+                ? (frame_info.samples >> 1) : sample_duration;
+
+            if (lead_trim < 0 || ci->id3->lead_trim == 0)
+            {
+                lead_trim = 0;
+            }
+        }
 
         /* Update the elapsed-time indicator */
         sound_samples_done += sample_duration;

apps/metadata.c

@@ -206,6 +206,43 @@ static long get_slong(void* buf)
 
     return p[0] | (p[1] << 8) | (p[2] << 16) | (p[3] << 24);
 }
+
+static char* skip_space(char* str)
+{
+    while (isspace(*str)) 
+    {
+        str++;
+    }
+    
+    return str;
+}
+
+static unsigned long get_itunes_int32(char* value, int count)
+{
+    static const char hexdigits[] = "0123456789ABCDEF";
+    const char* c;
+    int r = 0;
+    
+    while (count-- > 0)
+    {
+        value = skip_space(value);
+        
+        while (*value && !isspace(*value))
+        {
+            value++;
+        }
+    }
+    
+    value = skip_space(value);
+    
+    while (*value && ((c = strchr(hexdigits, toupper(*value))) != NULL))
+    {
+        r = (r << 4) | (c - hexdigits);
+        value++;
+    }
+    
+    return r;
+}
  
 /* Parse the tag (the name-value pair) and fill id3 and buffer accordingly.
  * String values to keep are written to buf. Returns number of bytes written
@@ -1520,6 +1557,19 @@ static bool read_mp4_tags(int fd, struct mp3entry* id3,
                 {
                     read_mp4_tag_string(fd, size, &buffer, &buffer_left, 
                         &id3->composer);
+                }   
+                else if (strcasecmp(tag_name, "iTunSMPB") == 0)
+                {
+                    char value[TAG_VALUE_LENGTH];
+                    char* value_p = value;
+                    char* any;
+                    unsigned int length = sizeof(value);
+
+                    read_mp4_tag_string(fd, size, &value_p, &length, &any);
+                    id3->lead_trim = get_itunes_int32(value, 1);
+                    id3->tail_trim = get_itunes_int32(value, 2);
+                    DEBUGF("AAC: lead_trim %d, tail_trim %d\n", 
+                        id3->lead_trim, id3->tail_trim);
                 }
                 else
                 {