VGM Codec: Improve time and fade behavior. Tweak minor misc.

Prevents cutoff of tracks, especially short ones:
* Extend looped tracks by fade length to fade at start of loop repeat.
* No fade occurs for non-repeating track only having an intro.
* Uses id3.tail_trim field to store fade duration.

Use libGME built-in elapsed time reporting instead of custom calculation:
* libGME already reports in milliseconds.
* Don't advance time counter when Repeat == One. It just runs the progress
  over the length limit.

Fix a comment about sample rate and set the reported bitrate to be
accurate for 44.1 kHz stereo.

Change-Id: I3ede22bda0f9a941a3fef751f4d678eb0027344c

2 files changed, 40 insertions, 20 deletions

diff --git a/lib/rbcodec/codecs/vgm.c b/lib/rbcodec/codecs/vgm.c
index 416f772f1d..9f2f1b9c5e 100644
--- a/lib/rbcodec/codecs/vgm.c
+++ b/lib/rbcodec/codecs/vgm.c
@@ -23,6 +23,31 @@ static char *songbuf;               /* destination for uncompressed song */
 static uint32_t songbuflen=0;  /* size of the song buffer */
 static uint32_t songlen=0;       /* used size of the song buffer */
 
+static void codec_vgz_update_length(void)
+{
+    ci->id3->length = Track_get_length( &vgm_emu );
+    ci->id3->tail_trim = 4 * 1000;
+
+    if (vgm_emu.info.loop_length <= 0)
+        ci->id3->tail_trim = 0;
+
+    ci->id3->length += ci->id3->tail_trim;
+}
+
+static void codec_update_fade(void)
+{
+    /* for REPEAT_ONE we disable track limits */
+    Track_set_fade(&vgm_emu,
+                   ci->loop_track() ? indefinite_count :
+                        ci->id3->length - ci->id3->tail_trim,
+                   ci->id3->tail_trim);
+}
+
+static void codec_update_elapsed(void)
+{
+    ci->set_elapsed(ci->loop_track() ? 0 : Track_tell(&vgm_emu));
+}
+
 /****************** rockbox interface ******************/
 
 /* this is the codec entry point */
@@ -32,7 +57,7 @@ enum codec_status codec_main(enum codec_entry_call_reason reason)
         /* we only render 16 bits */
         ci->configure(DSP_SET_SAMPLE_DEPTH, 16);
 
-        /* 32 Khz, Interleaved stereo */
+        /* 44 Khz, Interleaved stereo */
         ci->configure(DSP_SET_FREQUENCY, 44100);
         ci->configure(DSP_SET_STEREO_MODE, STEREO_INTERLEAVED);
 
@@ -51,8 +76,6 @@ enum codec_status codec_run(void)
     size_t n;
     intptr_t param;
 
-    uint32_t elapsed_time = 0;
-
     DEBUGF("VGM: next_track\n");
     if (codec_init()) {
         return CODEC_ERROR;
@@ -95,7 +118,7 @@ enum codec_status codec_run(void)
 
         /* Since metadata parser doesn't support VGZ 
              will set song length here */
-        ci->id3->length = Track_get_length( &vgm_emu );
+        codec_vgz_update_length();
     }
     else if ((err = Vgm_load_mem(&vgm_emu, buf, n, false))) {
         DEBUGF("VGM: Vgm_load failed_mem (%s)\n", err);
@@ -104,12 +127,8 @@ enum codec_status codec_run(void)
 
     Vgm_start_track(&vgm_emu); 
 
-    /* for REPEAT_ONE we disable track limits */
-    if (!ci->loop_track()) {
-        Track_set_fade(&vgm_emu, ci->id3->length - 4000, 4000);
-    }
-    
     ci->set_elapsed(0);
+    codec_update_fade();
 
     /* The main decoder loop */
     while (1) {
@@ -119,23 +138,20 @@ enum codec_status codec_run(void)
             break;
 
         if (action == CODEC_ACTION_SEEK_TIME) {
-            ci->set_elapsed(param);
-            elapsed_time = param;
             Track_seek(&vgm_emu, param);
+            codec_update_elapsed();
             ci->seek_complete();
             
             /* Set fade again in case we seek to start of song */
-            Track_set_fade(&vgm_emu, ci->id3->length - 4000, 4000);
+            codec_update_fade();
         }
 
         /* Generate audio buffer */
         err = Vgm_play(&vgm_emu, CHUNK_SIZE, samples);
         if (err || Track_ended(&vgm_emu)) break;
 
-        ci->pcmbuf_insert(samples, NULL, CHUNK_SIZE >> 1);
-
-        elapsed_time += (CHUNK_SIZE / 2) * 10 / 441;
-        ci->set_elapsed(elapsed_time);
+        ci->pcmbuf_insert(samples, NULL, CHUNK_SIZE / 2);
+        codec_update_elapsed();
     }
 
     return CODEC_OK;
diff --git a/lib/rbcodec/metadata/vgm.c b/lib/rbcodec/metadata/vgm.c
index 7d3f45e204..03afb15a92 100644
--- a/lib/rbcodec/metadata/vgm.c
+++ b/lib/rbcodec/metadata/vgm.c
@@ -113,6 +113,8 @@ static long check_gd3_header( byte* h, long remain )
 static void get_vgm_length( struct header_t* h, struct mp3entry* id3 )
 {
     long length = get_long_le( h->track_duration ) * 10 / 441;
+    id3->tail_trim = 4 * 1000; /* assume fade */
+
     if ( length > 0 )
     {
         long loop_length = 0, intro_length = 0;
@@ -126,13 +128,15 @@ static void get_vgm_length( struct header_t* h, struct mp3entry* id3 )
         {
             intro_length = length; /* make it clear that track is no longer than length */
             loop_length = 0;
+            id3->tail_trim = 0;
         }
         
-         id3->length = intro_length + 2 * loop_length; /* intro + 2 loops */
-         return;
+        /* intro + 2 loops + fade */
+        id3->length = intro_length + 2 * loop_length + id3->tail_trim;
+        return;
     }
 
-    id3->length = 150 * 1000; /* 2.5 minutes */
+    id3->length = 150 * 1000 + id3->tail_trim; /* 2.5 minutes + fade */
 }
 
 bool get_vgm_metadata(int fd, struct mp3entry* id3)
@@ -151,7 +155,7 @@ bool get_vgm_metadata(int fd, struct mp3entry* id3)
     id3->vbr = false;
     id3->filesize = filesize(fd);
 
-    id3->bitrate = 706;
+    id3->bitrate = 1411;
     id3->frequency = 44100;
 
     /* If file is gzipped, will get metadata later */