AAC codec: Improved MP4 file parsing. Should now handle most streamable files. Also some code cleanup and policing.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@11187 a1c6a512-1295-4272-9138-f99709370657

3 files changed, 373 insertions, 194 deletions

diff --git a/apps/codecs/libm4a/demux.c b/apps/codecs/libm4a/demux.c
index 1beeced8e6..44261fdef6 100644
--- a/apps/codecs/libm4a/demux.c
+++ b/apps/codecs/libm4a/demux.c
@@ -55,12 +55,14 @@ static void read_chunk_ftyp(qtmovie_t *qtmovie, size_t chunk_len)
 {
     fourcc_t type;
     uint32_t minor_ver;
-    size_t size_remaining = chunk_len - 8; /* FIXME: can't hardcode 8, size may be 64bit */
+    size_t size_remaining = chunk_len - 8;
 
     type = stream_read_uint32(qtmovie->stream);
     size_remaining-=4;
     if ((type != MAKEFOURCC('M','4','A',' ')) &&
-        (type != MAKEFOURCC('m','p','4','2')))
+        (type != MAKEFOURCC('m','p','4','2')) &&
+        (type != MAKEFOURCC('3','g','p','6')) &&
+        (type != MAKEFOURCC('q','t',' ',' ')))
     {
         DEBUGF("not M4A file\n");
         return;
@@ -80,7 +82,7 @@ static void read_chunk_ftyp(qtmovie_t *qtmovie, size_t chunk_len)
 static void read_chunk_tkhd(qtmovie_t *qtmovie, size_t chunk_len)
 {
     /* don't need anything from here atm, skip */
-    size_t size_remaining = chunk_len - 8; /* FIXME WRONG */
+    size_t size_remaining = chunk_len - 8;
 
     stream_skip(qtmovie->stream, size_remaining);
 }
@@ -88,7 +90,7 @@ static void read_chunk_tkhd(qtmovie_t *qtmovie, size_t chunk_len)
 static void read_chunk_mdhd(qtmovie_t *qtmovie, size_t chunk_len)
 {
     /* don't need anything from here atm, skip */
-    size_t size_remaining = chunk_len - 8; /* FIXME WRONG */
+    size_t size_remaining = chunk_len - 8;
 
     stream_skip(qtmovie->stream, size_remaining);
 }
@@ -97,7 +99,7 @@ static void read_chunk_mdhd(qtmovie_t *qtmovie, size_t chunk_len)
 static void read_chunk_hdlr(qtmovie_t *qtmovie, size_t chunk_len)
 {
     fourcc_t comptype, compsubtype;
-    size_t size_remaining = chunk_len - 8; /* FIXME WRONG */
+    size_t size_remaining = chunk_len - 8;
 
     int strlen;
     char str[256] = {0};
@@ -196,7 +198,6 @@ static bool read_chunk_esds(qtmovie_t *qtmovie, size_t chunk_len)
     temp=stream_read_int32(qtmovie->stream);//0x15000414 ????
     maxBitrate = stream_read_int32(qtmovie->stream);
     avgBitrate = stream_read_int32(qtmovie->stream);
-
     DEBUGF("audioType=%d, maxBitrate=%d, avgBitrate=%d\n",audioType,maxBitrate,avgBitrate);
 
     /* get and verify DecSpecificInfoTag */
@@ -224,7 +225,7 @@ static bool read_chunk_stsd(qtmovie_t *qtmovie, size_t chunk_len)
     unsigned int i;
     int j;
     uint32_t numentries;
-    size_t size_remaining = chunk_len - 8; /* FIXME WRONG */
+    size_t size_remaining = chunk_len - 8;
 
     /* version */
     stream_read_uint8(qtmovie->stream);
@@ -247,7 +248,6 @@ static bool read_chunk_stsd(qtmovie_t *qtmovie, size_t chunk_len)
     for (i = 0; i < numentries; i++)
     {
         uint32_t entry_size;
-        uint16_t version;
 
         uint32_t entry_remaining;
 
@@ -259,43 +259,20 @@ static bool read_chunk_stsd(qtmovie_t *qtmovie, size_t chunk_len)
 
         /* sound info: */
 
-        stream_skip(qtmovie->stream, 6); /* reserved */
-        entry_remaining -= 6;
-
-        version = stream_read_uint16(qtmovie->stream);
-        //       if (version != 1)
-            //fprintf(stderr, "unknown version??\n");
-        entry_remaining -= 2;
-
-        /* revision level */
-        stream_read_uint16(qtmovie->stream);
-        /* vendor */
-        stream_read_uint32(qtmovie->stream);
-        entry_remaining -= 6;
-
-        /* EH?? spec doesn't say theres an extra 16 bits here.. but there is! */
-        stream_read_uint16(qtmovie->stream);
-        entry_remaining -= 2;
+        /* reserved + data reference index + sound version + reserved */
+        stream_skip(qtmovie->stream, 6 + 2 + 2 + 6);
+        entry_remaining -= 6 + 2 + 2 + 6;
 
         qtmovie->res->num_channels = stream_read_uint16(qtmovie->stream);
-
-        qtmovie->res->sample_size = stream_read_uint16(qtmovie->stream);
+        qtmovie->res->sound_sample_size = stream_read_uint16(qtmovie->stream);
         entry_remaining -= 4;
 
-        /* compression id */
-        stream_read_uint16(qtmovie->stream);
         /* packet size */
-        stream_read_uint16(qtmovie->stream);
-        entry_remaining -= 4;
-
-        /* sample rate - 32bit fixed point = 16bit?? */
-        qtmovie->res->sample_rate = stream_read_uint16(qtmovie->stream);
-        entry_remaining -= 2;
-
-        /* skip 2 */
         stream_skip(qtmovie->stream, 2);
-        entry_remaining -= 2;
-
+        qtmovie->res->sound_sample_rate = stream_read_uint32(qtmovie->stream);
+        /* reserved size */
+        stream_skip(qtmovie->stream, 2);
+        entry_remaining -= 8;
 
         /* remaining is codec data */
 
@@ -372,7 +349,7 @@ static void read_chunk_stts(qtmovie_t *qtmovie, size_t chunk_len)
 {
     unsigned int i;
     uint32_t numentries;
-    size_t size_remaining = chunk_len - 8; /* FIXME WRONG */
+    size_t size_remaining = chunk_len - 8;
 
     /* version */
     stream_read_uint8(qtmovie->stream);
@@ -407,7 +384,7 @@ static void read_chunk_stsz(qtmovie_t *qtmovie, size_t chunk_len)
 {
     unsigned int i;
     uint32_t numentries;
-    size_t size_remaining = chunk_len - 8; /* FIXME WRONG */
+    size_t size_remaining = chunk_len - 8;
 
     /* version */
     stream_read_uint8(qtmovie->stream);
@@ -447,9 +424,73 @@ static void read_chunk_stsz(qtmovie_t *qtmovie, size_t chunk_len)
     }
 }
 
+static void read_chunk_stsc(qtmovie_t *qtmovie, size_t chunk_len)
+{
+    unsigned int i;
+    uint32_t numentries;
+    size_t size_remaining = chunk_len - 8;
+
+    /* version + flags */
+    stream_read_uint32(qtmovie->stream);
+    size_remaining -= 4;
+
+    numentries = stream_read_uint32(qtmovie->stream);
+    size_remaining -= 4;
+
+    qtmovie->res->num_sample_to_chunks = numentries;
+    qtmovie->res->sample_to_chunk = malloc(numentries *
+        sizeof(*qtmovie->res->sample_to_chunk));
+
+    for (i = 0; i < numentries; i++)
+    {
+        qtmovie->res->sample_to_chunk[i].first_chunk = 
+            stream_read_uint32(qtmovie->stream);
+        qtmovie->res->sample_to_chunk[i].num_samples = 
+            stream_read_uint32(qtmovie->stream);
+        stream_read_uint32(qtmovie->stream);
+        size_remaining -= 12;
+    }
+
+    if (size_remaining)
+    {
+        DEBUGF("ehm, size remianing?\n");
+        stream_skip(qtmovie->stream, size_remaining);
+    }
+}
+
+static void read_chunk_stco(qtmovie_t *qtmovie, size_t chunk_len)
+{
+    unsigned int i;
+    uint32_t numentries;
+    size_t size_remaining = chunk_len - 8;
+
+    /* version + flags */
+    stream_read_uint32(qtmovie->stream);
+    size_remaining -= 4;
+
+    numentries = stream_read_uint32(qtmovie->stream);
+    size_remaining -= 4;
+
+    qtmovie->res->num_chunk_offsets = numentries;
+    qtmovie->res->chunk_offset = malloc(numentries * 
+        sizeof(*qtmovie->res->chunk_offset));
+
+    for (i = 0; i < numentries; i++)
+    {
+        qtmovie->res->chunk_offset[i] = stream_read_uint32(qtmovie->stream);
+        size_remaining -= 4;
+    }
+
+    if (size_remaining)
+    {
+        DEBUGF("ehm, size remianing?\n");
+        stream_skip(qtmovie->stream, size_remaining);
+    }
+}
+
 static bool read_chunk_stbl(qtmovie_t *qtmovie, size_t chunk_len)
 {
-    size_t size_remaining = chunk_len - 8; /* FIXME WRONG */
+    size_t size_remaining = chunk_len - 8;
 
     while (size_remaining)
     {
@@ -479,14 +520,15 @@ static bool read_chunk_stbl(qtmovie_t *qtmovie, size_t chunk_len)
             read_chunk_stsz(qtmovie, sub_chunk_len);
             break;
         case MAKEFOURCC('s','t','s','c'):
+            read_chunk_stsc(qtmovie, sub_chunk_len);
+            break;
         case MAKEFOURCC('s','t','c','o'):
-            /* skip these, no indexing for us! */
-            stream_skip(qtmovie->stream, sub_chunk_len - 8);
+            read_chunk_stco(qtmovie, sub_chunk_len);
             break;
         default:
             DEBUGF("(stbl) unknown chunk id: %c%c%c%c\n",
                    SPLITFOURCC(sub_chunk_id));
-            stream_skip(qtmovie->stream, sub_chunk_len - 8); /* FIXME not 8 */
+            stream_skip(qtmovie->stream, sub_chunk_len - 8);
         }
 
         size_remaining -= sub_chunk_len;
@@ -497,7 +539,7 @@ static bool read_chunk_stbl(qtmovie_t *qtmovie, size_t chunk_len)
 static bool read_chunk_minf(qtmovie_t *qtmovie, size_t chunk_len)
 {
     size_t dinf_size, stbl_size;
-    size_t size_remaining = chunk_len - 8; /* FIXME WRONG */
+    size_t size_remaining = chunk_len - 8;
     uint32_t i;
 
   /**** SOUND HEADER CHUNK ****/
@@ -553,7 +595,7 @@ static bool read_chunk_minf(qtmovie_t *qtmovie, size_t chunk_len)
 
 static bool read_chunk_mdia(qtmovie_t *qtmovie, size_t chunk_len)
 {
-    size_t size_remaining = chunk_len - 8; /* FIXME WRONG */
+    size_t size_remaining = chunk_len - 8;
 
     while (size_remaining)
     {
@@ -597,7 +639,7 @@ static bool read_chunk_mdia(qtmovie_t *qtmovie, size_t chunk_len)
 /* 'trak' - a movie track - contains other atoms */
 static bool read_chunk_trak(qtmovie_t *qtmovie, size_t chunk_len)
 {
-    size_t size_remaining = chunk_len - 8; /* FIXME WRONG */
+    size_t size_remaining = chunk_len - 8;
 
     while (size_remaining)
     {
@@ -639,7 +681,7 @@ static bool read_chunk_trak(qtmovie_t *qtmovie, size_t chunk_len)
 static void read_chunk_mvhd(qtmovie_t *qtmovie, size_t chunk_len)
 {
     /* don't need anything from here atm, skip */
-    size_t size_remaining = chunk_len - 8; /* FIXME WRONG */
+    size_t size_remaining = chunk_len - 8;
 
     stream_skip(qtmovie->stream, size_remaining);
 }
@@ -648,7 +690,7 @@ static void read_chunk_mvhd(qtmovie_t *qtmovie, size_t chunk_len)
 static void read_chunk_udta(qtmovie_t *qtmovie, size_t chunk_len)
 {
     /* don't need anything from here atm, skip */
-    size_t size_remaining = chunk_len - 8; /* FIXME WRONG */
+    size_t size_remaining = chunk_len - 8;
 
     stream_skip(qtmovie->stream, size_remaining);
 }
@@ -656,7 +698,7 @@ static void read_chunk_udta(qtmovie_t *qtmovie, size_t chunk_len)
 /* 'moov' movie atom - contains other atoms */
 static bool read_chunk_moov(qtmovie_t *qtmovie, size_t chunk_len)
 {
-    size_t size_remaining = chunk_len - 8; /* FIXME WRONG */
+    size_t size_remaining = chunk_len - 8;
 
     while (size_remaining)
     {
@@ -688,7 +730,7 @@ static bool read_chunk_moov(qtmovie_t *qtmovie, size_t chunk_len)
         default:
             DEBUGF("(moov) unknown chunk id: %c%c%c%c\n",
                     SPLITFOURCC(sub_chunk_id));
-            stream_skip(qtmovie->stream, sub_chunk_len - 8); /* FIXME not 8 */
+            stream_skip(qtmovie->stream, sub_chunk_len - 8);
         }
 
         size_remaining -= sub_chunk_len;
@@ -698,14 +740,9 @@ static bool read_chunk_moov(qtmovie_t *qtmovie, size_t chunk_len)
 
 static void read_chunk_mdat(qtmovie_t *qtmovie, size_t chunk_len)
 {
-    size_t size_remaining = chunk_len - 8; /* FIXME WRONG */
+    size_t size_remaining = chunk_len - 8;
 
     qtmovie->res->mdat_len = size_remaining;
-#if 0
-    qtmovie->res->mdat = malloc(size_remaining);
-
-    stream_read(qtmovie->stream, size_remaining, qtmovie->res->mdat);
-#endif
 }
 
 int qtmovie_read(stream_t *file, demux_res_t *demux_res)
@@ -760,7 +797,7 @@ int qtmovie_read(stream_t *file, demux_res_t *demux_res)
 
             /*  these following atoms can be skipped !!!! */
         case MAKEFOURCC('f','r','e','e'):
-            stream_skip(qtmovie.stream, chunk_len - 8); /* FIXME not 8 */
+            stream_skip(qtmovie.stream, chunk_len - 8);
             break;
         default:
             //DEBUGF("(top) unknown chunk id: %c%c%c%c\n",SPLITFOURCC(chunk_id));
diff --git a/apps/codecs/libm4a/m4a.c b/apps/codecs/libm4a/m4a.c
index f914f4e4d1..0a87ec35ea 100644
--- a/apps/codecs/libm4a/m4a.c
+++ b/apps/codecs/libm4a/m4a.c
@@ -21,6 +21,13 @@
 #include <inttypes.h>
 #include "m4a.h"
 
+#if defined(DEBUG) || defined(SIMULATOR)
+extern struct codec_api* rb;
+#define DEBUGF  rb->debugf
+#else
+#define DEBUGF(...)
+#endif
+
 /* Implementation of the stream.h functions used by libalac */
 
 #define _Swap32(v) do { \
@@ -101,15 +108,7 @@ uint8_t stream_read_uint8(stream_t *stream)
 
 void stream_skip(stream_t *stream, size_t skip)
 {
-  (void)stream;
-#if 1
-  char buf;
-  while (skip > 0) {
-    stream->ci->read_filebuf(&buf,1);
-    skip--;
-  }
-#endif
-  //stream->ci->advance_buffer(skip);
+  stream->ci->advance_buffer(skip);
 }
 
 int stream_eof(stream_t *stream)
@@ -158,136 +157,273 @@ int get_sample_info(demux_res_t *demux_res, uint32_t samplenum,
     return 1;
 }
 
-/* Seek to sample_loc (or close to it).  Return 1 on success (and
-   modify samplesdone and currentblock), 0 if failed 
+unsigned int get_sample_offset(demux_res_t *demux_res, uint32_t sample)
+{
+    uint32_t chunk = 1;
+    uint32_t range_samples = 0;
+    uint32_t total_samples = 0;
+    uint32_t chunk_sample;
+    uint32_t prev_chunk;
+    uint32_t prev_chunk_samples;
+    uint32_t file_offset;
+    uint32_t i;
+    
+    /* First check we have the appropriate metadata - we should always
+     * have it.
+     */
+       
+    if (sample >= demux_res->num_sample_byte_sizes ||
+        !demux_res->num_sample_to_chunks ||
+        !demux_res->num_chunk_offsets) 
+    {
+        return 0;
+    }
 
-   Seeking uses the following two arrays:
+    /* Locate the chunk containing the sample */
+    
+    prev_chunk = demux_res->sample_to_chunk[0].first_chunk;
+    prev_chunk_samples = demux_res->sample_to_chunk[0].num_samples;
 
-     1) the sample_byte_size array contains the length in bytes of
-        each block ("sample" in Applespeak).
+    for (i = 1; i < demux_res->num_sample_to_chunks; i++) 
+    {
+        chunk = demux_res->sample_to_chunk[i].first_chunk;
+        range_samples = (chunk - prev_chunk) * prev_chunk_samples;
 
-     2) the time_to_sample array contains the duration (in samples) of
-        each block of data.
+        if (sample < total_samples + range_samples)
+        {
+            break;
+        }
 
-     So we just find the block number we are going to seek to (using
-     time_to_sample) and then find the offset in the file (using
-     sample_byte_size).
+        total_samples += range_samples;
+        prev_chunk = demux_res->sample_to_chunk[i].first_chunk;
+        prev_chunk_samples = demux_res->sample_to_chunk[i].num_samples;
+    }
 
-     Each ALAC block seems to be independent of all the others.
- */
+    if (demux_res->num_sample_to_chunks > 1)
+    {
+        chunk = prev_chunk + (sample - total_samples) / prev_chunk_samples;
+    }
+    else
+    {
+        chunk = 1;
+    }
+    
+    /* Get sample of the first sample in the chunk */
+    
+    chunk_sample = total_samples + (chunk - prev_chunk) * prev_chunk_samples;
+    
+    /* Get offset in file */
+    
+    if (chunk > demux_res->num_chunk_offsets)
+    {
+        file_offset = demux_res->chunk_offset[demux_res->num_chunk_offsets - 1];
+    }
+    else
+    {
+        file_offset = demux_res->chunk_offset[chunk - 1];
+    }
+    
+    if (chunk_sample > sample) {
+        return 0;
+    }
+ 
+    for (i = chunk_sample; i < sample; i++)
+    {
+        file_offset += demux_res->sample_byte_size[i];
+    }
+    
+    if (file_offset > demux_res->mdat_offset + demux_res->mdat_len)
+    {
+        return 0;
+    }
+    
+    return file_offset;
+}
 
-unsigned int alac_seek (demux_res_t* demux_res, 
-                        stream_t* stream,
-                        unsigned int sample_loc, 
-                        uint32_t* samplesdone, int* currentblock)
+/* Seek to the sample containing sound_sample_loc. Return 1 on success 
+ * (and modify sound_samples_done and current_sample), 0 if failed.
+ *
+ * Seeking uses the following arrays:
+ *
+ * 1) the time_to_sample array contains the duration (in sound samples) 
+ *    of each sample of data.
+ *
+ * 2) the sample_byte_size array contains the length in bytes of each
+ *    sample.
+ *
+ * 3) the sample_to_chunk array contains information about which chunk
+ *    of samples each sample belongs to.
+ *
+ * 4) the chunk_offset array contains the file offset of each chunk.
+ *
+ * So find the sample number we are going to seek to (using time_to_sample)
+ * and then find the offset in the file (using sample_to_chunk, 
+ * chunk_offset sample_byte_size, in that order.).
+ *
+ */
+unsigned int alac_seek(demux_res_t* demux_res, stream_t* stream, 
+    uint32_t sound_sample_loc, uint32_t* sound_samples_done, 
+    int* current_sample)
 {
-  int flag;
-  unsigned int i,j;
-  unsigned int newblock;
-  unsigned int newsample;
-  unsigned int newpos;
-
-  /* First check we have the appropriate metadata - we should always
-     have it. */
-  if ((demux_res->num_time_to_samples==0) ||
-    (demux_res->num_sample_byte_sizes==0)) { return 0; }
-
-  /* Find the destination block from time_to_sample array */
-  i=0;
-  newblock=0;
-  newsample=0;
-  flag=0;
-
-  while ((i<demux_res->num_time_to_samples) && (flag==0) && 
-         (newsample < sample_loc)) {
-    j=(sample_loc-newsample) /
-      demux_res->time_to_sample[i].sample_duration;
+    uint32_t i;
+    uint32_t j;
+    uint32_t new_sample;
+    uint32_t new_sound_sample;
+    uint32_t new_pos;
+
+    /* First check we have the appropriate metadata - we should always
+     * have it.
+     */
+       
+    if ((demux_res->num_time_to_samples==0) ||
+       (demux_res->num_sample_byte_sizes==0))
+    { 
+        return 0; 
+    }
+
+    /* Find the destination block from time_to_sample array */
     
-    if (j <= demux_res->time_to_sample[i].sample_count) {
-      newblock+=j;
-      newsample+=j*demux_res->time_to_sample[i].sample_duration;
-      flag=1;
-    } else {
-      newsample+=(demux_res->time_to_sample[i].sample_duration
-                 * demux_res->time_to_sample[i].sample_count);
-      newblock+=demux_res->time_to_sample[i].sample_count;
-      i++;
+    i = 0;
+    new_sample = 0;
+    new_sound_sample = 0;
+
+    while ((i < demux_res->num_time_to_samples) &&
+        (new_sound_sample < sound_sample_loc)) 
+    {
+        j = (sound_sample_loc - new_sound_sample) /
+            demux_res->time_to_sample[i].sample_duration;
+    
+        if (j <= demux_res->time_to_sample[i].sample_count)
+        {
+            new_sample += j;
+            new_sound_sample += j * 
+                demux_res->time_to_sample[i].sample_duration;
+            break;
+        } 
+        else 
+        {
+            new_sound_sample += (demux_res->time_to_sample[i].sample_duration
+                * demux_res->time_to_sample[i].sample_count);
+            new_sample += demux_res->time_to_sample[i].sample_count;
+            i++;
+        }
     }
-  }
-
-  /* We know the new block, now calculate the file position */
-  newpos=demux_res->mdat_offset;
-  for (i=0;i<newblock;i++) {
-    newpos+=demux_res->sample_byte_size[i];
-  }
-
-  /* We know the new file position, so let's try to seek to it */
-  if (stream->ci->seek_buffer(newpos)) {
-    *samplesdone=newsample;
-    *currentblock=newblock;
-    return 1;
-  } else {
+
+    /* We know the new block, now calculate the file position. */
+  
+    new_pos = get_sample_offset(demux_res, new_sample);
+
+    /* We know the new file position, so let's try to seek to it */
+  
+    if (stream->ci->seek_buffer(new_pos)) 
+    {
+        *sound_samples_done = new_sound_sample;
+        *current_sample = new_sample;
+        return 1;
+    }
+    
     return 0;
-  }
 }
 
-/* Seek to file_loc (or close to it).  Return 1 on success (and
-   modify samplesdone and currentblock), 0 if failed 
-
-   Seeking uses the following array:
+/* Seek to the sample containing file_loc. Return 1 on success (and modify
+ * sound_samples_done and current_sample), 0 if failed.
+ *
+ * Seeking uses the following arrays:
+ *
+ * 1) the chunk_offset array contains the file offset of each chunk.
+ *
+ * 2) the sample_to_chunk array contains information about which chunk
+ *    of samples each sample belongs to.
+ *
+ * 3) the sample_byte_size array contains the length in bytes of each
+ *    sample.
+ *
+ * 4) the time_to_sample array contains the duration (in sound samples) 
+ *    of each sample of data.
+ *
+ * Locate the chunk containing location (using chunk_offset), find the 
+ * sample of that chunk (using sample_to_chunk) and finally the location
+ * of that sample (using sample_byte_size). Then use time_to_sample to
+ * calculate the sound_samples_done value.
+ */
+unsigned int alac_seek_raw(demux_res_t* demux_res, stream_t* stream,
+    uint32_t file_loc, uint32_t* sound_samples_done, 
+    int* current_sample)
+{
+    uint32_t chunk_sample = 0;
+    uint32_t total_samples = 0;
+    uint32_t new_sound_sample = 0;
+    uint32_t new_pos;
+    uint32_t chunk;
+    uint32_t i;
+
+    if (!demux_res->num_chunk_offsets ||
+        !demux_res->num_sample_to_chunks) 
+    {
+        return 0;
+    }
 
-     the sample_byte_size array contains the length in bytes of
-     each block ("sample" in Applespeak).
+    /* Locate the chunk containing file_loc. */
 
-   So we just find the last block before (or at) the requested position.
+    for (i = 0; i < demux_res->num_chunk_offsets && 
+        file_loc < demux_res->chunk_offset[i]; i++)
+    {
+    }
+    
+    chunk = i + 1;
+    new_pos = demux_res->chunk_offset[chunk - 1];
 
-   Each ALAC block seems to be independent of all the others.
- */
+    /* Get the first sample of the chunk. */
+    
+    for (i = 1; i < demux_res->num_sample_to_chunks &&
+        chunk < demux_res->sample_to_chunk[i - 1].first_chunk; i++) 
+    {
+        chunk_sample += demux_res->sample_to_chunk[i - 1].num_samples *
+            (demux_res->sample_to_chunk[i].first_chunk - 
+                demux_res->sample_to_chunk[i - 1].first_chunk);
+    }
+    
+    chunk_sample += (chunk - demux_res->sample_to_chunk[i - 1].first_chunk) *
+        demux_res->sample_to_chunk[i - 1].num_samples;
 
-unsigned int alac_seek_raw (demux_res_t* demux_res, 
-                        stream_t* stream,
-                        unsigned int file_loc, 
-                        uint32_t* samplesdone, int* currentblock)
-{
-  unsigned int i;
-  unsigned int j;
-  unsigned int newblock;
-  unsigned int newsample;
-  unsigned int newpos;
-
-  /* First check we have the appropriate metadata - we should always
-     have it. */
-  if ((demux_res->num_time_to_samples==0) ||
-    (demux_res->num_sample_byte_sizes==0)) { return 0; }
-
-  /* Find the destination block from the sample_byte_size array. */
-  newpos=demux_res->mdat_offset;
-  for (i=0;(i<demux_res->num_sample_byte_sizes) &&
-           (newpos+demux_res->sample_byte_size[i]<=file_loc);i++) {
-    newpos+=demux_res->sample_byte_size[i];
-  }
-  
-  newblock=i;
-  newsample=0;
-
-  /* Get the sample offset of the block */
-  for (i=0,j=0;(i<demux_res->num_time_to_samples) && (j<newblock);
-       i++,j+=demux_res->time_to_sample[i].sample_count) {
-    if (newblock-j < demux_res->time_to_sample[i].sample_count) {
-        newsample+=(newblock-j)*demux_res->time_to_sample[i].sample_duration;
-        break;
-    } else {
-        newsample+=(demux_res->time_to_sample[i].sample_duration
-                   * demux_res->time_to_sample[i].sample_count);
+    /* Get the position within the chunk. */
+    
+    for (; chunk_sample < demux_res->num_sample_byte_sizes; chunk_sample++)
+    {
+        if (file_loc < new_pos + demux_res->sample_byte_size[chunk_sample])
+        {
+            break;
+        }
+        
+        new_pos += demux_res->sample_byte_size[chunk_sample];
+    }
+    
+    /* Get sound sample offset. */
+
+    for (i = 0; i < demux_res->num_time_to_samples; i++)
+    {
+        if (chunk_sample < 
+            total_samples + demux_res->time_to_sample[i].sample_count)
+        {
+            break;
+        }
+        
+        total_samples += demux_res->time_to_sample[i].sample_count;
+        new_sound_sample += demux_res->time_to_sample[i].sample_count 
+            * demux_res->time_to_sample[i].sample_duration;
     }
-  }
+    
+    new_sound_sample += (chunk_sample - total_samples) 
+        * demux_res->time_to_sample[i].sample_duration;
+
+    /* Go to the new file position. */
+    
+    if (stream->ci->seek_buffer(new_pos)) 
+    {
+        *sound_samples_done = new_sound_sample;
+        *current_sample = chunk_sample;
+        return 1;
+    } 
 
-  /* We know the new file position, so let's try to seek to it */
-  if (stream->ci->seek_buffer(newpos)) {
-    *samplesdone=newsample;
-    *currentblock=newblock;
-    return 1;
-  } else {
     return 0;
-  }
 }
diff --git a/apps/codecs/libm4a/m4a.h b/apps/codecs/libm4a/m4a.h
index 7fea37513d..17f54c0146 100644
--- a/apps/codecs/libm4a/m4a.h
+++ b/apps/codecs/libm4a/m4a.h
@@ -33,12 +33,21 @@ typedef uint32_t fourcc_t;
 typedef struct
 {
     uint16_t num_channels;
-    uint16_t sample_size;
-    uint32_t sample_rate;
+    uint16_t sound_sample_size;
+    uint32_t sound_sample_rate;
     fourcc_t format;
     void *buf;
 
     struct {
+        uint32_t first_chunk;
+        uint32_t num_samples;
+    } *sample_to_chunk;
+    uint32_t num_sample_to_chunks;
+    
+    uint32_t *chunk_offset;
+    uint32_t num_chunk_offsets;
+    
+    struct {
         uint32_t sample_count;
         uint32_t sample_duration;
     } *time_to_sample;
@@ -93,16 +102,13 @@ void stream_skip(stream_t *stream, size_t skip);
 int stream_eof(stream_t *stream);
 
 void stream_create(stream_t *stream,struct codec_api* ci);
-int get_sample_info(demux_res_t *demux_res, uint32_t samplenum,
-                    uint32_t *sample_duration,
-                    uint32_t *sample_byte_size);
-unsigned int alac_seek (demux_res_t* demux_res,
-                        stream_t* stream,
-                        unsigned int sample_loc, 
-                        uint32_t* samplesdone, int* currentblock);
-unsigned int alac_seek_raw (demux_res_t* demux_res, 
-                        stream_t* stream,
-                        unsigned int file_loc, 
-                        uint32_t* samplesdone, int* currentblock);
+int get_sample_info(demux_res_t *demux_res, uint32_t sample,
+    uint32_t *sample_duration, uint32_t *sample_byte_size);
+unsigned int get_sample_offset(demux_res_t *demux_res, uint32_t sample);
+unsigned int alac_seek (demux_res_t* demux_res, stream_t* stream,
+    uint32_t sound_sample_loc, uint32_t* sound_samples_done, 
+    int* current_sample);
+unsigned int alac_seek_raw (demux_res_t* demux_res, stream_t* stream,
+    uint32_t file_loc, uint32_t* sound_samples_done, int* current_sample);
 
 #endif /* STREAM_H */