A new and hopefully clearer explanation of how to apply PTS values in streams from DVDs.

The liba52 sync code should be made to create the correct output A52 frames with correct PTS values attached.

CVS patchset: 5756
CVS date: 2003/11/16 22:20:08

1 files changed, 93 insertions, 3 deletions

diff --git a/src/demuxers/demux_mpeg_block.c b/src/demuxers/demux_mpeg_block.c
index b9428bf72..dd8342312 100644
--- a/src/demuxers/demux_mpeg_block.c
+++ b/src/demuxers/demux_mpeg_block.c
@@ -17,7 +17,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA
  *
- * $Id: demux_mpeg_block.c,v 1.199 2003/11/16 15:31:51 mroi Exp $
+ * $Id: demux_mpeg_block.c,v 1.200 2003/11/16 22:20:08 jcdutton Exp $
  *
  * demultiplexer for mpeg 1/2 program streams
  * used with fixed blocksize devices (like dvd/vcd)
@@ -769,8 +769,98 @@ static int32_t parse_private_stream_1(demux_mpeg_block_t *this, uint8_t *p, buf_
     if ((p[0]&0xF0) == 0x80) {
     
       track = p[0] & 0x0F; /* hack : ac3 track */
-      buf->decoder_info[1] = p[1]; /* Number of frame headers */
-      buf->decoder_info[2] = p[2] << 8 | p[3]; /* First access unit pointer */
+
+      /* Number of frame headers 
+       *
+       * Describes the number of a52 frame headers that start in this pack (One pack per DVD sector).
+       *
+       * Likely values: 1 or 2.
+       */
+      buf->decoder_info[1] = p[1];
+      /* First access unit pointer. 
+       *
+       * Describes the byte offset within this pack to the beginning of the first A52 frame header.
+       * The PTS from this pack applies to the beginning of the first A52 frame that starts in this pack.
+       * Any bytes before this offset should be considered to belong to the previous A52 frame. 
+       * and therefore be tagged with a PTS value derived from the previous pack.
+       *
+       * Likely values: Anything from 1 to the size of an A52 frame.
+       */
+      buf->decoder_info[2] = p[2] << 8 | p[3];
+      /* Summary: If the first pack contains the beginning of 2 A52 frames( decoder_info[1]=2),
+       *            the PTS value applies to the first A52 frame.
+       *          The second A52 frame will have no PTS value.
+       *          The start of the next pack will contain the rest of the second A52 frame and thus, no PTS value.
+       *          The third A52 frame will have the PTS value from the second pack.
+       *
+       *          If the first pack contains the beginning of 1 frame( decoder_info[1]=1 ),
+       *            this first pack must then contain a certain amount of the previous A52 frame.
+       *            the PTS value will not apply to this previous A52 frame,
+       *            the PTS value will apply to the beginning of the frame that begins in this pack.
+       *
+       * LPCM note: The first_access_unit_pointer will point to
+       *            the PCM sample within the pack at which the PTS values applies.
+       *
+       * Example to values in a real stream, each line is a pack (dvd sector): -
+       * decoder_info[1], decoder_info[2],  PTS
+       * 2                   5             125640
+       * 1                1061             131400
+       * 1                 581             134280
+       * 2                 101             137160
+       * 1                1157             142920
+       * 1                 677             145800
+       * 2                 197             148680
+       * 1                1253             154440
+       * 1                 773             157320
+       * 2                 293             160200
+       * 1                1349             165960
+       * 1                 869             168840
+       * 2                 389             171720
+       * 1                1445             177480
+       * 1                 965             180360
+       * 1                 485             183240
+       * 2                   5             186120
+       * 1                1061             191880
+       * 1                 581             194760
+       * 2                 101             197640
+       * 1                1157             203400
+       * 1                 677             206280
+       * 2                 197             209160
+       * Notice the repeating pattern of both decoder_info[1] and decoder_info[2].
+       * The resulting A52 frames will have these PTS values: -
+       *  PTS
+       * 125640
+       *      0
+       * 131400
+       * 134280
+       * 137160
+       *      0
+       * 142920
+       * 145800
+       * 148680
+       *      0
+       * 154440
+       * 157320
+       * 160200
+       *      0
+       * 165960
+       * 168840
+       * 171720
+       *      0
+       * 177480
+       * 180360
+       * 183240
+       * 186120
+       *      0
+       * 191880
+       * 194760
+       * 197640
+       *      0
+       * 203400
+       * 206280
+       * 209160
+       *      0 (Partial A52 frame.)
+       */
 
       buf->content   = p+4;
       buf->size      = this->packet_len-4;