[DVDnav-discuss] r1239 - trunk/libdvdnav/src/searching.c

[erik]

Author: erik
Date: Fri Oct  7 19:06:24 2011
New Revision: 1239

Log:
Always attempt to move forward on a seek

>From John Stebbins original post (with pathc, Thanks!):
libdvdnav has a problem in that it is difficult to gracefully recover
from a read error and continue on to subsequent blocks on the disc.  An
application would like to seek forward past the current block after
getting a read error in order to attempt to get past the bad block(s).
But dvdnav_sector_search() does not guarantee that a requested forward
seek will actually move the current position forward.  It truncates down
to the nearest VOBU which will almost always cause a forward seek
request by a single block (or a small number of blocks) to move the
current position backward.  This behaviour puts the application into a
loop of: read failure, attempted forward seek (which results in backward
seek), read failure ...

Modified:
   trunk/libdvdnav/src/searching.c

Modified: trunk/libdvdnav/src/searching.c
==============================================================================
--- trunk/libdvdnav/src/searching.c	Fri Oct  7 18:56:02 2011	(r1238)
+++ trunk/libdvdnav/src/searching.c	Fri Oct  7 19:06:24 2011	(r1239)
@@ -47,7 +47,7 @@
 /* Return placed in vobu. */
 /* Returns error status */
 /* FIXME: Maybe need to handle seeking outside current cell. */
-static dvdnav_status_t dvdnav_scan_admap(dvdnav_t *this, int32_t domain, uint32_t seekto_block, uint32_t *vobu) {
+static dvdnav_status_t dvdnav_scan_admap(dvdnav_t *this, int32_t domain, uint32_t seekto_block, int next, uint32_t *vobu) {
   vobu_admap_t *admap = NULL;
 
 #ifdef LOG_DEBUG
@@ -89,7 +89,7 @@ static dvdnav_status_t dvdnav_scan_admap
       vobu_start = next_vobu;
       address++;
     }
-    *vobu = vobu_start;
+    *vobu = next ? next_vobu : vobu_start;
     return DVDNAV_STATUS_OK;
   }
   fprintf(MSG_OUT, "libdvdnav: admap not located\n");
@@ -160,7 +160,7 @@ dvdnav_status_t dvdnav_time_search(dvdna
     fprintf(MSG_OUT, "libdvdnav: Seeking to cell %i from choice of %i to %i\n",
 	    cell_nr, first_cell_nr, last_cell_nr);
 #endif
-    if (dvdnav_scan_admap(this, state->domain, target, &vobu) == DVDNAV_STATUS_OK) {
+    if (dvdnav_scan_admap(this, state->domain, target, 0, &vobu) == DVDNAV_STATUS_OK) {
       uint32_t start = state->pgc->cell_playback[cell_nr-1].first_sector;
 
       if (vm_jump_cell_block(this->vm, cell_nr, vobu - start)) {
@@ -184,9 +184,13 @@ dvdnav_status_t dvdnav_time_search(dvdna
 dvdnav_status_t dvdnav_sector_search(dvdnav_t *this,
 				     uint64_t offset, int32_t origin) {
   uint32_t target = 0;
+  uint32_t current_pos;
+  uint32_t cur_sector;
+  uint32_t cur_cell_nr;
   uint32_t length = 0;
   uint32_t first_cell_nr, last_cell_nr, cell_nr;
   int32_t found;
+  int forward = 0;
   cell_playback_t *cell;
   dvd_state_t *state;
   dvdnav_status_t result;
@@ -213,6 +217,10 @@ dvdnav_status_t dvdnav_sector_search(dvd
   fprintf(MSG_OUT, "libdvdnav: Before cellN=%u blockN=%u\n", state->cellN, state->blockN);
 #endif
 
+  current_pos = target;
+  cur_sector = this->vobu.vobu_start + this->vobu.blockN;
+  cur_cell_nr = state->cellN;
+
   switch(origin) {
    case SEEK_SET:
     if(offset >= length) {
@@ -244,6 +252,7 @@ dvdnav_status_t dvdnav_sector_search(dvd
     pthread_mutex_unlock(&this->vm_lock);
     return DVDNAV_STATUS_ERR;
   }
+  forward = target > current_pos;
 
   this->cur_cell_time = 0;
   if (this->pgc_based) {
@@ -270,6 +279,27 @@ dvdnav_status_t dvdnav_sector_search(dvd
     } else {
       /* convert the target sector from Cell-relative to absolute physical sector */
       target += cell->first_sector;
+      if (forward && (cell_nr == cur_cell_nr)) {
+        uint32_t vobu;
+        /* if we are seeking forward from the current position, make sure
+         * we move to a new position that is after our current position.
+         * simply truncating to the vobu will go backwards */
+        if (dvdnav_scan_admap(this, state->domain, target, 0, &vobu) != DVDNAV_STATUS_OK)
+          break;
+        if (vobu <= cur_sector) {
+          if (dvdnav_scan_admap(this, state->domain, target, 1, &vobu) != DVDNAV_STATUS_OK)
+            break;
+          if (vobu > cell->last_sector) {
+            if (cell_nr == last_cell_nr)
+              break;
+            cell_nr++;
+            cell =  &(state->pgc->cell_playback[cell_nr-1]);
+            target = cell->first_sector;
+          } else {
+            target = vobu;
+          }
+        }
+      }
       found = 1;
       break;
     }
@@ -281,7 +311,7 @@ dvdnav_status_t dvdnav_sector_search(dvd
     fprintf(MSG_OUT, "libdvdnav: Seeking to cell %i from choice of %i to %i\n",
 	    cell_nr, first_cell_nr, last_cell_nr);
 #endif
-    if (dvdnav_scan_admap(this, state->domain, target, &vobu) == DVDNAV_STATUS_OK) {
+    if (dvdnav_scan_admap(this, state->domain, target, 0, &vobu) == DVDNAV_STATUS_OK) {
       int32_t start = state->pgc->cell_playback[cell_nr-1].first_sector;
 
       if (vm_jump_cell_block(this->vm, cell_nr, vobu - start)) {