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 ...
Attached is a patch to dvdnav_sector_search which guarantees that an
attempted forward seek always moves the current position forward.
diff -Naur libdvdnav.orig/src/searching.c libdvdnav/src/searching.c
--- libdvdnav.orig/src/searching.c 2009-01-08 14:57:11.000000000 -0800
+++ libdvdnav/src/searching.c 2009-09-12 13:47:33.880551499 -0700
@@ -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, uint8_t next, uint32_t *vobu) {
vobu_admap_t *admap = NULL;
#ifdef LOG_DEBUG
@@ -89,7 +89,10 @@
vobu_start = next_vobu;
address++;
}
- *vobu = vobu_start;
+ if(next)
+ *vobu = next_vobu;
+ else
+ *vobu = vobu_start;
return DVDNAV_STATUS_OK;
}
fprintf(MSG_OUT, "libdvdnav: admap not located\n");
@@ -160,7 +163,7 @@
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 +187,11 @@
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 length = 0;
uint32_t first_cell_nr, last_cell_nr, cell_nr;
int32_t found;
+ int32_t forward = 0;
cell_playback_t *cell;
dvd_state_t *state;
dvdnav_status_t result;
@@ -200,6 +205,7 @@
if(!result) {
return DVDNAV_STATUS_ERR;
}
+ current_pos = target;
pthread_mutex_lock(&this->vm_lock);
state = &(this->vm->state);
@@ -244,6 +250,8 @@
pthread_mutex_unlock(&this->vm_lock);
return DVDNAV_STATUS_ERR;
}
+ if (target > current_pos)
+ forward = 1;
this->cur_cell_time = 0;
if (this->pgc_based) {
@@ -270,6 +278,33 @@
} else {
/* convert the target sector from Cell-relative to absolute physical
sector */
target += cell->first_sector;
+ if (forward) {
+ 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) {
+ if (vobu <= current_pos) {
+ if (dvdnav_scan_admap(this, state->domain, target, 1, &vobu) ==
DVDNAV_STATUS_OK) {
+ if (vobu > cell->last_sector) {
+ if (cell_nr == last_cell_nr) {
+ break;
+ } else {
+ cell_nr++;
+ cell = &(state->pgc->cell_playback[cell_nr-1]);
+ target = cell->first_sector;
+ }
+ } else {
+ target = vobu;
+ }
+ } else {
+ break;
+ }
+ }
+ } else {
+ break;
+ }
+ }
found = 1;
break;
}
@@ -281,7 +316,7 @@
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)) {
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