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sd_ass: disable special handling of subtitles with duration 0

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sd_ass contains some code that treats subtitle events with duration 0
specially, and adjust their duration so that they will disappear with
the next event.

This is most likely not needed anymore. Some subtitle formats allow
omitting the duration so that the event is visible until the next one,
but both subreader.c as well as libavformat subtitle demuxers already
handle this.

Subtitles embedded in mp4 files (movtext) used to trigger this code. But
these files appear to export subtitle duration correctly (at least
libavcodec's movtext decoder is using this assumption). Since commit
6dbedd2 changed demux_lavf to actually copy the packet duration field,
the code removed with this commit isn't needed anymore for correct
display of movtext subtitles. (The change in sd_movtext is for dropping
empty subtitle events, which would now be "displayed" - libavcodec does
the same.)

On the other hand, this code incorrectly displayed hidden events in .srt
subtitles. See for example the first event in SubRip_capability_tester.srt
(part of FFmpeg's FATE). These intentionally have a duration of 0, and
should not be displayed. (As of with this commit, they are still
displayed in external .srt subs because of subreader.c hacks.)

However, we can't be 100% sure that this code is really unneeded, so
just comment the code. Hopefully it can be removed if there are no
regressions after some weeks or months.
This commit is contained in:
wm4 2013-06-23 22:10:10 +02:00
parent 1058d80a5e
commit 7e033da892
2 changed files with 22 additions and 1 deletions
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20
sub/sd_ass.c
View File

@ -32,6 +32,10 @@
#include "ass_mp.h"
#include "sd.h"
// Enable code that treats subtitle events with duration 0 specially, and
// adjust their duration so that they will disappear with the next event.
#define INCOMPLETE_EVENTS 0
struct sd_ass_priv {
struct ass_track *ass_track;
bool vsfilter_aspect;
@ -114,6 +118,7 @@ static void decode(struct sd *sd, struct demux_packet *packet)
}
long long ipts = pts * 1000 + 0.5;
long long iduration = duration * 1000 + 0.5;
#if INCOMPLETE_EVENTS
if (ctx->incomplete_event) {
ctx->incomplete_event = false;
ASS_Event *event = track->events + track->n_events - 1;
@ -144,6 +149,21 @@ static void decode(struct sd *sd, struct demux_packet *packet)
iduration = 10000;
ctx->incomplete_event = true;
}
#else
if (duration <= 0) {
mp_msg(MSGT_SUBREADER, MSGL_WARN, "Subtitle without duration or "
"duration set to 0 at pts %f, ignored\n", pts);
return;
}
if (!sd->no_remove_duplicates) {
for (int i = 0; i < track->n_events; i++) {
if (track->events[i].Start == ipts
&& (track->events[i].Duration == iduration)
&& strcmp(track->events[i].Text, text) == 0)
return; // We've already added this subtitle
}
}
#endif
int eid = ass_alloc_event(track);
ASS_Event *event = track->events + eid;
event->Start = ipts;

3
sub/sd_movtext.c
View File

@ -42,7 +42,8 @@ static void decode(struct sd *sd, struct demux_packet *packet)
return;
len = FFMIN(len - 2, AV_RB16(data));
data += 2;
sd_conv_add_packet(sd, data, len, packet->pts, packet->duration);
if (len > 0)
sd_conv_add_packet(sd, data, len, packet->pts, packet->duration);
}
const struct sd_functions sd_movtext = {