sub: do not clear subtitle list on seeking

This affects non-ASS text subtitles (those which go through libavcodec's
subtitle converter), which are muxed with video/audio. (Typically srt
subs in mkv.)

The problem is that seeking in the file can send a subtitle packet to
the decoder multiple times. These packets are interlaved with video,
and thus can't be all read when opening the file. Rather, subtitle
packets can essentially be randomly skipped or repeated (by seeking).
Until recently, this was solved by scanning the libass event list for
duplicates. Then our builtin srt-to-ass converter was removed, and
the problem was handled by fully clearing the subtitle list on each
seek.

This resulted in sub-seek not working properly for this type of file.
Since the subtitle list was cleared on seek, it was not possible to
do e.g. sub-seeks to subtitles before the current playback position.

Fix this by not clearing the list, and intead explicitly rejecting
duplicate packets. We use the packet file position was unique ID for
subtitles; this is confirmed working for most file formats (although
it is slightly risky - new demuxers may not necessarily set the file
position to something unique, or at all).

The list of seen packets is sorted, and the lookup uses binary search.
This is to avoid quadratic complexity when subtitles are added in
bulks, such as when opening a text subtitle file.

In some places, the code has to be adjusted to pass through the packet
file position correctly.

1 files changed, 1 insertions, 2 deletions

diff --git a/sub/sd.h b/sub/sd.h
index d2f22c5828..39b2970911 100644
--- a/sub/sd.h
+++ b/sub/sd.h
@@ -58,7 +58,6 @@ struct sd_functions {
     void (*uninit)(struct sd *sd);
 
     bool (*accepts_packet)(struct sd *sd); // implicit default if NULL: true
-    void (*fix_events)(struct sd *sd);
     int (*control)(struct sd *sd, enum sd_ctrl cmd, void *arg);
 
     // decoder
@@ -71,7 +70,7 @@ struct sd_functions {
 };
 
 void sd_conv_add_packet(struct sd *sd, void *data, int data_len, double pts,
-                        double duration);
+                        double duration, int64_t pos);
 struct demux_packet *sd_conv_def_get_converted(struct sd *sd);
 void sd_conv_def_reset(struct sd *sd);
 void sd_conv_def_uninit(struct sd *sd);