Allows shifting of subtitle display times to align them with the video.
This avoids having to rewrite the subtitle file in order to display
subtitles correctly when input is seeked (-ss).
Also handy for minor subtitle timing corrections without rewriting the
subtitles file.
Signed-off-by: Manolis Stamatogiannakis <msta...@gmail.com>
---
doc/filters.texi | 8 ++++++++
libavfilter/vf_subtitles.c | 29 +++++++++++++++++++++++++++--
2 files changed, 35 insertions(+), 2 deletions(-)
diff --git a/doc/filters.texi b/doc/filters.texi
index d19fd346ae..94323495f0 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -17851,6 +17851,9 @@ The filter accepts the following options:
@item filename, f
Set the filename of the subtitle file to read. It must be specified.
+@item shift
+Shift subtitles timings by the specified amount.
+
@item original_size
Specify the size of the original video, the video for which the ASS file
was composed. For the syntax of this option, check the
@@ -17907,6 +17910,11 @@ To make the subtitles stream from @file{sub.srt}
appear in 80% transparent blue
subtitles=sub.srt:force_style='FontName=DejaVu Serif,PrimaryColour=&HCCFF0000'
@end example
+To re-sync subtitles after seeking the input e.g. with @code{-ss 20:20}, use:
+@example
+subtitles=filename=sub.srt:shift=-20\:20
+@end example
+
@section super2xsai
Scale the input by 2x and smooth using the Super2xSaI (Scale and
diff --git a/libavfilter/vf_subtitles.c b/libavfilter/vf_subtitles.c
index a3b4029af4..74a902941a 100644
--- a/libavfilter/vf_subtitles.c
+++ b/libavfilter/vf_subtitles.c
@@ -52,6 +52,8 @@ typedef struct AssContext {
char *filename;
char *fontsdir;
char *charenc;
+ int64_t shift;
+ char *shift_opt;
char *force_style;
int stream_index;
int alpha;
@@ -68,6 +70,7 @@ typedef struct AssContext {
#define COMMON_OPTIONS \
{"filename", "set the filename of file to read",
OFFSET(filename), AV_OPT_TYPE_STRING, {.str = NULL}, 0, 0, FLAGS }, \
{"f", "set the filename of file to read",
OFFSET(filename), AV_OPT_TYPE_STRING, {.str = NULL}, 0, 0, FLAGS }, \
+ {"shift", "set the tilename of file to read",
OFFSET(shift_opt), AV_OPT_TYPE_STRING, {.str = NULL}, 0, 0, FLAGS }, \
{"original_size", "set the size of the original video (used to scale
fonts)", OFFSET(original_w), AV_OPT_TYPE_IMAGE_SIZE, {.str = NULL}, 0, 0,
FLAGS }, \
{"fontsdir", "set the directory containing the fonts to read",
OFFSET(fontsdir), AV_OPT_TYPE_STRING, {.str = NULL}, 0, 0, FLAGS }, \
{"alpha", "enable processing of alpha channel",
OFFSET(alpha), AV_OPT_TYPE_BOOL, {.i64 = 0 }, 0,
1, FLAGS }, \
@@ -103,6 +106,16 @@ static av_cold int init(AVFilterContext *ctx)
return AVERROR(EINVAL);
}
+ if (ass->shift_opt) {
+ if (av_parse_time(&ass->shift, ass->shift_opt, 1) < 0) {
+ av_log(ctx, AV_LOG_ERROR, "Invalid subtitles shift: %s\n",
+ ass->shift_opt);
+ return AVERROR(EINVAL);
+ }
+ ass->shift = av_rescale_q(ass->shift, AV_TIME_BASE_Q, av_make_q(1,
1000));
+ av_log(ctx, AV_LOG_DEBUG, "Shifting subtitles by %0.3fsec.\n",
ass->shift/1000.0);
+ }
+
ass->library = ass_library_init();
if (!ass->library) {
av_log(ctx, AV_LOG_ERROR, "Could not initialize libass.\n");
@@ -297,7 +310,7 @@ AVFILTER_DEFINE_CLASS(subtitles);
static av_cold int init_subtitles(AVFilterContext *ctx)
{
- int j, ret, sid;
+ int j, ret, sid, nskip;
int k = 0;
AVDictionary *codec_opts = NULL;
AVFormatContext *fmt = NULL;
@@ -448,6 +461,7 @@ static av_cold int init_subtitles(AVFilterContext *ctx)
av_init_packet(&pkt);
pkt.data = NULL;
pkt.size = 0;
+ nskip = 0;
while (av_read_frame(fmt, &pkt) >= 0) {
int i, got_subtitle;
AVSubtitle sub = {0};
@@ -458,8 +472,17 @@ static av_cold int init_subtitles(AVFilterContext *ctx)
av_log(ctx, AV_LOG_WARNING, "Error decoding: %s (ignored)\n",
av_err2str(ret));
} else if (got_subtitle) {
- const int64_t start_time = av_rescale_q(sub.pts,
AV_TIME_BASE_Q, av_make_q(1, 1000));
+ const int64_t start_time = av_rescale_q(sub.pts,
AV_TIME_BASE_Q, av_make_q(1, 1000)) + ass->shift;
const int64_t duration = sub.end_display_time;
+
+ if (start_time + duration < 0) {
+ nskip++;
+ goto pkt_end;
+ } else if (nskip > 0) {
+ av_log(ctx, AV_LOG_INFO, "Skipped %d subtitles out of time
range.\n", nskip);
+ nskip = 0;
+ }
+
for (i = 0; i < sub.num_rects; i++) {
char *ass_line = sub.rects[i]->ass;
if (!ass_line)
@@ -472,6 +495,8 @@ static av_cold int init_subtitles(AVFilterContext *ctx)
}
}
}
+
+pkt_end:
av_packet_unref(&pkt);
avsubtitle_free(&sub);
}
--
2.17.1
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