[FFmpeg-devel] subtitle filter

[Iliya Bunov]

It is impossible to make a screenshot with hardsubs.
ffmpeg -ss 00:10:57 -t 1 -i m.mkv -vf "ass=m.ass" -f mjpeg image01.png
Subtitles always start from the beginning (00:00 not 00:10:57).

Adding "ss" option can solve this problem.
ffmpeg -ss 00:10:57 -t 1 -i m.mkv -vf "ass=m.ass:ss='10\:57'" -f mjpeg
image01.png

PATCH

diff --git a/libavfilter/vf_subtitles.c b/libavfilter/vf_subtitles.c
index e44f61d..c742155 100644
--- a/libavfilter/vf_subtitles.c
+++ b/libavfilter/vf_subtitles.c
@@ -54,6 +54,7 @@ typedef struct {
     uint8_t rgba_map[4];
     int     pix_step[4];       ///< steps per pixel for each plane of the
main output
     int original_w, original_h;
+    int64_t ss;
     FFDrawContext draw;
 } AssContext;

@@ -64,6 +65,7 @@ typedef struct {
     {"filename",       "set the filename of file to read",
        OFFSET(filename),   AV_OPT_TYPE_STRING,     {.str = NULL},
 CHAR_MIN, CHAR_MAX, FLAGS }, \
     {"f",              "set the filename of file to read",
        OFFSET(filename),   AV_OPT_TYPE_STRING,     {.str = NULL},
 CHAR_MIN, CHAR_MAX, FLAGS }, \
     {"original_size",  "set the size of the original video (used to scale
fonts)", OFFSET(original_w), AV_OPT_TYPE_IMAGE_SIZE, {.str = NULL},
 CHAR_MIN, CHAR_MAX, FLAGS }, \
+    {"ss",             "set subtitle time offset",
        OFFSET(ss),         AV_OPT_TYPE_DURATION,   {.i64 = 0.},
0, INT32_MAX, FLAGS }, \

 /* libass supports a log level ranging from 0 to 7 */
 static const int ass_libavfilter_log_level_map[] = {
@@ -170,7 +172,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame
*picref)
     AVFilterLink *outlink = ctx->outputs[0];
     AssContext *ass = ctx->priv;
     int detect_change = 0;
-    double time_ms = picref->pts * av_q2d(inlink->time_base) * 1000;
+    double time_ms = picref->pts * av_q2d(inlink->time_base) * 1000 +
ass->ss / 1000;
     ASS_Image *image = ass_render_frame(ass->renderer, ass->track,
                                         time_ms, &detect_change);