sub: use new FFmpeg API to check MicroDVD FPS

Before this, it wasn't possible to distinguish MicroDVD subtitles
without FPS header, and subtitles with FPS header equal to FFmpeg's
fallback FPS.

4 files changed, 21 insertions, 10 deletions

diff --git a/demux/demux_lavf.c b/demux/demux_lavf.c
index d85e4b8095..cc503383ea 100644
--- a/demux/demux_lavf.c
+++ b/demux/demux_lavf.c
@@ -461,11 +461,19 @@ static void handle_stream(demuxer_t *demuxer, int i)
         sh_sub->w = codec->width;
         sh_sub->h = codec->height;
 
-        // Hack for MicroDVD: if time_base matches the ffmpeg microdvd reader's
-        // default FPS (23.976), assume the MicroDVD file did not declare a
-        // FPS, and the MicroDVD file uses frame based timing.
-        if (codec->time_base.num == 125 && codec->time_base.den == 2997)
-            sh_sub->frame_based = true;
+        if (matches_avinputformat_name(priv, "microdvd")) {
+            AVRational r;
+            if (av_opt_get_q(avfc, "subfps", AV_OPT_SEARCH_CHILDREN, &r) >= 0) {
+                // File headers don't have a FPS set.
+                if (r.num < 1 || r.den < 1)
+                    sh_sub->frame_based = av_q2d(av_inv_q(codec->time_base));
+            } else {
+                // Older libavcodec versions. If the FPS matches the microdvd
+                // reader's default, assume it uses frame based timing.
+                if (codec->time_base.num == 125 && codec->time_base.den == 2997)
+                    sh_sub->frame_based = 23.976;
+            }
+        }
         break;
     }
     case AVMEDIA_TYPE_ATTACHMENT: {
diff --git a/demux/demux_subreader.c b/demux/demux_subreader.c
index 1fa449d7f0..d72cc209c9 100644
--- a/demux/demux_subreader.c
+++ b/demux/demux_subreader.c
@@ -1361,7 +1361,7 @@ static int d_open_file(struct demuxer *demuxer, enum demux_check check)
 
     p->sh = new_sh_stream(demuxer, STREAM_SUB);
     p->sh->codec = sd->codec;
-    p->sh->sub->frame_based = !sd->sub_uses_time;
+    p->sh->sub->frame_based = sd->sub_uses_time ? 0 : 23.976;
     p->sh->sub->is_utf8 = sr.args.utf16 != 0; // converted from utf-16 -> utf-8
 
     add_sub_data(demuxer, sd);
diff --git a/demux/stheader.h b/demux/stheader.h
index 177bf50b39..573d6ac3c6 100644
--- a/demux/stheader.h
+++ b/demux/stheader.h
@@ -88,7 +88,8 @@ typedef struct sh_sub {
     unsigned char *extradata;   // extra header data passed from demuxer
     int extradata_len;
     int w, h;                   // mp4 vobsubs
-    int frame_based;            // timestamps are frame-based
+    double frame_based;         // timestamps are frame-based (and this is the
+                                // fallback framerate used for timestamps)
     bool is_utf8;               // if false, subtitle packet charset is unknown
     struct ass_track *track;    // loaded by libass
     struct dec_sub *dec_sub;    // decoder context
diff --git a/sub/dec_sub.c b/sub/dec_sub.c
index fdb8d8f648..0a62e52a15 100644
--- a/sub/dec_sub.c
+++ b/sub/dec_sub.c
@@ -464,9 +464,11 @@ bool sub_read_all_packets(struct dec_sub *sub, struct sh_stream *sh)
 
     double sub_speed = 1.0;
 
-    // 23.976 FPS is used as default timebase for frame based formats
-    if (sub->video_fps && sh->sub->frame_based)
-        sub_speed *= 23.976 / sub->video_fps;
+    if (sub->video_fps && sh->sub->frame_based > 0) {
+        MP_VERBOSE(sub, "Frame based format, dummy FPS: %f, video FPS: %f\n",
+                   sh->sub->frame_based, sub->video_fps);
+        sub_speed *= sh->sub->frame_based / sub->video_fps;
+    }
 
     if (opts->sub_fps && sub->video_fps)
         sub_speed *= opts->sub_fps / sub->video_fps;