[FFmpeg-devel] [PATCH] ffmpeg: explicitly handle sub2video subpicture initialization

[Jan Ekström]

Each time the sub2video structure is initialized, the sub2video
subpicture is initialized together with the first received heartbeat.
The heartbeat's PTS is utilized as the subpicture start time.

Additionally, add some documentation on the stages.
---
 fftools/ffmpeg.c        | 22 +++++++++++++++-------
 fftools/ffmpeg.h        |  3 ++-
 fftools/ffmpeg_filter.c |  8 +++++++-
 3 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
index 544f1a1cef..efe903cc41 100644
--- a/fftools/ffmpeg.c
+++ b/fftools/ffmpeg.c
@@ -237,7 +237,7 @@ static void sub2video_push_ref(InputStream *ist, int64_t pts)
     }
 }
 
-void sub2video_update(InputStream *ist, AVSubtitle *sub)
+void sub2video_update(InputStream *ist, int64_t heartbeat_pts, AVSubtitle *sub)
 {
     AVFrame *frame = ist->sub2video.frame;
     int8_t *dst;
@@ -254,7 +254,12 @@ void sub2video_update(InputStream *ist, AVSubtitle *sub)
                                  AV_TIME_BASE_Q, ist->st->time_base);
         num_rects = sub->num_rects;
     } else {
-        pts       = ist->sub2video.end_pts;
+        /* If we are initializing the system, utilize current heartbeat
+           PTS as the start time, and show until the following subpicture
+           is received. Otherwise, utilize the previous subpicture's end time
+           as the fall-back value. */
+        pts       = ist->sub2video.initialize ?
+                    heartbeat_pts : ist->sub2video.end_pts;
         end_pts   = INT64_MAX;
         num_rects = 0;
     }
@@ -269,6 +274,7 @@ void sub2video_update(InputStream *ist, AVSubtitle *sub)
         sub2video_copy_rect(dst, dst_linesize, frame->width, frame->height, sub->rects[i]);
     sub2video_push_ref(ist, pts);
     ist->sub2video.end_pts = end_pts;
+    ist->sub2video.initialize = 0;
 }
 
 static void sub2video_heartbeat(InputStream *ist, int64_t pts)
@@ -291,9 +297,11 @@ static void sub2video_heartbeat(InputStream *ist, int64_t pts)
         /* do not send the heartbeat frame if the subtitle is already ahead */
         if (pts2 <= ist2->sub2video.last_pts)
             continue;
-        if (pts2 >= ist2->sub2video.end_pts ||
-            (!ist2->sub2video.frame->data[0] && ist2->sub2video.end_pts < INT64_MAX))
-            sub2video_update(ist2, NULL);
+        if (pts2 >= ist2->sub2video.end_pts || ist2->sub2video.initialize)
+            /* if we have hit the end of the current displayed subpicture,
+               or if we need to initialize the system, update the
+               overlayed subpicture and its start/end times */
+            sub2video_update(ist2, pts2 + 1, NULL);
         for (j = 0, nb_reqs = 0; j < ist2->nb_filters; j++)
             nb_reqs += av_buffersrc_get_nb_failed_requests(ist2->filters[j]->filter);
         if (nb_reqs)
@@ -307,7 +315,7 @@ static void sub2video_flush(InputStream *ist)
     int ret;
 
     if (ist->sub2video.end_pts < INT64_MAX)
-        sub2video_update(ist, NULL);
+        sub2video_update(ist, INT64_MAX, NULL);
     for (i = 0; i < ist->nb_filters; i++) {
         ret = av_buffersrc_add_frame(ist->filters[i]->filter, NULL);
         if (ret != AVERROR_EOF && ret < 0)
@@ -2514,7 +2522,7 @@ static int transcode_subtitles(InputStream *ist, AVPacket *pkt, int *got_output,
         return ret;
 
     if (ist->sub2video.frame) {
-        sub2video_update(ist, &subtitle);
+        sub2video_update(ist, INT64_MIN, &subtitle);
     } else if (ist->nb_filters) {
         if (!ist->sub2video.sub_queue)
             ist->sub2video.sub_queue = av_fifo_alloc(8 * sizeof(AVSubtitle));
diff --git a/fftools/ffmpeg.h b/fftools/ffmpeg.h
index eb1eaf6363..b2129a3f28 100644
--- a/fftools/ffmpeg.h
+++ b/fftools/ffmpeg.h
@@ -349,6 +349,7 @@ typedef struct InputStream {
         AVFifoBuffer *sub_queue;    ///< queue of AVSubtitle* before filter init
         AVFrame *frame;
         int w, h;
+        unsigned int initialize; ///< marks if sub2video_update should force an initialization
     } sub2video;
 
     int dr1;
@@ -646,7 +647,7 @@ int filtergraph_is_simple(FilterGraph *fg);
 int init_simple_filtergraph(InputStream *ist, OutputStream *ost);
 int init_complex_filtergraph(FilterGraph *fg);
 
-void sub2video_update(InputStream *ist, AVSubtitle *sub);
+void sub2video_update(InputStream *ist, int64_t heartbeat_pts, AVSubtitle *sub);
 
 int ifilter_parameters_from_frame(InputFilter *ifilter, const AVFrame *frame);
 
diff --git a/fftools/ffmpeg_filter.c b/fftools/ffmpeg_filter.c
index 72838de1e2..d81bb9742f 100644
--- a/fftools/ffmpeg_filter.c
+++ b/fftools/ffmpeg_filter.c
@@ -740,6 +740,12 @@ static int sub2video_prepare(InputStream *ist, InputFilter *ifilter)
         return AVERROR(ENOMEM);
     ist->sub2video.last_pts = INT64_MIN;
     ist->sub2video.end_pts  = INT64_MIN;
+
+    /* sub2video structure has been (re-)initialized.
+       Mark it as such so that the system will be
+       initialized with the first received heartbeat. */
+    ist->sub2video.initialize = 1;
+
     return 0;
 }
 
@@ -1169,7 +1175,7 @@ int configure_filtergraph(FilterGraph *fg)
             while (av_fifo_size(ist->sub2video.sub_queue)) {
                 AVSubtitle tmp;
                 av_fifo_generic_read(ist->sub2video.sub_queue, &tmp, sizeof(tmp), NULL);
-                sub2video_update(ist, &tmp);
+                sub2video_update(ist, INT64_MIN, &tmp);
                 avsubtitle_free(&tmp);
             }
         }
-- 
2.20.1