[FFmpeg-devel] [RFC PATCH 2/5] vf_fps: properly preserve CEA-708 captions

[Devin Heitmueller <devin.heitmueller@ltnglobal.com>]

The existing implementation made an attempt to remove duplicate
captions if increasing the framerate, but made no attempt to
handle reducing the framerate, nor did it rewrite the caption
payloads to have the appropriate cc_count (e.g. the cc_count needs
to change from 20 to 10 when going from 1080i59 to 720p59 and
vice-versa).

Make use of the new ccfifo mechanism to ensure that caption data
is properly preserved.

Signed-off-by: Devin Heitmueller <dheitmueller@ltnglobal.com>
---
 libavfilter/vf_fps.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/libavfilter/vf_fps.c b/libavfilter/vf_fps.c
index 051d278f54..d2fab09c66 100644
--- a/libavfilter/vf_fps.c
+++ b/libavfilter/vf_fps.c
@@ -30,6 +30,7 @@
 #include <stdint.h>
 
 #include "libavutil/avassert.h"
+#include "libavutil/ccfifo.h"
 #include "libavutil/eval.h"
 #include "libavutil/mathematics.h"
 #include "libavutil/opt.h"
@@ -85,6 +86,7 @@ typedef struct FPSContext {
 
     AVFrame *frames[2];     ///< buffered frames
     int      frames_count;  ///< number of buffered frames
+    AVCCFifo *cc_fifo;      ///< closed captions
 
     int64_t  next_pts;      ///< pts of the next frame to output
 
@@ -165,6 +167,7 @@ static av_cold void uninit(AVFilterContext *ctx)
         frame = shift_frame(ctx, s);
         av_frame_free(&frame);
     }
+    av_ccfifo_freep(&s->cc_fifo);
 
     av_log(ctx, AV_LOG_VERBOSE, "%d frames in, %d frames out; %d frames dropped, "
            "%d frames duplicated.\n", s->frames_in, s->frames_out, s->drop, s->dup);
@@ -210,6 +213,9 @@ static int config_props(AVFilterLink* outlink)
                s->in_pts_off, s->out_pts_off, s->start_time);
     }
 
+    if (!(s->cc_fifo = av_ccfifo_alloc(&outlink->frame_rate, ctx)))
+        av_log(ctx, AV_LOG_VERBOSE, "Failure to setup CC FIFO queue.  Captions will be passed through\n");
+
     av_log(ctx, AV_LOG_VERBOSE, "fps=%d/%d\n", outlink->frame_rate.num, outlink->frame_rate.den);
 
     return 0;
@@ -242,6 +248,7 @@ static int read_frame(AVFilterContext *ctx, FPSContext *s, AVFilterLink *inlink,
     av_log(ctx, AV_LOG_DEBUG, "Read frame with in pts %"PRId64", out pts %"PRId64"\n",
            in_pts, frame->pts);
 
+    av_ccfifo_extract(s->cc_fifo, frame);
     s->frames[s->frames_count++] = frame;
     s->frames_in++;
 
@@ -289,7 +296,7 @@ static int write_frame(AVFilterContext *ctx, FPSContext *s, AVFilterLink *outlin
         if (!frame)
             return AVERROR(ENOMEM);
         // Make sure Closed Captions will not be duplicated
-        av_frame_remove_side_data(s->frames[0], AV_FRAME_DATA_A53_CC);
+        av_ccfifo_inject(s->cc_fifo, frame);
         frame->pts = s->next_pts++;
         frame->duration = 1;
 
-- 
2.35.1.655.ga68dfadae5

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