ffmpeg: Make CFR frame drop threshold user adjustable

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg.c

@@ -962,7 +962,9 @@ static void do_video_out(AVFormatContext *s,
         }
     case VSYNC_CFR:
         // FIXME set to 0.5 after we fix some dts/pts bugs like in avidec.c
-        if (delta < -1.1)
+        if (frame_drop_threshold && delta < frame_drop_threshold && ost->frame_number) {
+            nb_frames = 0;
+        } else if (delta < -1.1)
             nb_frames = 0;
         else if (delta > 1.1) {
             nb_frames = lrintf(delta);

ffmpeg.h

@@ -482,6 +482,7 @@ extern float dts_error_threshold;
 extern int audio_volume;
 extern int audio_sync_method;
 extern int video_sync_method;
+extern float frame_drop_threshold;
 extern int do_benchmark;
 extern int do_benchmark_all;
 extern int do_deinterlace;

ffmpeg_opt.c

@@ -86,6 +86,7 @@ float dts_error_threshold   = 3600*30;
 int audio_volume      = 256;
 int audio_sync_method = 0;
 int video_sync_method = VSYNC_AUTO;
+float frame_drop_threshold = 0;
 int do_deinterlace    = 0;
 int do_benchmark      = 0;
 int do_benchmark_all  = 0;
@@ -2873,6 +2874,8 @@ const OptionDef options[] = {
         " \"dv\", \"dv50\", \"pal-vcd\", \"ntsc-svcd\", ...)", "type" },
     { "vsync",          HAS_ARG | OPT_EXPERT,                        { opt_vsync },
         "video sync method", "" },
+    { "frame_drop_threshold", HAS_ARG | OPT_FLOAT | OPT_EXPERT,      { &frame_drop_threshold },
+        "frame drop threshold", "" },
     { "async",          HAS_ARG | OPT_INT | OPT_EXPERT,              { &audio_sync_method },
         "audio sync method", "" },
     { "adrift_threshold", HAS_ARG | OPT_FLOAT | OPT_EXPERT,          { &audio_drift_threshold },