diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
index 66a24a1a9c..04de57e41e 100644
--- a/fftools/ffmpeg.c
+++ b/fftools/ffmpeg.c
@@ -1030,6 +1030,79 @@ static void do_subtitle_out(OutputFile *of,
     }
 }
 
+/* Convert frame timestamps to the encoder timebase and decide how many times
+ * should this (and possibly previous) frame be repeated in order to conform to
+ * desired target framerate (if any).
+ */
+static void video_sync_process(OutputFile *of, OutputStream *ost,
+                               AVFrame *next_picture, double duration,
+                               int64_t *nb_frames, int64_t *nb_frames_prev)
+{
+    double delta0, delta;
+
+        double sync_ipts = adjust_frame_pts_to_encoder_tb(of, ost, next_picture);
+        /* delta0 is the "drift" between the input frame (next_picture) and
+         * where it would fall in the output. */
+        delta0 = sync_ipts - ost->next_pts;
+        delta  = delta0 + duration;
+
+        // tracks the number of times the PREVIOUS frame should be duplicated,
+        // mostly for variable framerate (VFR)
+        *nb_frames_prev = 0;
+        /* by default, we output a single frame */
+        *nb_frames = 1;
+
+        if (delta0 < 0 &&
+            delta > 0 &&
+            ost->vsync_method != VSYNC_PASSTHROUGH &&
+            ost->vsync_method != VSYNC_DROP) {
+            if (delta0 < -0.6) {
+                av_log(NULL, AV_LOG_VERBOSE, "Past duration %f too large\n", -delta0);
+            } else
+                av_log(NULL, AV_LOG_DEBUG, "Clipping frame in rate conversion by %f\n", -delta0);
+            sync_ipts = ost->next_pts;
+            duration += delta0;
+            delta0 = 0;
+        }
+
+        switch (ost->vsync_method) {
+        case VSYNC_VSCFR:
+            if (ost->vsync_frame_number == 0 && delta0 >= 0.5) {
+                av_log(NULL, AV_LOG_DEBUG, "Not duplicating %d initial frames\n", (int)lrintf(delta0));
+                delta = duration;
+                delta0 = 0;
+                ost->next_pts = llrint(sync_ipts);
+            }
+        case VSYNC_CFR:
+            // FIXME set to 0.5 after we fix some dts/pts bugs like in avidec.c
+            if (frame_drop_threshold && delta < frame_drop_threshold && ost->vsync_frame_number) {
+                *nb_frames = 0;
+            } else if (delta < -1.1)
+                *nb_frames = 0;
+            else if (delta > 1.1) {
+                *nb_frames = llrintf(delta);
+                if (delta0 > 1.1)
+                    *nb_frames_prev = llrintf(delta0 - 0.6);
+            }
+            next_picture->duration = 1;
+            break;
+        case VSYNC_VFR:
+            if (delta <= -0.6)
+                *nb_frames = 0;
+            else if (delta > 0.6)
+                ost->next_pts = llrint(sync_ipts);
+            next_picture->duration = duration;
+            break;
+        case VSYNC_DROP:
+        case VSYNC_PASSTHROUGH:
+            next_picture->duration = duration;
+            ost->next_pts = llrint(sync_ipts);
+            break;
+        default:
+            av_assert0(0);
+        }
+}
+
 static enum AVPictureType forced_kf_apply(KeyframeForceCtx *kf, AVRational tb,
                                           const AVFrame *in_picture, int dup_idx)
 {
@@ -1089,7 +1162,6 @@ static void do_video_out(OutputFile *of,
     AVCodecContext *enc = ost->enc_ctx;
     AVRational frame_rate;
     int64_t nb_frames, nb_frames_prev, i;
-    double delta, delta0;
     double duration = 0;
     InputStream *ist = ost->ist;
     AVFilterContext *filter = ost->filter->filter;
@@ -1118,67 +1190,8 @@ static void do_video_out(OutputFile *of,
                                               ost->last_nb0_frames[1],
                                               ost->last_nb0_frames[2]);
     } else {
-        double sync_ipts = adjust_frame_pts_to_encoder_tb(of, ost, next_picture);
-        /* delta0 is the "drift" between the input frame (next_picture) and
-         * where it would fall in the output. */
-        delta0 = sync_ipts - ost->next_pts;
-        delta  = delta0 + duration;
-
-        // tracks the number of times the PREVIOUS frame should be duplicated,
-        // mostly for variable framerate (VFR)
-        nb_frames_prev = 0;
-        /* by default, we output a single frame */
-        nb_frames = 1;
-
-        if (delta0 < 0 &&
-            delta > 0 &&
-            ost->vsync_method != VSYNC_PASSTHROUGH &&
-            ost->vsync_method != VSYNC_DROP) {
-            if (delta0 < -0.6) {
-                av_log(NULL, AV_LOG_VERBOSE, "Past duration %f too large\n", -delta0);
-            } else
-                av_log(NULL, AV_LOG_DEBUG, "Clipping frame in rate conversion by %f\n", -delta0);
-            sync_ipts = ost->next_pts;
-            duration += delta0;
-            delta0 = 0;
-        }
-
-        switch (ost->vsync_method) {
-        case VSYNC_VSCFR:
-            if (ost->vsync_frame_number == 0 && delta0 >= 0.5) {
-                av_log(NULL, AV_LOG_DEBUG, "Not duplicating %d initial frames\n", (int)lrintf(delta0));
-                delta = duration;
-                delta0 = 0;
-                ost->next_pts = llrint(sync_ipts);
-            }
-        case VSYNC_CFR:
-            // FIXME set to 0.5 after we fix some dts/pts bugs like in avidec.c
-            if (frame_drop_threshold && delta < frame_drop_threshold && ost->vsync_frame_number) {
-                nb_frames = 0;
-            } else if (delta < -1.1)
-                nb_frames = 0;
-            else if (delta > 1.1) {
-                nb_frames = llrintf(delta);
-                if (delta0 > 1.1)
-                    nb_frames_prev = llrintf(delta0 - 0.6);
-            }
-            next_picture->duration = 1;
-            break;
-        case VSYNC_VFR:
-            if (delta <= -0.6)
-                nb_frames = 0;
-            else if (delta > 0.6)
-                ost->next_pts = llrint(sync_ipts);
-            next_picture->duration = duration;
-            break;
-        case VSYNC_DROP:
-        case VSYNC_PASSTHROUGH:
-            next_picture->duration = duration;
-            ost->next_pts = llrint(sync_ipts);
-            break;
-        default:
-            av_assert0(0);
-        }
+        video_sync_process(of, ost, next_picture, duration,
+                           &nb_frames, &nb_frames_prev);
     }
 
     memmove(ost->last_nb0_frames + 1,