diff --git a/data/negative-timestamps.ts b/data/negative-timestamps.ts
new file mode 100644
index 0000000000..0f1cdf117b
Binary files /dev/null and b/data/negative-timestamps.ts differ
diff --git a/ffmpeg/filter.c b/ffmpeg/filter.c
index d9824cb23b..643b113229 100644
--- a/ffmpeg/filter.c
+++ b/ffmpeg/filter.c
@@ -343,6 +343,24 @@ int filtergraph_write(AVFrame *inf, struct input_ctx *ictx, struct output_ctx *o
         // So in this case just increment the pts by 1/fps
         ts_step = av_rescale_q_rnd(1, av_inv_q(octx->fps), vst->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
       }
+
+      // Check for negative timestamp steps and use a default frame duration instead
+      if (ts_step < 0) {
+        int64_t frame_duration = av_rescale_q_rnd(1, av_inv_q(octx->fps), vst->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
+        av_log(NULL, AV_LOG_WARNING, "Detected negative timestamp step (%lld) at PTS %lld. Using frame duration (%lld) instead.\n", 
+               (long long)ts_step, (long long)inf->pts, (long long)frame_duration);
+        ts_step = frame_duration;
+      }
+
+      // Check for abnormal positive steps
+      int64_t max_reasonable_step = av_rescale_q_rnd(10, av_inv_q(octx->fps), vst->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
+      if (ts_step > max_reasonable_step) {
+        int64_t frame_duration = av_rescale_q_rnd(1, av_inv_q(octx->fps), vst->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
+        av_log(NULL, AV_LOG_WARNING, "Detected abnormal timestamp step (%lld) at PTS %lld. Using frame duration (%lld) instead.\n", 
+               (long long)ts_step, (long long)inf->pts, (long long)frame_duration);
+        ts_step = frame_duration;
+      }
+
       filter->custom_pts += ts_step;
       filter->prev_frame_pts = inf->pts;
     } else {
@@ -366,7 +384,7 @@ int filtergraph_write(AVFrame *inf, struct input_ctx *ictx, struct output_ctx *o
 
   if (inf) {
     // Apply the custom pts, then reset for the next output
-    int old_pts = inf->pts;
+    uint64_t old_pts = inf->pts;
     inf->pts = filter->custom_pts;
     ret = av_buffersrc_write_frame(filter->src_ctx, inf);
     inf->pts = old_pts;
diff --git a/ffmpeg/timestamp_test.go b/ffmpeg/timestamp_test.go
new file mode 100644
index 0000000000..1b78d7a419
--- /dev/null
+++ b/ffmpeg/timestamp_test.go
@@ -0,0 +1,80 @@
+package ffmpeg
+
+import (
+	"os"
+	"testing"
+	"time"
+)
+
+// Tests fix for VFR inputs causing infinite frame duplication, resulting in huge output files.
+func TestTimestampRegression(t *testing.T) {
+	InitFFmpeg()
+
+	inputFile := "../data/negative-timestamps.ts"
+	if _, err := os.Stat(inputFile); err != nil {
+		t.Skip("Problematic input file not available")
+	}
+
+	// Test the exact pattern that triggered infinite loops:
+	// passthrough FPS followed by 30fps conversion
+	passthroughProfile := P240p30fps16x9
+	passthroughProfile.Framerate = 0 // passthrough
+
+	options := []TranscodeOptions{
+		{
+			Oname:        "test_passthrough.mp4",
+			Accel:        Software,
+			Profile:      passthroughProfile,
+			AudioEncoder: ComponentOptions{Name: "drop"},
+		},
+		{
+			Oname:        "test_30fps.mp4",
+			Accel:        Software,
+			Profile:      P240p30fps16x9,
+			AudioEncoder: ComponentOptions{Name: "drop"},
+		},
+	}
+
+	// Should complete quickly with fix, would hang without it
+	done := make(chan error, 1)
+	var result *TranscodeResults
+
+	go func() {
+		var err error
+		result, err = Transcode3(&TranscodeOptionsIn{
+			Fname: inputFile,
+			Accel: Software,
+		}, options)
+		done <- err
+	}()
+
+	select {
+	case err := <-done:
+		if err != nil {
+			// Size limit error means protection worked
+			if err == ErrTranscoderOutputSize {
+				t.Log("Size limit triggered")
+				return
+			}
+			t.Fatal(err)
+		}
+
+		if result == nil {
+			t.Fatal("No result")
+		}
+
+		// Verify outputs are reasonably sized (not 20-190GB)
+		for _, opt := range options {
+			if stat, err := os.Stat(opt.Oname); err == nil {
+				size := stat.Size()
+				if size > 10*1024*1024 { // 10MB is suspicious for this input
+					t.Errorf("%s too large: %d bytes", opt.Oname, size)
+				}
+				os.Remove(opt.Oname)
+			}
+		}
+
+	case <-time.After(30 * time.Second):
+		t.Fatal("Hung for 30s - infinite loop detected")
+	}
+}