test(video): add test cases for variable framerate videos

test/generate_reference_resources.sh

@@ -77,3 +77,22 @@ do
   python3 "$TORCHCODEC_PATH/test/convert_image_to_tensor.py" "$bmp"
   rm -f "$bmp"
 done
+
+# This video was generated by running the following:
+# ffmpeg -f lavfi -i testsrc=duration=10:size=128x128:rate=30        -vf "setpts=PTS*if(gt(N\,30)\,1.5\,1)" -c:v libx264 -bf 0 var_fps_video.mp4
+VIDEO_PATH=$RESOURCES_DIR/var_fps_video.mp4
+STREAMS=(0)
+
+FRAMES=(0 1 2 3 4 5 10 15 20 25 30 35 40 45 50 55 60)
+for stream in "${STREAMS[@]}"; do
+  for frame in "${FRAMES[@]}"; do
+    frame_name=$(printf "%06d" "$frame")
+    ffmpeg -y -i "$VIDEO_PATH" -map 0:"$stream" -vf select="eq(n\,$frame)" -vsync vfr -q:v 2 "$VIDEO_PATH.stream$stream.frame$frame_name.bmp"
+  done
+done
+
+for bmp in "$RESOURCES_DIR"/*.bmp
+do
+  python3 "$TORCHCODEC_PATH/test/convert_image_to_tensor.py" "$bmp"
+  rm -f "$bmp"
+done