input video for demo, but got KeyError：“Non-existent config key：DEMO.INPUT_VIDEO”

I want to input video for demo, so I change DEMO.DATA_SOURCE to my video path, run:
` python tools/run_net.py --cfg demo/AVA/SLOWFAST_32x2_R101_50_50.yaml`

but I got:

**ValueError: Type mismatch ( vs. ) with values (0 vs. ./fight2.mp4) for config key: DEMO.DATA_SOURCE**

Traceback
File "tools/run_net.py", line 37, in
main()
File "tools/run_net.py", line 19, in main
cfg = load_config(args)
File "/home/nd/slowfast/slowfast/utils/parser.py", line 78, in load_config
cfg.merge_from_file(args.cfg_file)
File "/home/nd/anaconda3/envs/SlowFast/lib/python3.6/site-packages/fvcore/common/config.py", line 109, in merge_from_file
self.merge_from_other_cfg(loaded_cfg)
File "/home/nd/anaconda3/envs/SlowFast/lib/python3.6/site-packages/fvcore/common/config.py", line 120, in merge_from_other_cfg
return super().merge_from_other_cfg(cfg_other)
File "/home/nd/anaconda3/envs/SlowFast/lib/python3.6/site-packages/yacs/config.py", line 217, in merge_from_other_cfg
_merge_a_into_b(cfg_other, self, self, [])
File "/home/nd/anaconda3/envs/SlowFast/lib/python3.6/site-packages/yacs/config.py", line 464, in _merge_a_into_b
_merge_a_into_b(v, b[k], root, key_list + [k])
File "/home/nd/anaconda3/envs/SlowFast/lib/python3.6/site-packages/yacs/config.py", line 460, in _merge_a_into_b
v = _check_and_coerce_cfg_value_type(v, b[k], k, full_key)
File "/home/nd/anaconda3/envs/SlowFast/lib/python3.6/site-packages/yacs/config.py", line 517, in _check_and_coerce_cfg_value_type
original_type, replacement_type, original, replacement, full_key
ValueError: Type mismatch ( vs. ) with values (0 vs. ./fight2.mp4) for config key: DEMO.DATA_SOURCE

So I change add INPUT_VIDEO in DEMO part: INPUT_VIDEO:"./fight2.mp4"

then I got

**KeyError：“Non-existent config key：DEMO.INPUT_VIDEO”**

Any help would be appreciated

here is my config file:

slowfast/demo/AVA/SLOWFAST_32x2_R101_50_50.yaml

```yaml
TRAIN:
ENABLE: False
DATASET: ava
BATCH_SIZE: 16
EVAL_PERIOD: 1
CHECKPOINT_PERIOD: 1
AUTO_RESUME: True
CHECKPOINT_FILE_PATH: "./SLOWFAST_32x2_R101_50_50.pkl" #path to pretrain model
CHECKPOINT_TYPE: pytorch
DATA:
NUM_FRAMES: 32
SAMPLING_RATE: 2
TRAIN_JITTER_SCALES: [256, 320]
TRAIN_CROP_SIZE: 224
TEST_CROP_SIZE: 256
INPUT_CHANNEL_NUM: [3, 3]
DETECTION:
ENABLE: True
ALIGNED: False
AVA:
BGR: False
DETECTION_SCORE_THRESH: 0.8
TEST_PREDICT_BOX_LISTS: ["person_box_67091280_iou90/ava_detection_val_boxes_and_labels.csv"]
SLOWFAST:
ALPHA: 4
BETA_INV: 8
FUSION_CONV_CHANNEL_RATIO: 2
FUSION_KERNEL_SZ: 5
RESNET:
ZERO_INIT_FINAL_BN: True
WIDTH_PER_GROUP: 64
NUM_GROUPS: 1
DEPTH: 101
TRANS_FUNC: bottleneck_transform
STRIDE_1X1: False
NUM_BLOCK_TEMP_KERNEL: [[3, 3], [4, 4], [6, 6], [3, 3]]
SPATIAL_DILATIONS: [[1, 1], [1, 1], [1, 1], [2, 2]]
SPATIAL_STRIDES: [[1, 1], [2, 2], [2, 2], [1, 1]]
NONLOCAL:
LOCATION: [[[], []], [[], []], [[6, 13, 20], []], [[], []]]
GROUP: [[1, 1], [1, 1], [1, 1], [1, 1]]
INSTANTIATION: dot_product
POOL: [[[2, 2, 2], [2, 2, 2]], [[2, 2, 2], [2, 2, 2]], [[2, 2, 2], [2, 2, 2]], [[2, 2, 2], [2, 2, 2]]]
MODEL:
NUM_CLASSES: 80
ARCH: slowfast
LOSS_FUNC: bce
DROPOUT_RATE: 0.5
HEAD_ACT: sigmoid
TEST:
ENABLE: False
DATASET: ava
BATCH_SIZE: 8
DATA_LOADER:
NUM_WORKERS: 2
PIN_MEMORY: True
DEMO:
ENABLE: True
LABEL_FILE_PATH: "./demo/AVA/ava.names"
DATA_SOURCE: "./fight2.mp4"
# INPUT_VIDEO: "./fight2.mp4"
OUTPUT_FILE: "./output.mp4"

# DISPLAY_WIDTH: 640
# DISPLAY_HEIGHT: 480
DETECTRON2_OBJECT_DETECTION_MODEL_CFG: "COCO-Detection/faster_rcnn_R_50_FPN_3x.yaml"
DETECTRON2_OBJECT_DETECTION_MODEL_WEIGHTS: "/home/nd/slowfast/demo/AVA/model_final_280758.pkl"

# DETECTRON2_OBJECT_DETECTION_MODEL_WEIGHTS: "detectron2://COCO-Detection/faster_rcnn_R_50_FPN_3x/137849458/model_final_280758.pkl"

NUM_GPUS: 1
NUM_SHARDS: 1
RNG_SEED: 0
OUTPUT_DIR: .

```

any help would be appreciated!