[Feature]: Video demo (#4420)

* Demo with cv2.VideoCapture

Signed-off-by: steven0129 <h3584935@gmail.com>

* Add video demo and docs

* Use ProgressBar

* add demo.mp4 and docs

* Use mmcv.VideoReader

* Use track_iter_progress

Co-authored-by: hhaAndroid <1286304229@qq.com>

demo/video_demo.py

+import argparse
+
+import cv2
+import mmcv
+
+from mmdet.apis import inference_detector, init_detector
+
+
+def parse_args():
+    parser = argparse.ArgumentParser(description='MMDetection video demo')
+    parser.add_argument('video', help='Video file')
+    parser.add_argument('config', help='Config file')
+    parser.add_argument('checkpoint', help='Checkpoint file')
+    parser.add_argument(
+        '--device', default='cuda:0', help='Device used for inference')
+    parser.add_argument(
+        '--score-thr', type=float, default=0.3, help='Bbox score threshold')
+    parser.add_argument('--out', type=str, help='Output video file')
+    parser.add_argument('--show', action='store_true', help='Show video')
+    parser.add_argument(
+        '--wait-time',
+        type=float,
+        default=1,
+        help='The interval of show (s), 0 is block')
+    args = parser.parse_args()
+    return args
+
+
+def main():
+    args = parse_args()
+    assert args.out or args.show, \
+        ('Please specify at least one operation (save/show the '
+         'video) with the argument "--out" or "--show"')
+
+    model = init_detector(args.config, args.checkpoint, device=args.device)
+
+    video_reader = mmcv.VideoReader(args.video)
+    video_writer = None
+    if args.out:
+        fourcc = cv2.VideoWriter_fourcc(*'mp4v')
+        video_writer = cv2.VideoWriter(
+            args.out, fourcc, video_reader.fps,
+            (video_reader.width, video_reader.height))
+
+    for frame in mmcv.track_iter_progress(video_reader):
+        result = inference_detector(model, frame)
+        frame = model.show_result(frame, result, score_thr=args.score_thr)
+        if args.show:
+            cv2.namedWindow('video', 0)
+            mmcv.imshow(frame, 'video', args.wait_time)
+        if args.out:
+            video_writer.write(frame)
+
+    if video_writer:
+        video_writer.release()
+    cv2.destroyAllWindows()
+
+
+if __name__ == '__main__':
+    main()

docs/1_exist_data_model.md

@@ -91,7 +91,7 @@ asyncio.run(main())
 
 ### Demos
 
-We also provide two demo scripts, implemented with high-level APIs and supporting functionality codes.
+We also provide three demo scripts, implemented with high-level APIs and supporting functionality codes.
 Source codes are available [here](https://github.com/open-mmlab/mmdetection/tree/master/demo).
 
 #### Image demo
@@ -111,7 +111,7 @@ Examples:
 
 ```shell
 python demo/image_demo.py demo/demo.jpg \
-    configs/faster_rcnn_r50_fpn_1x_coco.py \
+    configs/faster_rcnn/faster_rcnn_r50_fpn_1x_coco.py \
     checkpoints/faster_rcnn_r50_fpn_1x_coco_20200130-047c8118.pth \
     --device cpu
 ```
@@ -133,10 +133,35 @@ Examples:
 
 ```shell
 python demo/webcam_demo.py \
-    configs/faster_rcnn_r50_fpn_1x_coco.py \
+    configs/faster_rcnn/faster_rcnn_r50_fpn_1x_coco.py \
     checkpoints/faster_rcnn_r50_fpn_1x_coco_20200130-047c8118.pth
 ```
 
+#### Video demo
+
+This script performs inference on a video.
+
+```shell
+python demo/video_demo.py \
+    ${VIDEO_FILE} \
+    ${CONFIG_FILE} \
+    ${CHECKPOINT_FILE} \
+    [--device ${GPU_ID}] \
+    [--score-thr ${SCORE_THR}] \
+    [--out ${OUT_FILE}] \
+    [--show] \
+    [--wait-time ${WAIT_TIME}]
+```
+
+Examples:
+
+```shell
+python demo/video_demo.py demo/demo.mp4 \
+    configs/faster_rcnn/faster_rcnn_r50_fpn_1x_coco.py \
+    checkpoints/faster_rcnn_r50_fpn_1x_coco_20200130-047c8118.pth \
+    --out result.mp4
+```
+
 ## Test existing models on standard datasets
 
 To evaluate a model's accuracy, one usually tests the model on some standard datasets.