[Bug] multi-frame inference in demo/body3d_pose_lifter_demo.py

[unrealMJ]

Prerequisite

• I have searched Issues and Discussions but cannot get the expected help.
• The bug has not been fixed in the latest version(https://github.com/open-mmlab/mmpose).

Environment

Reproduces the problem - code sample

python  demo/body3d_pose_lifter_demo.py  \
demo/mmdetection_cfg/faster_rcnn_r50_fpn_coco.py \
https://download.openmmlab.com/mmdetection/v2.0/faster_rcnn/faster_rcnn_r50_fpn_1x_coco/faster_rcnn_r50_fpn_1x_coco_20200130-047c8118.pth  \
configs/body_2d_keypoint/topdown_heatmap/posetrack18/td-hm_hrnet-w48_8xb64-20e_posetrack18-384x288.py \
https://download.openmmlab.com/mmpose/top_down/hrnet/hrnet_w48_posetrack18_384x288-5fd6d3ff_20211130.pth  \
configs/body_3d_keypoint/pose_lift/h36m/pose-lift_videopose3d-243frm-supv-cpn-ft_8xb128-200e_h36m.py \
https://download.openmmlab.com/mmpose/body3d/videopose/videopose_h36m_243frames_fullconv_supervised_cpn_ft-88f5abbb_20210527.pth  \
--input https://user-images.githubusercontent.com/87690686/164970135-b14e424c-765a-4180-9bc8-fa8d6abc5510.mp4 \
--output-root  vis_results  \
--use-multi-frames

Reproduces the problem - command or script

python  demo/body3d_pose_lifter_demo.py  \
demo/mmdetection_cfg/faster_rcnn_r50_fpn_coco.py \
https://download.openmmlab.com/mmdetection/v2.0/faster_rcnn/faster_rcnn_r50_fpn_1x_coco/faster_rcnn_r50_fpn_1x_coco_20200130-047c8118.pth  \
configs/body_2d_keypoint/topdown_heatmap/posetrack18/td-hm_hrnet-w48_8xb64-20e_posetrack18-384x288.py \
https://download.openmmlab.com/mmpose/top_down/hrnet/hrnet_w48_posetrack18_384x288-5fd6d3ff_20211130.pth  \
configs/body_3d_keypoint/pose_lift/h36m/pose-lift_videopose3d-243frm-supv-cpn-ft_8xb128-200e_h36m.py \
https://download.openmmlab.com/mmpose/body3d/videopose/videopose_h36m_243frames_fullconv_supervised_cpn_ft-88f5abbb_20210527.pth  \
--input https://user-images.githubusercontent.com/87690686/164970135-b14e424c-765a-4180-9bc8-fa8d6abc5510.mp4 \
--output-root  vis_results  \
--use-multi-frames

Reproduces the problem - error message

Traceback (most recent call last):
File "/mnt/petrelfs/majie/project/openmmlab/mmpose/demo/body3d_pose_lifter_demo.py", line 569, in
main()
File "/mnt/petrelfs/majie/project/openmmlab/mmpose/demo/body3d_pose_lifter_demo.py", line 395, in main
assert 'frame_indices' in pose_estimator.cfg.test_dataloader.dataset
AssertionError

Additional information

1. the parser doesn't contain the --online option, see line 498 in body3d_pose_lifter_demo.py
2. reference docs https://github.com/open-mmlab/mmpose/blob/dev-1.x/demo/docs/en/3d_human_pose_demo.md

[unrealMJ]

Besides, the body3d_pose_lifter_demo.py can't visualize pose in branch dev-1.x

This is main branch:

This is dev-1.x branch:

[Tau-J]

Thanks for you feedback. We will fix it in #2594 .