Merge branch 'tjq/sthv2_doc' into 'master'

Add sthv2 doc.

See merge request open-mmlab/mmaction-lite!294

tools/data/mit/extract_frames.sh

 #! /usr/bin/bash env
 
 cd ../
-python build_rawframes.py ../../data/mit/videos/training ../../data/mit/rawframes/training/ --level 2 --flow_type tvl1 --ext mp4 --task both 
+python build_rawframes.py ../../data/mit/videos/training ../../data/mit/rawframes/training/ --level 2 --flow_type tvl1 --ext mp4 --task both
 echo "Raw frames (RGB and tv-l1) Generated for train set"
 
-python build_rawframes.py ../../data/mit/vides/validation/ ../../data/mit/rawframes/validation/ --level 2 --flow_type tvl1 --ext mp4 --task both 
+python build_rawframes.py ../../data/mit/vides/validation/ ../../data/mit/rawframes/validation/ --level 2 --flow_type tvl1 --ext mp4 --task both
 echo "Raw frames (RGB and tv-l1) Generated for val set"
 
 cd mit/

tools/data/sthv2/extract_frames.sh

+#! /usr/bin/bash env
+
+FLOW_TYPE=$1
+
+cd ../
+python build_rawframes.py ../../data/sthv2/videos/ ../../data/sthv2/rawframes/ --task both --level 1 --flow_type ${FLOW_TYPE} --ext webm
+echo "Raw frames (RGB and tv-l1) Generated"
+cd sthv2/

tools/data/sthv2/extract_rgb_frames.sh

+#! /usr/bin/bash env
+
+cd ../
+python build_rawframes.py ../../data/sthv2/videos/ ../../data/sthv2/rawframes/ --task rgb --level 1  --ext webm
+echo "Genearte raw frames (RGB only)"
+
+cd sthv2/

tools/data/sthv2/generate_rawframes_filelist.sh

+#! /usr/bin/bash env
+
+cd ../../../
+PYTHONPATH=. python tools/data/build_file_list.py sthv2 data/sthv2/rawframes/ --num_split 1 --level 1 --subset train --format rawframe --shuffle
+PYTHONPATH=. python tools/data/build_file_list.py sthv2 data/sthv2/rawframes/ --num_split 1 --level 1 --subset val --format rawframe --shuffle
+echo "Filelist for rawframes generated."
+
+cd tools/data/sthv2/

tools/data/sthv2/generate_videos_filelist.sh

+#! /usr/bin/bash env
+
+cd ../../../
+PYTHONPATH=. python tools/data/build_file_list.py sthv2 data/sthv2/videos/ --num_split 1 --level 1 --subset train --format videos --shuffle
+PYTHONPATH=. python tools/data/build_file_list.py sthv2 data/sthv2/videos/ --num_split 1 --level 1 --subset val --format videos --shuffle
+echo "Filelist for videos generated."
+
+cd tools/data/sthv2/

tools/data/sthv2/preparing_sthv2.md

+# Preparing Something-Something V2
+
+For basic dataset information, you can refer to the dataset [website](https://20bn.com/datasets/something-something/v2).
+Before we start, please make sure that the directory is located at `$MMACTION/tools/data/sthv2/`.
+
+## Step 1. Prepare Annotations
+
+First of all, you have to sign in and download annotations to `$MMACTION/data/sthv2/annotations` on the official [website](https://20bn.com/datasets/something-something/v2).
+
+## Step 2. Prepare Videos
+
+Then, you can download all data parts to `$MMACTION/data/sthv2/` and use the following command to extract.
+
+```shell
+cd $MMACTION/data/sthv2/
+cat 20bn-something-something-v2-?? | tar zx
+```
+
+## Step 3. Extract RGB and Flow
+
+This part is **optional** if you only want to use the video loader.
+
+Before extracting, please refer to [install.md](/docs/install.md) for installing [dense_flow](https://github.com/innerlee/denseflow).
+
+If you have plenty of SSD space, then we recommend extracting frames there for better I/O performance.
+
+You can run the following script to soft link SSD.
+
+```shell
+# execute these two line (Assume the SSD is mounted at "/mnt/SSD/")
+mkdir /mnt/SSD/sthv2_extracted/
+ln -s /mnt/SSD/sthv2_extracted/ ../../../data/sthv2/rawframes
+
+If you didn't install dense_flow in the installation or only want to play with RGB frames (since extracting optical flow can be time-comsuming), consider running the following script to extract **RGB-only** frames.
+
+```shell
+cd $MMACTION/tools/data/sthv2/
+bash extract_rgb_frames.sh
+```
+
+If both are required, run the following script to extract frames.
+
+```shell
+cd $MMACTION/tools/data/sthv2/
+bash extract_frames.sh tvl1
+```
+
+## Step 4. Generate File List
+
+you can run the follow script to generate file list in the format of rawframes and videos.
+
+```shell
+cd $MMACTION/tools/data/sthv2/
+bash generate_filelist.sh
+```
+
+## Step 5. Check Directory Structure
+
+After the whole data process for Something-Something V2 preparation,
+you will get the rawframes (RGB + Flow), videos and annotation files for Something-Something V2.
+
+In the context of the whole project (for Something-Something V2 only), the folder structure will look like:
+
+```
+mmaction
+├── mmaction
+├── tools
+├── configs
+├── data
+│   ├── sthv2
+│   │   ├── sthv2_{train,val}_list_rawframes.txt
+│   │   ├── sthv2_{train,val}_list_videos.txt
+│   │   ├── annotations
+│   |   ├── videos
+│   |   |   ├── 100000.mp4
+│   |   |   ├── 100001.mp4
+│   |   |   ├──...
+│   |   ├── rawframes
+│   |   |   ├── 100000
+│   |   |   |   ├── img_00001.jpg
+│   |   |   |   ├── img_00002.jpg
+│   |   |   |   ├── ...
+│   |   |   |   ├── flow_x_00001.jpg
+│   |   |   |   ├── flow_x_00002.jpg
+│   |   |   |   ├── ...
+│   |   |   |   ├── flow_y_00001.jpg
+│   |   |   |   ├── flow_y_00002.jpg
+│   |   |   |   ├── ...
+│   |   |   ├── 100001
+│   |   |   ├── ...
+
+```
+
+For training and evaluating on Something-Something V2, please refer to [getting_started.md](/docs/getting_started.md).