Customize Dataset

In this tutorial, we will introduce some methods about how to customize your own dataset by online conversion.

General understanding of the Dataset in MMAction2

MMAction2 provides task-specific Dataset class, e.g. VideoDataset/RawframeDataset for action recognition, AVADataset for spatio-temporal action detection, PoseDataset for skeleton-based action recognition. These task-specific datasets only require the implementation of load_data_list(self) for generating a data list from the annotation file. The remaining functions are automatically handled by the superclass (i.e., BaseActionDataset and BaseDataset). The following table shows the inheritance relationship and the main method of the modules.

Class Name Class Method
MMAction2::VideoDataset load_data_list(self)
Build data list from the annotation file.
MMAction2::BaseActionDataset get_data_info(self, idx)
Given the idx, return the corresponding data sample from the data list.
MMEngine::BaseDataset __getitem__(self, idx)
Given the idx, call get_data_info to get the data sample, then call the pipeline to perform transforms and augmentation in train_pipeline or val_pipeline .

Customize new datasets

Although offline conversion is the preferred method for utilizing your own data in most cases, MMAction2 offers a convenient process for creating a customized Dataset class. As mentioned previously, task-specific datasets only require the implementation of load_data_list(self) for generating a data list from the annotation file. It is noteworthy that the elements in the data_list are dict with fields that are essential for the subsequent processes in the pipeline.

Taking VideoDataset as an example, train_pipeline/val_pipeline require 'filename' in DecordInit and 'label' in PackActionInputs. Consequently, the data samples in the data_list must contain 2 fields: 'filename' and 'label'. Please refer to customize pipeline for more details about the pipeline.

data_list.append(dict(filename=filename, label=label))

However, AVADataset is more complex, data samples in the data_list consist of several fields about the video data. Moreover, it overwrites get_data_info(self, idx) to convert keys that are indispensable in the spatio-temporal action detection pipeline.

class AVADataset(BaseActionDataset):

  def load_data_list(self) -> List[dict]:
        video_info = dict(
      return data_list

  def get_data_info(self, idx: int) -> dict:
      ann = data_info.pop('ann')
      data_info['gt_bboxes'] = ann['gt_bboxes']
      data_info['gt_labels'] = ann['gt_labels']
      data_info['entity_ids'] = ann['entity_ids']
      return data_info

Customize keypoint format for PoseDataset

MMAction2 currently supports three keypoint formats: coco, nturgb+d and openpose. If you use one of these formats, you may simply specify the corresponding format in the following modules:

For Graph Convolutional Networks, such as AAGCN, STGCN, …

  • pipeline: argument dataset in JointToBone.

  • backbone: argument graph_cfg in Graph Convolutional Networks.

For PoseC3D:

  • pipeline: In Flip, specify left_kp and right_kp based on the symmetrical relationship between keypoints.

  • pipeline: In GeneratePoseTarget, specify skeletons, left_limb, right_limb if with_limb is True, and left_kp, right_kp if with_kp is True.

If using a custom keypoint format, it is necessary to include a new graph layout in both the backbone and pipeline. This layout will define the keypoints and their connection relationship.

Taking the coco dataset as an example, we define a layout named coco in Graph. The inward connections of this layout comprise all node connections, with each centripetal connection consisting of a tuple of nodes. Additional settings for coco include specifying the number of nodes as 17 the node 0 as the central node.

self.num_node = 17
self.inward = [(15, 13), (13, 11), (16, 14), (14, 12), (11, 5),
                (12, 6), (9, 7), (7, 5), (10, 8), (8, 6), (5, 0),
                (6, 0), (1, 0), (3, 1), (2, 0), (4, 2)] = 0

Similarly, we define the pairs in JointToBone, adding a bone of (0, 0) to align the number of bones to the nodes. The pairs of coco dataset are shown below, and the order of pairs in JointToBone is irrelevant.

self.pairs = ((0, 0), (1, 0), (2, 0), (3, 1), (4, 2), (5, 0),
              (6, 0), (7, 5), (8, 6), (9, 7), (10, 8), (11, 0),
              (12, 0), (13, 11), (14, 12), (15, 13), (16, 14))

To use your custom keypoint format, simply define the aforementioned settings as your graph structure and specify them in your config file as shown below, In this example, we will use STGCN, with n denoting the number of classes and custom_dataset defined in Graph and JointToBone.

model = dict(
      type='STGCN', graph_cfg=dict(layout='custom_dataset', mode='stgcn_spatial')),
  cls_head=dict(type='GCNHead', num_classes=n, in_channels=256))

train_pipeline = [
  dict(type='GenSkeFeat', dataset='custom_dataset'),

val_pipeline = [
  dict(type='GenSkeFeat', dataset='custom_dataset'),

test_pipeline = [
  dict(type='GenSkeFeat', dataset='custom_dataset'),

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