Migration from MMAction2 0.x

MMAction2 1.x introduced major refactorings and modifications including some BC-breaking changes. We provide this tutorial to help you migrate your projects from MMAction2 0.x smoothly.

New dependencies

MMAction2 1.x depends on the following packages. You are recommended to prepare a new clean environment and install them according to install tutorial

1. MMEngine: MMEngine is a foundational library for training deep learning model introduced in OpenMMLab 2.0 architecture.

2. MMCV: MMCV is a foundational library for computer vision. MMAction2 1.x requires mmcv>=2.0.0 which is more compact and efficient than mmcv-full==2.0.0.

Configuration files

In MMAction2 1.x, we refactored the structure of configuration files. The configuration files with the old style will be incompatible.

In this section, we will introduce all changes of the configuration files. And we assume you are already familiar with the config files.

Model settings

No changes in model.backbone and model.neck. For model.cls_head, we move the average_clips inside it, which is originally set in model.test_cfg.

Data settings

Changes in data

• The original data field is splited to train_dataloader, val_dataloader and test_dataloader. This allows us to configure them in fine-grained. For example, you can specify different sampler and batch size during training and test.

• The videos_per_gpu is renamed to batch_size.

• The workers_per_gpu is renamed to num_workers.

Original	data = dict( videos_per_gpu=32, workers_per_gpu=2, train=dict(...), val=dict(...), test=dict(...), )
New	train_dataloader = dict( batch_size=32, num_workers=2, dataset=dict(...), sampler=dict(type='DefaultSampler', shuffle=True) # necessary ) val_dataloader = dict( batch_size=32, num_workers=2, dataset=dict(...), sampler=dict(type='DefaultSampler', shuffle=False) # necessary ) test_dataloader = val_dataloader

Changes in pipeline

• The original formatting transforms ToTensor, Collect are combined as PackActionInputs.

• We don’t recommend to do Normalize in the dataset pipeline. Please remove it from pipelines and set it in the model.data_preprocessor field.

Original

train_pipeline = [ dict(type='DecordInit'), dict(type='SampleFrames', clip_len=1, frame_interval=1, num_clips=8), dict(type='DecordDecode'), dict(type='Resize', scale=(-1, 256)), dict( type='MultiScaleCrop', input_size=224, scales=(1, 0.875, 0.75, 0.66), random_crop=False, max_wh_scale_gap=1), dict(type='Resize', scale=(224, 224), keep_ratio=False), dict(type='Flip', flip_ratio=0.5), dict(type='Normalize', **img_norm_cfg), dict(type='FormatShape', input_format='NCHW'), dict(type='Collect', keys=['imgs', 'label'], meta_keys=[]), dict(type='ToTensor', keys=['imgs', 'label']) ]

New

model.data_preprocessor = dict( mean=[123.675, 116.28, 103.53], std=[58.395, 57.12, 57.375], to_rgb=False) train_pipeline = [ dict(type='DecordInit'), dict(type='SampleFrames', clip_len=1, frame_interval=1, num_clips=5), dict(type='DecordDecode'), dict(type='Resize', scale=(-1, 256)), dict( type='MultiScaleCrop', input_size=224, scales=(1, 0.875, 0.75, 0.66), random_crop=False, max_wh_scale_gap=1), dict(type='Resize', scale=(224, 224), keep_ratio=False), dict(type='Flip', flip_ratio=0.5), dict(type='FormatShape', input_format='NCHW'), dict(type='PackActionInputs') ]

Changes in evaluation

• The evaluation field is splited to val_evaluator and test_evaluator. And it won’t support interval and save_best arguments.

• The interval is moved to train_cfg.val_interval and the save_best is moved to default_hooks.checkpoint.save_best.

• The ‘mean_average_precision’, ‘mean_class_accuracy’, ‘mmit_mean_average_precision’, ‘top_k_accuracy’ are combined as AccMetric, and you could use metric_list to specify which metric to calculate.

• The AVAMetric is used to evaluate AVA Dataset.

• The ANetMetric is used to evaluate ActivityNet Dataset.

Original	evaluation = dict( interval=5, metrics=['top_k_accuracy', 'mean_class_accuracy'])
New	val_evaluator = dict( type='AccMetric', metric_list=('top_k_accuracy', 'mean_class_accuracy')) test_evaluator = val_evaluator

Schedule settings

Changes in optimizer and optimizer_config

• Now we use optim_wrapper field to configure the optimization process. And the optimizer becomes a sub field of optim_wrapper.

• paramwise_cfg is also a sub field of optim_wrapper parallel to optimizer.

• optimizer_config is removed now, and all configurations of it are moved to optim_wrapper.

• grad_clip is renamed to clip_grad.

Original	optimizer = dict( type='AdamW', lr=0.0015, weight_decay=0.3, paramwise_cfg = dict( norm_decay_mult=0.0, bias_decay_mult=0.0, )) optimizer_config = dict(grad_clip=dict(max_norm=1.0))
New	optim_wrapper = dict( optimizer=dict(type='AdamW', lr=0.0015, weight_decay=0.3), paramwise_cfg = dict( norm_decay_mult=0.0, bias_decay_mult=0.0, ), clip_gard=dict(max_norm=1.0), )

Changes in lr_config

• The lr_config field is removed and we use new param_scheduler to replace it.

• The warmup related arguments are removed, since we use schedulers combination to implement this functionality.

The new schedulers combination mechanism is very flexible, and you can use it to design many kinds of learning rate / momentum curves.

Original	lr_config = dict( policy='CosineAnnealing', min_lr=0, warmup='linear', warmup_iters=5, warmup_ratio=0.01, warmup_by_epoch=True)
New	param_scheduler = [ # warmup dict( type='LinearLR', start_factor=0.01, by_epoch=True, end=5, # Update the learning rate after every iters. convert_to_iter_based=True), # main learning rate scheduler dict(type='CosineAnnealingLR', by_epoch=True, begin=5), ]

Changes in runner

Most configuration in the original runner field is moved to train_cfg, val_cfg and test_cfg, which configure the loop in training, validation and test.

Original	runner = dict(type='EpochBasedRunner', max_epochs=100)
New	# The `val_interval` is the original `evaluation.interval`. train_cfg = dict(type='EpochBasedTrainLoop', max_epochs=100, val_begin=1, val_interval=1) val_cfg = dict(type='ValLoop') # Use the default validation loop. test_cfg = dict(type='TestLoop') # Use the default test loop.

In fact, in OpenMMLab 2.0, we introduced Loop to control the behaviors in training, validation and test. And the functionalities of Runner are also changed. You can find more details in the MMEngine tutorials.

Runtime settings

Changes in checkpoint_config and log_config

The checkpoint_config are moved to default_hooks.checkpoint and the log_config are moved to default_hooks.logger. And we move many hooks settings from the script code to the default_hooks field in the runtime configuration.

default_hooks = dict(
    # update runtime information, e.g. current iter and lr.
    runtime_info=dict(type='RuntimeInfoHook'),

    # record the time of every iterations.
    timer=dict(type='IterTimerHook'),

    # print log every 100 iterations.
    logger=dict(type='LoggerHook', interval=100),

    # enable the parameter scheduler.
    param_scheduler=dict(type='ParamSchedulerHook'),

    # save checkpoint per epoch, and automatically save the best checkpoint.
    checkpoint=dict(type='CheckpointHook', interval=1, save_best='auto'),

    # set sampler seed in distributed environment.
    sampler_seed=dict(type='DistSamplerSeedHook'),

    # synchronize model buffers at the end of each epoch.
    sync_buffers=dict(type='SyncBuffersHook')
)

In addition, we splited the original logger to logger and visualizer. The logger is used to record information and the visualizer is used to show the logger in different backends, like terminal, TensorBoard and Wandb.

Original	log_config = dict( interval=100, hooks=[ dict(type='TextLoggerHook'), dict(type='TensorboardLoggerHook'), ])
New	default_hooks = dict( ... logger=dict(type='LoggerHook', interval=100), ) visualizer = dict( type='ActionVisualizer', vis_backends=[dict(type='LocalVisBackend'), dict(type='TensorboardVisBackend')], )

Changes in load_from and resume_from

• The resume_from is removed. And we use resume and load_from to replace it.

  • If resume=True and load_from is not None, resume training from the checkpoint in load_from.

  • If resume=True and load_from is None, try to resume from the latest checkpoint in the work directory.

  • If resume=False and load_from is not None, only load the checkpoint, not resume training.

  • If resume=False and load_from is None, do not load nor resume.

Changes in dist_params

The dist_params field is a sub field of env_cfg now. And there are some new configurations in the env_cfg.

env_cfg = dict(
    # whether to enable cudnn benchmark
    cudnn_benchmark=False,

    # set multi process parameters
    mp_cfg=dict(mp_start_method='fork', opencv_num_threads=0),

    # set distributed parameters
    dist_cfg=dict(backend='nccl'),
)

Changes in workflow

Workflow related functionalities are removed.

New field visualizer

The visualizer is a new design in OpenMMLab 2.0 architecture. We use a visualizer instance in the runner to handle results & log visualization and save to different backends.

visualizer = dict(
    type='ActionVisualizer',
    vis_backends=[
        dict(type='LocalVisBackend'),
        # Uncomment the below line to save the log and visualization results to TensorBoard.
        # dict(type='TensorboardVisBackend')
    ]
)

New field default_scope

The start point to search module for all registries. The default_scope in MMAction2 is mmaction. See the registry tutorial for more details.

Packages

mmaction.apis

The documentation can be found here.

Function	Changes
init_recognizer	No changes
inference_recognizer	No changes
train_model	Removed, use runner.train to train.
multi_gpu_test	Removed, use runner.test to test.
single_gpu_test	Removed, use runner.test to test.
set_random_seed	Removed, use mmengine.runner.set_random_seed.
init_random_seed	Removed, use mmengine.dist.sync_random_seed.

mmaction.core

The mmaction.core package is renamed to mmaction.engine.

Sub package	Changes
evaluation	Removed, use the metrics in mmaction.evaluation.
hooks	Moved to mmaction.engine.hooks
optimizer	Moved to mmaction.engine.optimizers
utils	Removed, the distributed environment related functions can be found in the mmengine.dist package.

mmaction.datasets

The documentation can be found here

Changes in BaseActionDataset:

Method	Changes
prepare_train_frames	Replaced by get_data_info
preprare_test_frames	Replaced by get_data_info
evaluate	Removed, use mmengine.evaluator.Evaluator
dump_results	Removed, use mmengine.evaluator.DumpResults
load_annotations	Replaced by load_data_list

Now, you can write a new Dataset class inherited from BaseActionDataset and overwrite load_data_list only. To load more data information, you could overwrite get_data_info like RawframeDataset and AVADataset. The mmaction.datasets.pipelines is renamed to mmaction.datasets.transforms and the mmaction.datasets.pipelines.augmentations is renamed to mmaction.datasets.pipelines.processing.

mmaction.models

The documentation can be found here. The interface of all backbones, necks and losses didn’t change.

Changes in BaseRecognizer:

Method	Changes
extract_feat	Enhanced method, which now supports output features of three stages (backbone, neck, head) and can handle different modes, such as train_mode and test_mode.
forward	Now only accepts three arguments: inputs, data_samples and mode. See the documentation for more details.
forward_train	Replaced by loss.
forward_test	Replaced by predict.
train_step	The optimizer argument is replaced by optim_wrapper and it accepts OptimWrapper.
val_step	The original val_step is the same as train_step, now it calls predict.
test_step	New method, and it's the same as val_step.

Changes in BaseHead:

Method	Changes
forward	No changes
loss	It accepts feats and data_samples instead of cls_score and labels to calculate loss. The data_samples is a list of ActionDataSample.
predict	New method. It accepts feats and data_samples to predict classification scores.

mmaction.utils

Function	Changes
collect_env	No changes
get_root_logger	Removed, use mmengine.MMLogger.get_current_instance
setup_multi_processes	Removed, use mmengine.utils.dl_utils.setup_multi_processes.

Other changes

• We moved the definition of all registries in different packages to the mmaction.registry package.