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---
comments: true
description: Learn how to utilize callbacks in the Ultralytics framework during train, val, export, and predict modes for enhanced functionality.
keywords: Ultralytics, YOLO, callbacks guide, training callback, validation callback, export callback, prediction callback
---
## Callbacks
Ultralytics framework supports callbacks as entry points in strategic stages of train, val, export, and predict modes.
Each callback accepts a `Trainer`, `Validator`, or `Predictor` object depending on the operation type. All properties of
these objects can be found in Reference section of the docs.
## Examples
### Returning additional information with Prediction
In this example, we want to return the original frame with each result object. Here's how we can do that
```python
def on_predict_batch_end(predictor):
# Retrieve the batch data
_, im0s, _, _ = predictor.batch
# Ensure that im0s is a list
im0s = im0s if isinstance(im0s, list) else [im0s]
# Combine the prediction results with the corresponding frames
predictor.results = zip(predictor.results, im0s)
# Create a YOLO model instance
model = YOLO(f'yolov8n.pt')
# Add the custom callback to the model
model.add_callback("on_predict_batch_end", on_predict_batch_end)
# Iterate through the results and frames
for (result, frame) in model.track/predict():
pass
```
## All callbacks
Here are all supported callbacks. See callbacks [source code](https://github.com/ultralytics/ultralytics/blob/main/ultralytics/utils/callbacks/base.py) for additional details.
### Trainer Callbacks
| Callback | Description |
|-----------------------------|---------------------------------------------------------|
| `on_pretrain_routine_start` | Triggered at the beginning of pre-training routine |
| `on_pretrain_routine_end` | Triggered at the end of pre-training routine |
| `on_train_start` | Triggered when the training starts |
| `on_train_epoch_start` | Triggered at the start of each training epoch |
| `on_train_batch_start` | Triggered at the start of each training batch |
| `optimizer_step` | Triggered during the optimizer step |
| `on_before_zero_grad` | Triggered before gradients are zeroed |
| `on_train_batch_end` | Triggered at the end of each training batch |
| `on_train_epoch_end` | Triggered at the end of each training epoch |
| `on_fit_epoch_end` | Triggered at the end of each fit epoch |
| `on_model_save` | Triggered when the model is saved |
| `on_train_end` | Triggered when the training process ends |
| `on_params_update` | Triggered when model parameters are updated |
| `teardown` | Triggered when the training process is being cleaned up |
### Validator Callbacks
| Callback | Description |
|----------------------|-------------------------------------------------|
| `on_val_start` | Triggered when the validation starts |
| `on_val_batch_start` | Triggered at the start of each validation batch |
| `on_val_batch_end` | Triggered at the end of each validation batch |
| `on_val_end` | Triggered when the validation ends |
### Predictor Callbacks
| Callback | Description |
|------------------------------|---------------------------------------------------|
| `on_predict_start` | Triggered when the prediction process starts |
| `on_predict_batch_start` | Triggered at the start of each prediction batch |
| `on_predict_postprocess_end` | Triggered at the end of prediction postprocessing |
| `on_predict_batch_end` | Triggered at the end of each prediction batch |
| `on_predict_end` | Triggered when the prediction process ends |
### Exporter Callbacks
| Callback | Description |
|-------------------|------------------------------------------|
| `on_export_start` | Triggered when the export process starts |
| `on_export_end` | Triggered when the export process ends |