# Pre Encoding

When training models on encoded latents from a frozen pre-trained autoencoder, the encoder is typically frozen. Because of that, it is common to pre-encode audio to latents and store them on disk instead of computing them on-the-fly during training. This can improve training throughput as well as free up GPU memory that would otherwise be used for encoding.

## Prerequisites

To pre-encode audio to latents, you'll need a dataset config file, an autoencoder model config file, and an **unwrapped** autoencoder checkpoint file.

## Run the Pre Encoding Script

To pre-encode latents from an autoencoder model, you can use `pre_encode.py`. This script will load a pre-trained autoencoder, encode the latents/tokens, and save them to disk in a format that can be easily loaded during training.

The `pre_encode.py` script accepts the following command line arguments:

- `--model-config`
  - Path to model config
- `--ckpt-path`
  - Path to **unwrapped** autoencoder model checkpoint
- `--model-half`
  - If true, uses half precision for model weights
  - Optional
- `--dataset-config`
  - Path to dataset config file
  - Required
- `--output-path`
  - Path to output folder
  - Required
- `--batch-size`
  - Batch size for processing
  - Optional, defaults to 1
- `--sample-size`
  - Number of audio samples to pad/crop to for pre-encoding
  - Optional, defaults to 1320960 (~30 seconds)
- `--is-discrete`
  - If true, treats the model as discrete, saving discrete tokens instead of continuous latents
  - Optional
- `--num-nodes`
  - Number of nodes to use for distributed processing, if available.
  - Optional, defaults to 1
- `--num-workers`
  - Number of dataloader workers
  - Optional, defaults to 4
- `--strategy`
  - PyTorch Lightning strategy
  - Optional, defaults to 'auto'
- `--limit-batches`
  - Limits the number of batches processed
  - Optional
- `--shuffle`
  - If true, shuffles the dataset
  - Optional

For example, if you wanted to encode latents with padding up to 30 seconds long in half precision, you could run the following:

```bash
$ python3 ./pre_encode.py \
--model-config /path/to/model/config.json \
--ckpt-path /path/to/autoencoder/model.ckpt \
--model-half \
--dataset-config /path/to/dataset/config.json \
--output-path /path/to/output/dir \
--sample-size 1320960 \
```

When you run the above, the `--output-path` directory will contain numbered subdirectories for each GPU process used to encode the latents, and a `details.json` file that keeps track of settings used when the script was run.

Inside the numbered subdirectories, you will find the encoded latents as `.npy` files, along with associated `.json` metadata files.

```bash
/path/to/output/dir/
├── 0
│   ├── 0000000000000.json
│   ├── 0000000000000.npy
│   ├── 0000000000001.json
│   ├── 0000000000001.npy
│   ├── 0000000000002.json
│   ├── 0000000000002.npy
...
└── details.json
```

## Training on Pre Encoded Latents

Once you have saved your latents to disk, you can use them to train a model by providing a dataset config file to `train.py` that points to the pre-encoded latents, specifying `"dataset_type"` is `"pre_encoded"`. Under the hood, this will configure a `stable_audio_tools.data.dataset.PreEncodedDataset`.

The dataset config file should look something like this:

```json
{
    "dataset_type": "pre_encoded",
    "datasets": [
        {
            "id": "my_audio",
            "path": "/path/to/output/dir",
            "latent_crop_length": 645
        }
    ],
    "random_crop": false
}
```