Encodec (#991)

* initial encodec

* works

* nits

* use fast group norm

* fix for rnn layer

* fix mlx version

* use custom LSTM kernel

* audio encodec

* fix example, support batched inference

* nits

encodec/README.md

@@ -0,0 +1,83 @@
+# EnCodec
+
+An example of Meta's EnCodec model in MLX.[^1] EnCodec is used to compress and
+generate audio.
+
+### Setup
+
+Install the requirements:
+
+```
+pip install -r requirements.txt
+```
+
+Optionally install FFmpeg and SciPy for loading and saving audio files,
+respectively.
+
+Install [FFmpeg](https://ffmpeg.org/):
+
+```
+# on macOS using Homebrew (https://brew.sh/)
+brew install ffmpeg
+```
+
+Install SciPy:
+
+```
+pip install scipy
+```
+
+### Example
+
+An example using the model:
+
+```python
+import mlx.core as mx
+from utils import load, load_audio, save_audio
+
+# Load the 48 KHz model and preprocessor.
+model, processor = load("mlx-community/encodec-48khz-float32")
+
+# Load an audio file
+audio = load_audio("path/to/aduio", model.sampling_rate, model.channels)
+
+# Preprocess the audio (this can also be a list of arrays for batched
+# processing).
+feats, mask = processor(audio)
+
+# Encode at the given bandwidth. A lower bandwidth results in more
+# compression but lower reconstruction quality.
+@mx.compile
+def encode(feats, mask):
+    return model.encode(feats, mask, bandwidth=3)
+
+# Decode to reconstruct the audio
+@mx.compile
+def decode(codes, scales, mask):
+    return model.decode(codes, scales, mask)
+
+
+codes, scales = encode(feats, mask)
+reconstructed = decode(codes, scales, mask)
+
+# Trim any padding:
+reconstructed = reconstructed[0, : len(audio)]
+
+# Save the audio as a wave file
+save_audio("reconstructed.wav", reconstructed, model.sampling_rate)
+```
+
+The 24 KHz, 32 KHz, and 48 KHz MLX formatted models are available in the
+[Hugging Face MLX Community](https://huggingface.co/collections/mlx-community/encodec-66e62334038300b07a43b164)
+in several data types.
+
+### Optional
+
+To convert models, use the `convert.py` script. To see the options, run:
+
+```bash
+python convert.py -h
+```
+
+[^1]: Refer to the [arXiv paper](https://arxiv.org/abs/2210.13438) and
+  [code](https://github.com/facebookresearch/encodec) for more details.