diffusers/pipelines/musicldm/pipeline_musicldm.py

# Copyright 2024 The HuggingFace Team. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import inspect
from typing import Any, Callable, Dict, List, Optional, Union

import numpy as np
import torch
from transformers import (
    ClapFeatureExtractor,
    ClapModel,
    ClapTextModelWithProjection,
    RobertaTokenizer,
    RobertaTokenizerFast,
    SpeechT5HifiGan,
)

from ...models import AutoencoderKL, UNet2DConditionModel
from ...schedulers import KarrasDiffusionSchedulers
from ...utils import (
    is_accelerate_available,
    is_accelerate_version,
    is_librosa_available,
    logging,
    replace_example_docstring,
)
from ...utils.torch_utils import randn_tensor
from ..pipeline_utils import AudioPipelineOutput, DiffusionPipeline, StableDiffusionMixin


if is_librosa_available():
    import librosa

logger = logging.get_logger(__name__)  # pylint: disable=invalid-name

EXAMPLE_DOC_STRING = """

    Examples:

        ```py

        >>> from diffusers import MusicLDMPipeline

        >>> import torch

        >>> import scipy



        >>> repo_id = "ucsd-reach/musicldm"

        >>> pipe = MusicLDMPipeline.from_pretrained(repo_id, torch_dtype=torch.float16)

        >>> pipe = pipe.to("cuda")



        >>> prompt = "Techno music with a strong, upbeat tempo and high melodic riffs"

        >>> audio = pipe(prompt, num_inference_steps=10, audio_length_in_s=5.0).audios[0]



        >>> # save the audio sample as a .wav file

        >>> scipy.io.wavfile.write("techno.wav", rate=16000, data=audio)

        ```

"""


class MusicLDMPipeline(DiffusionPipeline, StableDiffusionMixin):
    r"""

    Pipeline for text-to-audio generation using MusicLDM.



    This model inherits from [`DiffusionPipeline`]. Check the superclass documentation for the generic methods

    implemented for all pipelines (downloading, saving, running on a particular device, etc.).



    Args:

        vae ([`AutoencoderKL`]):

            Variational Auto-Encoder (VAE) model to encode and decode images to and from latent representations.

        text_encoder ([`~transformers.ClapModel`]):

            Frozen text-audio embedding model (`ClapTextModel`), specifically the

            [laion/clap-htsat-unfused](https://huggingface.co./laion/clap-htsat-unfused) variant.

        tokenizer ([`PreTrainedTokenizer`]):

            A [`~transformers.RobertaTokenizer`] to tokenize text.

        feature_extractor ([`~transformers.ClapFeatureExtractor`]):

            Feature extractor to compute mel-spectrograms from audio waveforms.

        unet ([`UNet2DConditionModel`]):

            A `UNet2DConditionModel` to denoise the encoded audio latents.

        scheduler ([`SchedulerMixin`]):

            A scheduler to be used in combination with `unet` to denoise the encoded audio latents. Can be one of

            [`DDIMScheduler`], [`LMSDiscreteScheduler`], or [`PNDMScheduler`].

        vocoder ([`~transformers.SpeechT5HifiGan`]):

            Vocoder of class `SpeechT5HifiGan`.

    """

    def __init__(

        self,

        vae: AutoencoderKL,

        text_encoder: Union[ClapTextModelWithProjection, ClapModel],

        tokenizer: Union[RobertaTokenizer, RobertaTokenizerFast],

        feature_extractor: Optional[ClapFeatureExtractor],

        unet: UNet2DConditionModel,

        scheduler: KarrasDiffusionSchedulers,

        vocoder: SpeechT5HifiGan,

    ):
        super().__init__()

        self.register_modules(
            vae=vae,
            text_encoder=text_encoder,
            tokenizer=tokenizer,
            feature_extractor=feature_extractor,
            unet=unet,
            scheduler=scheduler,
            vocoder=vocoder,
        )
        self.vae_scale_factor = 2 ** (len(self.vae.config.block_out_channels) - 1)

    def _encode_prompt(

        self,

        prompt,

        device,

        num_waveforms_per_prompt,

        do_classifier_free_guidance,

        negative_prompt=None,

        prompt_embeds: Optional[torch.FloatTensor] = None,

        negative_prompt_embeds: Optional[torch.FloatTensor] = None,

    ):
        r"""

        Encodes the prompt into text encoder hidden states.



        Args:

            prompt (`str` or `List[str]`, *optional*):

                prompt to be encoded

            device (`torch.device`):

                torch device

            num_waveforms_per_prompt (`int`):

                number of waveforms that should be generated per prompt

            do_classifier_free_guidance (`bool`):

                whether to use classifier free guidance or not

            negative_prompt (`str` or `List[str]`, *optional*):

                The prompt or prompts not to guide the audio generation. If not defined, one has to pass

                `negative_prompt_embeds` instead. Ignored when not using guidance (i.e., ignored if `guidance_scale` is

                less than `1`).

            prompt_embeds (`torch.FloatTensor`, *optional*):

                Pre-generated text embeddings. Can be used to easily tweak text inputs, *e.g.* prompt weighting. If not

                provided, text embeddings will be generated from `prompt` input argument.

            negative_prompt_embeds (`torch.FloatTensor`, *optional*):

                Pre-generated negative text embeddings. Can be used to easily tweak text inputs, *e.g.* prompt

                weighting. If not provided, negative_prompt_embeds will be generated from `negative_prompt` input

                argument.

        """
        if prompt is not None and isinstance(prompt, str):
            batch_size = 1
        elif prompt is not None and isinstance(prompt, list):
            batch_size = len(prompt)
        else:
            batch_size = prompt_embeds.shape[0]

        if prompt_embeds is None:
            text_inputs = self.tokenizer(
                prompt,
                padding="max_length",
                max_length=self.tokenizer.model_max_length,
                truncation=True,
                return_tensors="pt",
            )
            text_input_ids = text_inputs.input_ids
            attention_mask = text_inputs.attention_mask
            untruncated_ids = self.tokenizer(prompt, padding="longest", return_tensors="pt").input_ids

            if untruncated_ids.shape[-1] >= text_input_ids.shape[-1] and not torch.equal(
                text_input_ids, untruncated_ids
            ):
                removed_text = self.tokenizer.batch_decode(
                    untruncated_ids[:, self.tokenizer.model_max_length - 1 : -1]
                )
                logger.warning(
                    "The following part of your input was truncated because CLAP can only handle sequences up to"
                    f" {self.tokenizer.model_max_length} tokens: {removed_text}"
                )

            prompt_embeds = self.text_encoder.get_text_features(
                text_input_ids.to(device),
                attention_mask=attention_mask.to(device),
            )

        prompt_embeds = prompt_embeds.to(dtype=self.text_encoder.text_model.dtype, device=device)

        (
            bs_embed,
            seq_len,
        ) = prompt_embeds.shape
        # duplicate text embeddings for each generation per prompt, using mps friendly method
        prompt_embeds = prompt_embeds.repeat(1, num_waveforms_per_prompt)
        prompt_embeds = prompt_embeds.view(bs_embed * num_waveforms_per_prompt, seq_len)

        # get unconditional embeddings for classifier free guidance
        if do_classifier_free_guidance and negative_prompt_embeds is None:
            uncond_tokens: List[str]
            if negative_prompt is None:
                uncond_tokens = [""] * batch_size
            elif type(prompt) is not type(negative_prompt):
                raise TypeError(
                    f"`negative_prompt` should be the same type to `prompt`, but got {type(negative_prompt)} !="
                    f" {type(prompt)}."
                )
            elif isinstance(negative_prompt, str):
                uncond_tokens = [negative_prompt]
            elif batch_size != len(negative_prompt):
                raise ValueError(
                    f"`negative_prompt`: {negative_prompt} has batch size {len(negative_prompt)}, but `prompt`:"
                    f" {prompt} has batch size {batch_size}. Please make sure that passed `negative_prompt` matches"
                    " the batch size of `prompt`."
                )
            else:
                uncond_tokens = negative_prompt

            max_length = prompt_embeds.shape[1]
            uncond_input = self.tokenizer(
                uncond_tokens,
                padding="max_length",
                max_length=max_length,
                truncation=True,
                return_tensors="pt",
            )

            uncond_input_ids = uncond_input.input_ids.to(device)
            attention_mask = uncond_input.attention_mask.to(device)

            negative_prompt_embeds = self.text_encoder.get_text_features(
                uncond_input_ids,
                attention_mask=attention_mask,
            )

        if do_classifier_free_guidance:
            # duplicate unconditional embeddings for each generation per prompt, using mps friendly method
            seq_len = negative_prompt_embeds.shape[1]

            negative_prompt_embeds = negative_prompt_embeds.to(dtype=self.text_encoder.text_model.dtype, device=device)

            negative_prompt_embeds = negative_prompt_embeds.repeat(1, num_waveforms_per_prompt)
            negative_prompt_embeds = negative_prompt_embeds.view(batch_size * num_waveforms_per_prompt, seq_len)

            # For classifier free guidance, we need to do two forward passes.
            # Here we concatenate the unconditional and text embeddings into a single batch
            # to avoid doing two forward passes
            prompt_embeds = torch.cat([negative_prompt_embeds, prompt_embeds])

        return prompt_embeds

    # Copied from diffusers.pipelines.audioldm.pipeline_audioldm.AudioLDMPipeline.mel_spectrogram_to_waveform
    def mel_spectrogram_to_waveform(self, mel_spectrogram):
        if mel_spectrogram.dim() == 4:
            mel_spectrogram = mel_spectrogram.squeeze(1)

        waveform = self.vocoder(mel_spectrogram)
        # we always cast to float32 as this does not cause significant overhead and is compatible with bfloat16
        waveform = waveform.cpu().float()
        return waveform

    # Copied from diffusers.pipelines.audioldm2.pipeline_audioldm2.AudioLDM2Pipeline.score_waveforms
    def score_waveforms(self, text, audio, num_waveforms_per_prompt, device, dtype):
        if not is_librosa_available():
            logger.info(
                "Automatic scoring of the generated audio waveforms against the input prompt text requires the "
                "`librosa` package to resample the generated waveforms. Returning the audios in the order they were "
                "generated. To enable automatic scoring, install `librosa` with: `pip install librosa`."
            )
            return audio
        inputs = self.tokenizer(text, return_tensors="pt", padding=True)
        resampled_audio = librosa.resample(
            audio.numpy(), orig_sr=self.vocoder.config.sampling_rate, target_sr=self.feature_extractor.sampling_rate
        )
        inputs["input_features"] = self.feature_extractor(
            list(resampled_audio), return_tensors="pt", sampling_rate=self.feature_extractor.sampling_rate
        ).input_features.type(dtype)
        inputs = inputs.to(device)

        # compute the audio-text similarity score using the CLAP model
        logits_per_text = self.text_encoder(**inputs).logits_per_text
        # sort by the highest matching generations per prompt
        indices = torch.argsort(logits_per_text, dim=1, descending=True)[:, :num_waveforms_per_prompt]
        audio = torch.index_select(audio, 0, indices.reshape(-1).cpu())
        return audio

    # Copied from diffusers.pipelines.stable_diffusion.pipeline_stable_diffusion.StableDiffusionPipeline.prepare_extra_step_kwargs
    def prepare_extra_step_kwargs(self, generator, eta):
        # prepare extra kwargs for the scheduler step, since not all schedulers have the same signature
        # eta (η) is only used with the DDIMScheduler, it will be ignored for other schedulers.
        # eta corresponds to η in DDIM paper: https://arxiv.org/abs/2010.02502
        # and should be between [0, 1]

        accepts_eta = "eta" in set(inspect.signature(self.scheduler.step).parameters.keys())
        extra_step_kwargs = {}
        if accepts_eta:
            extra_step_kwargs["eta"] = eta

        # check if the scheduler accepts generator
        accepts_generator = "generator" in set(inspect.signature(self.scheduler.step).parameters.keys())
        if accepts_generator:
            extra_step_kwargs["generator"] = generator
        return extra_step_kwargs

    # Copied from diffusers.pipelines.audioldm.pipeline_audioldm.AudioLDMPipeline.check_inputs
    def check_inputs(

        self,

        prompt,

        audio_length_in_s,

        vocoder_upsample_factor,

        callback_steps,

        negative_prompt=None,

        prompt_embeds=None,

        negative_prompt_embeds=None,

    ):
        min_audio_length_in_s = vocoder_upsample_factor * self.vae_scale_factor
        if audio_length_in_s < min_audio_length_in_s:
            raise ValueError(
                f"`audio_length_in_s` has to be a positive value greater than or equal to {min_audio_length_in_s}, but "
                f"is {audio_length_in_s}."
            )

        if self.vocoder.config.model_in_dim % self.vae_scale_factor != 0:
            raise ValueError(
                f"The number of frequency bins in the vocoder's log-mel spectrogram has to be divisible by the "
                f"VAE scale factor, but got {self.vocoder.config.model_in_dim} bins and a scale factor of "
                f"{self.vae_scale_factor}."
            )

        if (callback_steps is None) or (
            callback_steps is not None and (not isinstance(callback_steps, int) or callback_steps <= 0)
        ):
            raise ValueError(
                f"`callback_steps` has to be a positive integer but is {callback_steps} of type"
                f" {type(callback_steps)}."
            )

        if prompt is not None and prompt_embeds is not None:
            raise ValueError(
                f"Cannot forward both `prompt`: {prompt} and `prompt_embeds`: {prompt_embeds}. Please make sure to"
                " only forward one of the two."
            )
        elif prompt is None and prompt_embeds is None:
            raise ValueError(
                "Provide either `prompt` or `prompt_embeds`. Cannot leave both `prompt` and `prompt_embeds` undefined."
            )
        elif prompt is not None and (not isinstance(prompt, str) and not isinstance(prompt, list)):
            raise ValueError(f"`prompt` has to be of type `str` or `list` but is {type(prompt)}")

        if negative_prompt is not None and negative_prompt_embeds is not None:
            raise ValueError(
                f"Cannot forward both `negative_prompt`: {negative_prompt} and `negative_prompt_embeds`:"
                f" {negative_prompt_embeds}. Please make sure to only forward one of the two."
            )

        if prompt_embeds is not None and negative_prompt_embeds is not None:
            if prompt_embeds.shape != negative_prompt_embeds.shape:
                raise ValueError(
                    "`prompt_embeds` and `negative_prompt_embeds` must have the same shape when passed directly, but"
                    f" got: `prompt_embeds` {prompt_embeds.shape} != `negative_prompt_embeds`"
                    f" {negative_prompt_embeds.shape}."
                )

    # Copied from diffusers.pipelines.audioldm.pipeline_audioldm.AudioLDMPipeline.prepare_latents
    def prepare_latents(self, batch_size, num_channels_latents, height, dtype, device, generator, latents=None):
        shape = (
            batch_size,
            num_channels_latents,
            int(height) // self.vae_scale_factor,
            int(self.vocoder.config.model_in_dim) // self.vae_scale_factor,
        )
        if isinstance(generator, list) and len(generator) != batch_size:
            raise ValueError(
                f"You have passed a list of generators of length {len(generator)}, but requested an effective batch"
                f" size of {batch_size}. Make sure the batch size matches the length of the generators."
            )

        if latents is None:
            latents = randn_tensor(shape, generator=generator, device=device, dtype=dtype)
        else:
            latents = latents.to(device)

        # scale the initial noise by the standard deviation required by the scheduler
        latents = latents * self.scheduler.init_noise_sigma
        return latents

    def enable_model_cpu_offload(self, gpu_id=0):
        r"""

        Offloads all models to CPU using accelerate, reducing memory usage with a low impact on performance. Compared

        to `enable_sequential_cpu_offload`, this method moves one whole model at a time to the GPU when its `forward`

        method is called, and the model remains in GPU until the next model runs. Memory savings are lower than with

        `enable_sequential_cpu_offload`, but performance is much better due to the iterative execution of the `unet`.

        """
        if is_accelerate_available() and is_accelerate_version(">=", "0.17.0.dev0"):
            from accelerate import cpu_offload_with_hook
        else:
            raise ImportError("`enable_model_cpu_offload` requires `accelerate v0.17.0` or higher.")

        device = torch.device(f"cuda:{gpu_id}")

        if self.device.type != "cpu":
            self.to("cpu", silence_dtype_warnings=True)
            torch.cuda.empty_cache()  # otherwise we don't see the memory savings (but they probably exist)

        model_sequence = [
            self.text_encoder.text_model,
            self.text_encoder.text_projection,
            self.unet,
            self.vae,
            self.vocoder,
            self.text_encoder,
        ]

        hook = None
        for cpu_offloaded_model in model_sequence:
            _, hook = cpu_offload_with_hook(cpu_offloaded_model, device, prev_module_hook=hook)

        # We'll offload the last model manually.
        self.final_offload_hook = hook

    @torch.no_grad()
    @replace_example_docstring(EXAMPLE_DOC_STRING)
    def __call__(

        self,

        prompt: Union[str, List[str]] = None,

        audio_length_in_s: Optional[float] = None,

        num_inference_steps: int = 200,

        guidance_scale: float = 2.0,

        negative_prompt: Optional[Union[str, List[str]]] = None,

        num_waveforms_per_prompt: Optional[int] = 1,

        eta: float = 0.0,

        generator: Optional[Union[torch.Generator, List[torch.Generator]]] = None,

        latents: Optional[torch.FloatTensor] = None,

        prompt_embeds: Optional[torch.FloatTensor] = None,

        negative_prompt_embeds: Optional[torch.FloatTensor] = None,

        return_dict: bool = True,

        callback: Optional[Callable[[int, int, torch.FloatTensor], None]] = None,

        callback_steps: Optional[int] = 1,

        cross_attention_kwargs: Optional[Dict[str, Any]] = None,

        output_type: Optional[str] = "np",

    ):
        r"""

        The call function to the pipeline for generation.



        Args:

            prompt (`str` or `List[str]`, *optional*):

                The prompt or prompts to guide audio generation. If not defined, you need to pass `prompt_embeds`.

            audio_length_in_s (`int`, *optional*, defaults to 10.24):

                The length of the generated audio sample in seconds.

            num_inference_steps (`int`, *optional*, defaults to 200):

                The number of denoising steps. More denoising steps usually lead to a higher quality audio at the

                expense of slower inference.

            guidance_scale (`float`, *optional*, defaults to 2.0):

                A higher guidance scale value encourages the model to generate audio that is closely linked to the text

                `prompt` at the expense of lower sound quality. Guidance scale is enabled when `guidance_scale > 1`.

            negative_prompt (`str` or `List[str]`, *optional*):

                The prompt or prompts to guide what to not include in audio generation. If not defined, you need to

                pass `negative_prompt_embeds` instead. Ignored when not using guidance (`guidance_scale < 1`).

            num_waveforms_per_prompt (`int`, *optional*, defaults to 1):

                The number of waveforms to generate per prompt. If `num_waveforms_per_prompt > 1`, the text encoding

                model is a joint text-audio model ([`~transformers.ClapModel`]), and the tokenizer is a

                `[~transformers.ClapProcessor]`, then automatic scoring will be performed between the generated outputs

                and the input text. This scoring ranks the generated waveforms based on their cosine similarity to text

                input in the joint text-audio embedding space.

            eta (`float`, *optional*, defaults to 0.0):

                Corresponds to parameter eta (η) from the [DDIM](https://arxiv.org/abs/2010.02502) paper. Only applies

                to the [`~schedulers.DDIMScheduler`], and is ignored in other schedulers.

            generator (`torch.Generator` or `List[torch.Generator]`, *optional*):

                A [`torch.Generator`](https://pytorch.org/docs/stable/generated/torch.Generator.html) to make

                generation deterministic.

            latents (`torch.FloatTensor`, *optional*):

                Pre-generated noisy latents sampled from a Gaussian distribution, to be used as inputs for image

                generation. Can be used to tweak the same generation with different prompts. If not provided, a latents

                tensor is generated by sampling using the supplied random `generator`.

            prompt_embeds (`torch.FloatTensor`, *optional*):

                Pre-generated text embeddings. Can be used to easily tweak text inputs (prompt weighting). If not

                provided, text embeddings are generated from the `prompt` input argument.

            negative_prompt_embeds (`torch.FloatTensor`, *optional*):

                Pre-generated negative text embeddings. Can be used to easily tweak text inputs (prompt weighting). If

                not provided, `negative_prompt_embeds` are generated from the `negative_prompt` input argument.

            return_dict (`bool`, *optional*, defaults to `True`):

                Whether or not to return a [`~pipelines.AudioPipelineOutput`] instead of a plain tuple.

            callback (`Callable`, *optional*):

                A function that calls every `callback_steps` steps during inference. The function is called with the

                following arguments: `callback(step: int, timestep: int, latents: torch.FloatTensor)`.

            callback_steps (`int`, *optional*, defaults to 1):

                The frequency at which the `callback` function is called. If not specified, the callback is called at

                every step.

            cross_attention_kwargs (`dict`, *optional*):

                A kwargs dictionary that if specified is passed along to the [`AttentionProcessor`] as defined in

                [`self.processor`](https://github.com/huggingface/diffusers/blob/main/src/diffusers/models/attention_processor.py).

            output_type (`str`, *optional*, defaults to `"np"`):

                The output format of the generated audio. Choose between `"np"` to return a NumPy `np.ndarray` or

                `"pt"` to return a PyTorch `torch.Tensor` object. Set to `"latent"` to return the latent diffusion

                model (LDM) output.



        Examples:



        Returns:

            [`~pipelines.AudioPipelineOutput`] or `tuple`:

                If `return_dict` is `True`, [`~pipelines.AudioPipelineOutput`] is returned, otherwise a `tuple` is

                returned where the first element is a list with the generated audio.

        """
        # 0. Convert audio input length from seconds to spectrogram height
        vocoder_upsample_factor = np.prod(self.vocoder.config.upsample_rates) / self.vocoder.config.sampling_rate

        if audio_length_in_s is None:
            audio_length_in_s = self.unet.config.sample_size * self.vae_scale_factor * vocoder_upsample_factor

        height = int(audio_length_in_s / vocoder_upsample_factor)

        original_waveform_length = int(audio_length_in_s * self.vocoder.config.sampling_rate)
        if height % self.vae_scale_factor != 0:
            height = int(np.ceil(height / self.vae_scale_factor)) * self.vae_scale_factor
            logger.info(
                f"Audio length in seconds {audio_length_in_s} is increased to {height * vocoder_upsample_factor} "
                f"so that it can be handled by the model. It will be cut to {audio_length_in_s} after the "
                f"denoising process."
            )

        # 1. Check inputs. Raise error if not correct
        self.check_inputs(
            prompt,
            audio_length_in_s,
            vocoder_upsample_factor,
            callback_steps,
            negative_prompt,
            prompt_embeds,
            negative_prompt_embeds,
        )

        # 2. Define call parameters
        if prompt is not None and isinstance(prompt, str):
            batch_size = 1
        elif prompt is not None and isinstance(prompt, list):
            batch_size = len(prompt)
        else:
            batch_size = prompt_embeds.shape[0]

        device = self._execution_device
        # here `guidance_scale` is defined analog to the guidance weight `w` of equation (2)
        # of the Imagen paper: https://arxiv.org/pdf/2205.11487.pdf . `guidance_scale = 1`
        # corresponds to doing no classifier free guidance.
        do_classifier_free_guidance = guidance_scale > 1.0

        # 3. Encode input prompt
        prompt_embeds = self._encode_prompt(
            prompt,
            device,
            num_waveforms_per_prompt,
            do_classifier_free_guidance,
            negative_prompt,
            prompt_embeds=prompt_embeds,
            negative_prompt_embeds=negative_prompt_embeds,
        )

        # 4. Prepare timesteps
        self.scheduler.set_timesteps(num_inference_steps, device=device)
        timesteps = self.scheduler.timesteps

        # 5. Prepare latent variables
        num_channels_latents = self.unet.config.in_channels
        latents = self.prepare_latents(
            batch_size * num_waveforms_per_prompt,
            num_channels_latents,
            height,
            prompt_embeds.dtype,
            device,
            generator,
            latents,
        )

        # 6. Prepare extra step kwargs
        extra_step_kwargs = self.prepare_extra_step_kwargs(generator, eta)

        # 7. Denoising loop
        num_warmup_steps = len(timesteps) - num_inference_steps * self.scheduler.order
        with self.progress_bar(total=num_inference_steps) as progress_bar:
            for i, t in enumerate(timesteps):
                # expand the latents if we are doing classifier free guidance
                latent_model_input = torch.cat([latents] * 2) if do_classifier_free_guidance else latents
                latent_model_input = self.scheduler.scale_model_input(latent_model_input, t)

                # predict the noise residual
                noise_pred = self.unet(
                    latent_model_input,
                    t,
                    encoder_hidden_states=None,
                    class_labels=prompt_embeds,
                    cross_attention_kwargs=cross_attention_kwargs,
                    return_dict=False,
                )[0]

                # perform guidance
                if do_classifier_free_guidance:
                    noise_pred_uncond, noise_pred_text = noise_pred.chunk(2)
                    noise_pred = noise_pred_uncond + guidance_scale * (noise_pred_text - noise_pred_uncond)

                # compute the previous noisy sample x_t -> x_t-1
                latents = self.scheduler.step(noise_pred, t, latents, **extra_step_kwargs).prev_sample

                # call the callback, if provided
                if i == len(timesteps) - 1 or ((i + 1) > num_warmup_steps and (i + 1) % self.scheduler.order == 0):
                    progress_bar.update()
                    if callback is not None and i % callback_steps == 0:
                        step_idx = i // getattr(self.scheduler, "order", 1)
                        callback(step_idx, t, latents)

        self.maybe_free_model_hooks()

        # 8. Post-processing
        if not output_type == "latent":
            latents = 1 / self.vae.config.scaling_factor * latents
            mel_spectrogram = self.vae.decode(latents).sample
        else:
            return AudioPipelineOutput(audios=latents)

        audio = self.mel_spectrogram_to_waveform(mel_spectrogram)

        audio = audio[:, :original_waveform_length]

        # 9. Automatic scoring
        if num_waveforms_per_prompt > 1 and prompt is not None:
            audio = self.score_waveforms(
                text=prompt,
                audio=audio,
                num_waveforms_per_prompt=num_waveforms_per_prompt,
                device=device,
                dtype=prompt_embeds.dtype,
            )

        if output_type == "np":
            audio = audio.numpy()

        if not return_dict:
            return (audio,)

        return AudioPipelineOutput(audios=audio)