Add training and inference source code

2ea2835 verified 20 days ago

16.1 kB

from typing import Tuple
from einops import rearrange
from torch import nn
import torch.distributed as dist
import torch

from pipeline import SelfForcingTrainingPipeline
from utils.loss import get_denoising_loss
from utils.wan_wrapper import WanDiffusionWrapper, WanTextEncoder, WanVAEWrapper


class BaseModel(nn.Module):
    def __init__(self, args, device):
        super().__init__()
        self._initialize_models(args, device)

        self.device = device
        self.args = args
        self.dtype = torch.bfloat16 if args.mixed_precision else torch.float32
        if hasattr(args, "denoising_step_list"):
            self.denoising_step_list = torch.tensor(args.denoising_step_list, dtype=torch.long)
            if args.warp_denoising_step:
                timesteps = torch.cat((self.scheduler.timesteps.cpu(), torch.tensor([0], dtype=torch.float32)))
                self.denoising_step_list = timesteps[1000 - self.denoising_step_list]

    def _initialize_models(self, args, device):
        self.real_model_name = getattr(args, "real_name", "Wan2.1-T2V-1.3B")
        self.fake_model_name = getattr(args, "fake_name", "Wan2.1-T2V-1.3B")

        gen_kwargs = dict(getattr(args, "model_kwargs", {}))
        if getattr(args, "attention_type", "softmax") != "softmax":
            raise ValueError("Only causal softmax attention is supported")
        gen_kwargs.setdefault("attention_type", "softmax")
        self.generator = WanDiffusionWrapper(
            **gen_kwargs, is_causal=bool(getattr(args, "causal", True)))

        self.generator.model.requires_grad_(True)

        self.uses_score_models = bool(
            getattr(args, "uses_score_models", getattr(args, "distribution_loss", None) != "fd")
        )
        self.uses_real_score = bool(getattr(args, "uses_real_score", self.uses_score_models))
        self.uses_fake_score = bool(getattr(args, "uses_fake_score", self.uses_score_models))
        if self.uses_real_score:
            self.real_score = WanDiffusionWrapper(model_name=self.real_model_name, is_causal=False)
            self.real_score.model.requires_grad_(False)
        else:
            self.real_score = None
        if self.uses_fake_score:
            self.fake_score = WanDiffusionWrapper(model_name=self.fake_model_name, is_causal=False)
            self.fake_score.model.requires_grad_(True)
        else:
            self.fake_score = None

        # Construct the frozen 5.7B T5 encoder directly in the training dtype.
        # Building four temporary fp32 copies can otherwise exceed host memory
        # before FSDP gets a chance to shard them.
        text_dtype = (
            torch.bfloat16 if bool(getattr(args, "mixed_precision", False))
            else torch.float32
        )
        self.text_encoder = WanTextEncoder(dtype=text_dtype)
        self.text_encoder.requires_grad_(False)

        self.vae = WanVAEWrapper()
        self.vae.requires_grad_(False)

        self.scheduler = self.generator.get_scheduler()
        self.scheduler.timesteps = self.scheduler.timesteps.to(device)

    def _get_timestep(
            self,
            min_timestep: int,
            max_timestep: int,
            batch_size: int,
            num_frame: int,
            num_frame_per_block: int,
            uniform_timestep: bool = False
    ) -> torch.Tensor:
        """
        Randomly generate a timestep tensor based on the generator's task type. It uniformly samples a timestep
        from the range [min_timestep, max_timestep], and returns a tensor of shape [batch_size, num_frame].
        - If uniform_timestep, it will use the same timestep for all frames.
        - If not uniform_timestep, it will use a different timestep for each block.
        """
        if uniform_timestep:
            timestep = torch.randint(
                min_timestep,
                max_timestep,
                [batch_size, 1],
                device=self.device,
                dtype=torch.long
            ).repeat(1, num_frame)
            return timestep
        else:
            timestep = torch.randint(
                min_timestep,
                max_timestep,
                [batch_size, num_frame],
                device=self.device,
                dtype=torch.long
            )
            # make the noise level the same within every block
            if self.independent_first_frame:
                # the first frame is always kept the same
                timestep_from_second = timestep[:, 1:]
                timestep_from_second = timestep_from_second.reshape(
                    timestep_from_second.shape[0], -1, num_frame_per_block)
                timestep_from_second[:, :, 1:] = timestep_from_second[:, :, 0:1]
                timestep_from_second = timestep_from_second.reshape(
                    timestep_from_second.shape[0], -1)
                timestep = torch.cat([timestep[:, 0:1], timestep_from_second], dim=1)
            else:
                timestep = timestep.reshape(
                    timestep.shape[0], -1, num_frame_per_block)
                timestep[:, :, 1:] = timestep[:, :, 0:1]
                timestep = timestep.reshape(timestep.shape[0], -1)
            return timestep


class SelfForcingModel(BaseModel):
    def __init__(self, args, device):
        super().__init__(args, device)
        self.denoising_loss_func = get_denoising_loss(args.denoising_loss_type)()

    def _sample_generator_input_descriptor(
        self,
        image_or_video_shape,
        initial_latent: torch.Tensor = None,
    ) -> dict:
        """Explicitly sample `_run_generator`'s block count and initial noise.
        The returned descriptor is reusable: passing it back to
        ``_run_generator`` avoids consulting the ambient RNG for those direct
        inputs.  A caller replaying the full rollout must additionally capture
        the post-sampling RNG state used by stochastic pipeline internals.
        """
        if self.args.i2v:
            noise_shape = [
                image_or_video_shape[0],
                image_or_video_shape[1] - 1,
                *image_or_video_shape[2:],
            ]
        else:
            noise_shape = list(image_or_video_shape)

        min_num_frames = 20 if self.args.independent_first_frame else 21
        max_num_frames = (
            self.num_training_frames - 1
            if self.args.independent_first_frame
            else self.num_training_frames
        )
        if max_num_frames % self.num_frame_per_block != 0:
            raise ValueError(
                "num_training_frames is not divisible by "
                "num_frame_per_block")
        if min_num_frames % self.num_frame_per_block != 0:
            raise ValueError(
                "minimum generated frames is not divisible by "
                "num_frame_per_block")
        max_num_blocks = max_num_frames // self.num_frame_per_block
        min_num_blocks = min_num_frames // self.num_frame_per_block
        block_count = torch.randint(
            min_num_blocks,
            max_num_blocks + 1,
            (1,),
            device=self.device,
        )
        if dist.is_available() and dist.is_initialized():
            dist.broadcast(block_count, src=0)
        num_generated_blocks = int(block_count.item())
        num_generated_frames = (
            num_generated_blocks * self.num_frame_per_block)
        if self.args.independent_first_frame and initial_latent is None:
            num_generated_frames += 1
        noise_shape[1] = num_generated_frames
        return {
            "version": 1,
            "num_generated_blocks": num_generated_blocks,
            "noise": torch.randn(
                noise_shape, device=self.device, dtype=self.dtype),
        }

    def _run_generator(
        self,
        image_or_video_shape,
        conditional_dict: dict,
        initial_latent: torch.tensor = None,
        generation_descriptor: dict = None,
    ) -> Tuple[torch.Tensor, torch.Tensor]:
        """
        Optionally simulate the generator's input from noise using backward simulation
        and then run the generator for one-step.
        Input:
            - image_or_video_shape: a list containing the shape of the image or video [B, F, C, H, W].
            - conditional_dict: a dictionary containing the conditional information (e.g. text embeddings, image embeddings).
            - unconditional_dict: a dictionary containing the unconditional information (e.g. null/negative text embeddings, null/negative image embeddings).
            - clean_latent: a tensor containing the clean latents [B, F, C, H, W]. Need to be passed when no backward simulation is used.
            - initial_latent: a tensor containing the initial latents [B, F, C, H, W].
        Output:
            - pred_image: a tensor with shape [B, F, C, H, W].
            - denoised_timestep: an integer
        """
        # Step 1: Sample noise and backward simulate the generator's input
        assert getattr(self.args, "backward_simulation", True), "Backward simulation needs to be enabled"
        if initial_latent is not None:
            conditional_dict["initial_latent"] = initial_latent
        # During training, the number of generated frames should be uniformly sampled from
        # [21, self.num_training_frames], but still being a multiple of self.num_frame_per_block
        min_num_frames = 20 if self.args.independent_first_frame else 21
        max_num_frames = self.num_training_frames - 1 if self.args.independent_first_frame else self.num_training_frames
        assert max_num_frames % self.num_frame_per_block == 0
        assert min_num_frames % self.num_frame_per_block == 0
        max_num_blocks = max_num_frames // self.num_frame_per_block
        min_num_blocks = min_num_frames // self.num_frame_per_block
        if generation_descriptor is None:
            generation_descriptor = (
                self._sample_generator_input_descriptor(
                    image_or_video_shape,
                    initial_latent=initial_latent,
                )
            )
        if (
            not isinstance(generation_descriptor, dict)
            or set(generation_descriptor)
            != {"version", "num_generated_blocks", "noise"}
            or int(generation_descriptor["version"]) != 1
        ):
            raise ValueError("invalid explicit generator input descriptor")
        num_generated_blocks = int(
            generation_descriptor["num_generated_blocks"])
        if not min_num_blocks <= num_generated_blocks <= max_num_blocks:
            raise ValueError(
                "generator descriptor block count is outside the configured "
                f"range [{min_num_blocks}, {max_num_blocks}]")
        if dist.is_available() and dist.is_initialized():
            block_min = torch.tensor(
                num_generated_blocks, device=self.device, dtype=torch.long)
            block_max = block_min.clone()
            dist.all_reduce(block_min, op=dist.ReduceOp.MIN)
            dist.all_reduce(block_max, op=dist.ReduceOp.MAX)
            if int(block_min.item()) != int(block_max.item()):
                raise ValueError(
                    "generator descriptor block count differs across ranks")
        num_generated_frames = num_generated_blocks * self.num_frame_per_block
        if self.args.independent_first_frame and initial_latent is None:
            num_generated_frames += 1
            min_num_frames += 1
        expected_noise_shape = list(image_or_video_shape)
        if self.args.i2v:
            expected_noise_shape[1] -= 1
        expected_noise_shape[1] = num_generated_frames
        generation_noise = generation_descriptor["noise"]
        expected_device = (
            torch.device("cuda", int(self.device))
            if isinstance(self.device, int)
            else torch.device(self.device)
        )
        if (
            not isinstance(generation_noise, torch.Tensor)
            or tuple(generation_noise.shape) != tuple(expected_noise_shape)
            or generation_noise.device != expected_device
            or generation_noise.dtype != self.dtype
            or not bool(torch.isfinite(generation_noise).all().item())
        ):
            raise ValueError(
                "generator descriptor noise is incompatible with the "
                f"expected {tuple(expected_noise_shape)} {self.dtype} on "
                f"{expected_device}")

        pred_image_or_video, denoised_timestep_from, denoised_timestep_to = self._consistency_backward_simulation(
            noise=generation_noise,
            **conditional_dict,
        )
        # Slice last 21 frames
        if pred_image_or_video.shape[1] > 21:
            with torch.no_grad():
                # Reencode to get image latent
                latent_to_decode = pred_image_or_video[:, :-20, ...]
                # Deccode to video
                pixels = self.vae.decode_to_pixel(latent_to_decode)
                frame = pixels[:, -1:, ...].to(self.dtype)
                frame = rearrange(frame, "b t c h w -> b c t h w")
                # Encode frame to get image latent
                image_latent = self.vae.encode_to_latent(frame).to(self.dtype)
            pred_image_or_video_last_21 = torch.cat([image_latent, pred_image_or_video[:, -20:, ...]], dim=1)
        else:
            pred_image_or_video_last_21 = pred_image_or_video

        if num_generated_frames != min_num_frames:
            # Currently, we do not use gradient for the first chunk, since it contains image latents
            gradient_mask = torch.ones_like(pred_image_or_video_last_21, dtype=torch.bool)
            if self.args.independent_first_frame:
                gradient_mask[:, :1] = False
            else:
                gradient_mask[:, :self.num_frame_per_block] = False
        else:
            gradient_mask = None

        pred_image_or_video_last_21 = pred_image_or_video_last_21.to(self.dtype)
        return pred_image_or_video_last_21, gradient_mask, denoised_timestep_from, denoised_timestep_to

    def _consistency_backward_simulation(
        self,
        noise: torch.Tensor,
        **conditional_dict: dict
    ) -> torch.Tensor:
        """
        Simulate the generator's input from noise to avoid training/inference mismatch.
        See Sec 4.5 of the DMD2 paper (https://arxiv.org/abs/2405.14867) for details.
        Here we use the consistency sampler (https://arxiv.org/abs/2303.01469)
        Input:
            - noise: a tensor sampled from N(0, 1) with shape [B, F, C, H, W] where the number of frame is 1 for images.
            - conditional_dict: a dictionary containing the conditional information (e.g. text embeddings, image embeddings).
        Output:
            - output: a tensor with shape [B, T, F, C, H, W].
            T is the total number of timesteps. output[0] is a pure noise and output[i] and i>0
            represents the x0 prediction at each timestep.
        """
        if self.inference_pipeline is None:
            self._initialize_inference_pipeline()

        return self.inference_pipeline.inference_with_trajectory(
            noise=noise, **conditional_dict
        )

    def _initialize_inference_pipeline(self):
        """
        Lazy initialize the inference pipeline during the first backward simulation run.
        Here we encapsulate the inference code with a model-dependent outside function.
        We pass our FSDP-wrapped modules into the pipeline to save memory.
        """
        self.inference_pipeline = SelfForcingTrainingPipeline(
            denoising_step_list=self.denoising_step_list,
            scheduler=self.scheduler,
            generator=self.generator,
            num_frame_per_block=self.num_frame_per_block,
            independent_first_frame=self.args.independent_first_frame,
            same_step_across_blocks=self.args.same_step_across_blocks,
            last_step_only=self.args.last_step_only,
            num_max_frames=self.num_training_frames,
            context_noise=self.args.context_noise
        )

	from typing import Tuple
	from einops import rearrange
	from torch import nn
	import torch.distributed as dist
	import torch

	from pipeline import SelfForcingTrainingPipeline
	from utils.loss import get_denoising_loss
	from utils.wan_wrapper import WanDiffusionWrapper, WanTextEncoder, WanVAEWrapper


	class BaseModel(nn.Module):
	def __init__(self, args, device):
	super().__init__()
	self._initialize_models(args, device)

	self.device = device
	self.args = args
	self.dtype = torch.bfloat16 if args.mixed_precision else torch.float32
	if hasattr(args, "denoising_step_list"):
	self.denoising_step_list = torch.tensor(args.denoising_step_list, dtype=torch.long)
	if args.warp_denoising_step:
	timesteps = torch.cat((self.scheduler.timesteps.cpu(), torch.tensor([0], dtype=torch.float32)))
	self.denoising_step_list = timesteps[1000 - self.denoising_step_list]

	def _initialize_models(self, args, device):
	self.real_model_name = getattr(args, "real_name", "Wan2.1-T2V-1.3B")
	self.fake_model_name = getattr(args, "fake_name", "Wan2.1-T2V-1.3B")

	gen_kwargs = dict(getattr(args, "model_kwargs", {}))
	if getattr(args, "attention_type", "softmax") != "softmax":
	raise ValueError("Only causal softmax attention is supported")
	gen_kwargs.setdefault("attention_type", "softmax")
	self.generator = WanDiffusionWrapper(
	**gen_kwargs, is_causal=bool(getattr(args, "causal", True)))

	self.generator.model.requires_grad_(True)

	self.uses_score_models = bool(
	getattr(args, "uses_score_models", getattr(args, "distribution_loss", None) != "fd")
	)
	self.uses_real_score = bool(getattr(args, "uses_real_score", self.uses_score_models))
	self.uses_fake_score = bool(getattr(args, "uses_fake_score", self.uses_score_models))
	if self.uses_real_score:
	self.real_score = WanDiffusionWrapper(model_name=self.real_model_name, is_causal=False)
	self.real_score.model.requires_grad_(False)
	else:
	self.real_score = None
	if self.uses_fake_score:
	self.fake_score = WanDiffusionWrapper(model_name=self.fake_model_name, is_causal=False)
	self.fake_score.model.requires_grad_(True)
	else:
	self.fake_score = None

	# Construct the frozen 5.7B T5 encoder directly in the training dtype.
	# Building four temporary fp32 copies can otherwise exceed host memory
	# before FSDP gets a chance to shard them.
	text_dtype = (
	torch.bfloat16 if bool(getattr(args, "mixed_precision", False))
	else torch.float32
	)
	self.text_encoder = WanTextEncoder(dtype=text_dtype)
	self.text_encoder.requires_grad_(False)

	self.vae = WanVAEWrapper()
	self.vae.requires_grad_(False)

	self.scheduler = self.generator.get_scheduler()
	self.scheduler.timesteps = self.scheduler.timesteps.to(device)

	def _get_timestep(
	self,
	min_timestep: int,
	max_timestep: int,
	batch_size: int,
	num_frame: int,
	num_frame_per_block: int,
	uniform_timestep: bool = False
	) -> torch.Tensor:
	"""
	Randomly generate a timestep tensor based on the generator's task type. It uniformly samples a timestep
	from the range [min_timestep, max_timestep], and returns a tensor of shape [batch_size, num_frame].
	- If uniform_timestep, it will use the same timestep for all frames.
	- If not uniform_timestep, it will use a different timestep for each block.
	"""
	if uniform_timestep:
	timestep = torch.randint(
	min_timestep,
	max_timestep,
	[batch_size, 1],
	device=self.device,
	dtype=torch.long
	).repeat(1, num_frame)
	return timestep
	else:
	timestep = torch.randint(
	min_timestep,
	max_timestep,
	[batch_size, num_frame],
	device=self.device,
	dtype=torch.long
	)
	# make the noise level the same within every block
	if self.independent_first_frame:
	# the first frame is always kept the same
	timestep_from_second = timestep[:, 1:]
	timestep_from_second = timestep_from_second.reshape(
	timestep_from_second.shape[0], -1, num_frame_per_block)
	timestep_from_second[:, :, 1:] = timestep_from_second[:, :, 0:1]
	timestep_from_second = timestep_from_second.reshape(
	timestep_from_second.shape[0], -1)
	timestep = torch.cat([timestep[:, 0:1], timestep_from_second], dim=1)
	else:
	timestep = timestep.reshape(
	timestep.shape[0], -1, num_frame_per_block)
	timestep[:, :, 1:] = timestep[:, :, 0:1]
	timestep = timestep.reshape(timestep.shape[0], -1)
	return timestep


	class SelfForcingModel(BaseModel):
	def __init__(self, args, device):
	super().__init__(args, device)
	self.denoising_loss_func = get_denoising_loss(args.denoising_loss_type)()

	def _sample_generator_input_descriptor(
	self,
	image_or_video_shape,
	initial_latent: torch.Tensor = None,
	) -> dict:
	"""Explicitly sample `_run_generator`'s block count and initial noise.

	The returned descriptor is reusable: passing it back to
	``_run_generator`` avoids consulting the ambient RNG for those direct
	inputs. A caller replaying the full rollout must additionally capture
	the post-sampling RNG state used by stochastic pipeline internals.
	"""
	if self.args.i2v:
	noise_shape = [
	image_or_video_shape[0],
	image_or_video_shape[1] - 1,
	*image_or_video_shape[2:],
	]
	else:
	noise_shape = list(image_or_video_shape)

	min_num_frames = 20 if self.args.independent_first_frame else 21
	max_num_frames = (
	self.num_training_frames - 1
	if self.args.independent_first_frame
	else self.num_training_frames
	)
	if max_num_frames % self.num_frame_per_block != 0:
	raise ValueError(
	"num_training_frames is not divisible by "
	"num_frame_per_block")
	if min_num_frames % self.num_frame_per_block != 0:
	raise ValueError(
	"minimum generated frames is not divisible by "
	"num_frame_per_block")
	max_num_blocks = max_num_frames // self.num_frame_per_block
	min_num_blocks = min_num_frames // self.num_frame_per_block
	block_count = torch.randint(
	min_num_blocks,
	max_num_blocks + 1,
	(1,),
	device=self.device,
	)
	if dist.is_available() and dist.is_initialized():
	dist.broadcast(block_count, src=0)
	num_generated_blocks = int(block_count.item())
	num_generated_frames = (
	num_generated_blocks * self.num_frame_per_block)
	if self.args.independent_first_frame and initial_latent is None:
	num_generated_frames += 1
	noise_shape[1] = num_generated_frames
	return {
	"version": 1,
	"num_generated_blocks": num_generated_blocks,
	"noise": torch.randn(
	noise_shape, device=self.device, dtype=self.dtype),
	}

	def _run_generator(
	self,
	image_or_video_shape,
	conditional_dict: dict,
	initial_latent: torch.tensor = None,
	generation_descriptor: dict = None,
	) -> Tuple[torch.Tensor, torch.Tensor]:
	"""
	Optionally simulate the generator's input from noise using backward simulation
	and then run the generator for one-step.
	Input:
	- image_or_video_shape: a list containing the shape of the image or video [B, F, C, H, W].
	- conditional_dict: a dictionary containing the conditional information (e.g. text embeddings, image embeddings).
	- unconditional_dict: a dictionary containing the unconditional information (e.g. null/negative text embeddings, null/negative image embeddings).
	- clean_latent: a tensor containing the clean latents [B, F, C, H, W]. Need to be passed when no backward simulation is used.
	- initial_latent: a tensor containing the initial latents [B, F, C, H, W].
	Output:
	- pred_image: a tensor with shape [B, F, C, H, W].
	- denoised_timestep: an integer
	"""
	# Step 1: Sample noise and backward simulate the generator's input
	assert getattr(self.args, "backward_simulation", True), "Backward simulation needs to be enabled"
	if initial_latent is not None:
	conditional_dict["initial_latent"] = initial_latent
	# During training, the number of generated frames should be uniformly sampled from
	# [21, self.num_training_frames], but still being a multiple of self.num_frame_per_block
	min_num_frames = 20 if self.args.independent_first_frame else 21
	max_num_frames = self.num_training_frames - 1 if self.args.independent_first_frame else self.num_training_frames
	assert max_num_frames % self.num_frame_per_block == 0
	assert min_num_frames % self.num_frame_per_block == 0
	max_num_blocks = max_num_frames // self.num_frame_per_block
	min_num_blocks = min_num_frames // self.num_frame_per_block
	if generation_descriptor is None:
	generation_descriptor = (
	self._sample_generator_input_descriptor(
	image_or_video_shape,
	initial_latent=initial_latent,
	)
	)
	if (
	not isinstance(generation_descriptor, dict)
	or set(generation_descriptor)
	!= {"version", "num_generated_blocks", "noise"}
	or int(generation_descriptor["version"]) != 1
	):
	raise ValueError("invalid explicit generator input descriptor")
	num_generated_blocks = int(
	generation_descriptor["num_generated_blocks"])
	if not min_num_blocks <= num_generated_blocks <= max_num_blocks:
	raise ValueError(
	"generator descriptor block count is outside the configured "
	f"range [{min_num_blocks}, {max_num_blocks}]")
	if dist.is_available() and dist.is_initialized():
	block_min = torch.tensor(
	num_generated_blocks, device=self.device, dtype=torch.long)
	block_max = block_min.clone()
	dist.all_reduce(block_min, op=dist.ReduceOp.MIN)
	dist.all_reduce(block_max, op=dist.ReduceOp.MAX)
	if int(block_min.item()) != int(block_max.item()):
	raise ValueError(
	"generator descriptor block count differs across ranks")
	num_generated_frames = num_generated_blocks * self.num_frame_per_block
	if self.args.independent_first_frame and initial_latent is None:
	num_generated_frames += 1
	min_num_frames += 1
	expected_noise_shape = list(image_or_video_shape)
	if self.args.i2v:
	expected_noise_shape[1] -= 1
	expected_noise_shape[1] = num_generated_frames
	generation_noise = generation_descriptor["noise"]
	expected_device = (
	torch.device("cuda", int(self.device))
	if isinstance(self.device, int)
	else torch.device(self.device)
	)
	if (
	not isinstance(generation_noise, torch.Tensor)
	or tuple(generation_noise.shape) != tuple(expected_noise_shape)
	or generation_noise.device != expected_device
	or generation_noise.dtype != self.dtype
	or not bool(torch.isfinite(generation_noise).all().item())
	):
	raise ValueError(
	"generator descriptor noise is incompatible with the "
	f"expected {tuple(expected_noise_shape)} {self.dtype} on "
	f"{expected_device}")

	pred_image_or_video, denoised_timestep_from, denoised_timestep_to = self._consistency_backward_simulation(
	noise=generation_noise,
	**conditional_dict,
	)
	# Slice last 21 frames
	if pred_image_or_video.shape[1] > 21:
	with torch.no_grad():
	# Reencode to get image latent
	latent_to_decode = pred_image_or_video[:, :-20, ...]
	# Deccode to video
	pixels = self.vae.decode_to_pixel(latent_to_decode)
	frame = pixels[:, -1:, ...].to(self.dtype)
	frame = rearrange(frame, "b t c h w -> b c t h w")
	# Encode frame to get image latent
	image_latent = self.vae.encode_to_latent(frame).to(self.dtype)
	pred_image_or_video_last_21 = torch.cat([image_latent, pred_image_or_video[:, -20:, ...]], dim=1)
	else:
	pred_image_or_video_last_21 = pred_image_or_video

	if num_generated_frames != min_num_frames:
	# Currently, we do not use gradient for the first chunk, since it contains image latents
	gradient_mask = torch.ones_like(pred_image_or_video_last_21, dtype=torch.bool)
	if self.args.independent_first_frame:
	gradient_mask[:, :1] = False
	else:
	gradient_mask[:, :self.num_frame_per_block] = False
	else:
	gradient_mask = None

	pred_image_or_video_last_21 = pred_image_or_video_last_21.to(self.dtype)
	return pred_image_or_video_last_21, gradient_mask, denoised_timestep_from, denoised_timestep_to

	def _consistency_backward_simulation(
	self,
	noise: torch.Tensor,
	**conditional_dict: dict
	) -> torch.Tensor:
	"""
	Simulate the generator's input from noise to avoid training/inference mismatch.
	See Sec 4.5 of the DMD2 paper (https://arxiv.org/abs/2405.14867) for details.
	Here we use the consistency sampler (https://arxiv.org/abs/2303.01469)
	Input:
	- noise: a tensor sampled from N(0, 1) with shape [B, F, C, H, W] where the number of frame is 1 for images.
	- conditional_dict: a dictionary containing the conditional information (e.g. text embeddings, image embeddings).
	Output:
	- output: a tensor with shape [B, T, F, C, H, W].
	T is the total number of timesteps. output[0] is a pure noise and output[i] and i>0
	represents the x0 prediction at each timestep.
	"""
	if self.inference_pipeline is None:
	self._initialize_inference_pipeline()

	return self.inference_pipeline.inference_with_trajectory(
	noise=noise, **conditional_dict
	)

	def _initialize_inference_pipeline(self):
	"""
	Lazy initialize the inference pipeline during the first backward simulation run.
	Here we encapsulate the inference code with a model-dependent outside function.
	We pass our FSDP-wrapped modules into the pipeline to save memory.
	"""
	self.inference_pipeline = SelfForcingTrainingPipeline(
	denoising_step_list=self.denoising_step_list,
	scheduler=self.scheduler,
	generator=self.generator,
	num_frame_per_block=self.num_frame_per_block,
	independent_first_frame=self.args.independent_first_frame,
	same_step_across_blocks=self.args.same_step_across_blocks,
	last_step_only=self.args.last_step_only,
	num_max_frames=self.num_training_frames,
	context_noise=self.args.context_noise
	)