add code

src/diffusers/pipelines/stable_video_diffusion/pipeline_stable_video_diffusion.py

@@ -309,6 +309,7 @@ class StableVideoDiffusionPipeline(DiffusionPipeline):
         num_inference_steps: int = 25,
         min_guidance_scale: float = 1.0,
         max_guidance_scale: float = 3.0,
+        rec_guidance_scale: float = 1.0,
         fps: int = 7,
         motion_bucket_id: int = 127,
         noise_aug_strength: int = 0.02,
@@ -535,6 +536,136 @@ class StableVideoDiffusionPipeline(DiffusionPipeline):
         else:
             frames = latents
         
+        
+        # 3. Encode input image
+        next_image = frames[0][-1]
+        next_image_embeddings = self._encode_image(next_image, device, num_videos_per_prompt, self.do_classifier_free_guidance)
+
+        # 4. Encode input image using VAE
+        next_image = self.image_processor.preprocess(next_image, height=height, width=width)
+        noise = randn_tensor(next_image.shape, generator=generator, device=next_image.device, dtype=next_image.dtype)
+        next_image = next_image + noise_aug_strength * noise
+
+        needs_upcasting = self.vae.dtype == torch.float16 and self.vae.config.force_upcast
+        if needs_upcasting:
+            self.vae.to(dtype=torch.float32)
+
+        next_image_latents = self._encode_vae_image(next_image, device, num_videos_per_prompt, self.do_classifier_free_guidance)
+        next_image_latents = next_image_latents.to(next_image_embeddings.dtype)
+
+        # cast back to fp16 if needed
+        if needs_upcasting:
+            self.vae.to(dtype=torch.float16)
+
+        # Repeat the image latents for each frame so we can concatenate them with the noise
+        # image_latents [batch, channels, height, width] ->[batch, num_frames, channels, height, width]
+        next_image_latents = next_image_latents.unsqueeze(1).repeat(1, num_frames, 1, 1, 1)
+        
+        # 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
+        next_latents = self.prepare_latents(
+            batch_size * num_videos_per_prompt,
+            num_frames,
+            num_channels_latents,
+            height,
+            width,
+            next_image_embeddings.dtype,
+            device,
+            generator,
+            None,
+        )
+
+        image_embeddings = image_embeddings.chunk(2)[1]
+        image_latents = image_latents.chunk(2)[1]
+        
+        # 8. Denoising loop
+        num_warmup_steps = len(timesteps) - num_inference_steps * self.scheduler.order
+        self._num_timesteps = len(timesteps)
+        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
+                next_latent_model_input = torch.cat([next_latents] * 2) if self.do_classifier_free_guidance else next_latents
+                next_latent_model_input = self.scheduler.scale_model_input(next_latent_model_input, t)
+
+                # Concatenate image_latents over channels dimention
+                next_latent_model_input = torch.cat([next_latent_model_input, next_image_latents], dim=2)
+
+                # predict the noise residual
+                noise_pred = self.unet(
+                    next_latent_model_input,
+                    t,
+                    encoder_hidden_states=next_image_embeddings,
+                    added_time_ids=added_time_ids,
+                    return_dict=False,
+                )[0]
+
+                # perform guidance
+                if self.do_classifier_free_guidance:
+                    noise_pred_uncond, noise_pred_cond = noise_pred.chunk(2)
+                    noise_pred = noise_pred_uncond + self.guidance_scale * (noise_pred_cond - noise_pred_uncond)
+
+                with torch.enable_grad():
+                    self.unet.train()
+                    self.unet.enable_gradient_checkpointing()
+                    self.unet.requires_grad_(True)
+                    latents.requires_grad_(True)
+
+                    # Add noise to the latents
+                    noise = torch.rand_like(latents.flatten(0, 1))
+                    timestep = torch.ones(noise.shape[0]).to(noise.device) * t
+                    prev_noised_latents = self.scheduler.add_noise(latents.flatten(0, 1), noise, timestep)
+                    # [batch*frames, channels, height, width] -> [batch, frames, channels, height, width]
+                    prev_noised_latents = prev_noised_latents.reshape(-1, num_frames, *prev_noised_latents.shape[1:])
+                    scaled_prev_noised_latents = self.scheduler.scale_model_input(prev_noised_latents, t)
+                    scaled_prev_noised_latents = torch.cat([scaled_prev_noised_latents, image_latents], dim=2)
+                    
+                    rec_noise_pred = self.unet(
+                        scaled_prev_noised_latents,
+                        t,
+                        encoder_hidden_states=image_embeddings,
+                        added_time_ids=added_time_ids.chunk(2)[1],
+                        return_dict=False,
+                    )[0]
+
+                    sigma = self.scheduler.sigmas[self.scheduler.step_index]
+                    rec_prev_latents = rec_noise_pred * (-sigma / (sigma**2 + 1) ** 0.5) + (prev_noised_latents / (sigma**2 + 1))
+
+                    loss = torch.nn.functional.mse_loss(rec_prev_latents, latents)
+                    # compute grads
+                    grads = torch.autograd.grad(loss, latents)[0]
+
+                    self.unet.eval()
+                    self.unet.requires_grad_(False)
+                    latents.requires_grad_(False)
+
+                noise_pred = noise_pred -  grads * rec_guidance_scale
+
+                # compute the previous noisy sample x_t -> x_t-1
+                next_latents = self.scheduler.step(noise_pred, t, next_latents).prev_sample
+
+                if callback_on_step_end is not None:
+                    callback_kwargs = {}
+                    for k in callback_on_step_end_tensor_inputs:
+                        callback_kwargs[k] = locals()[k]
+                    callback_outputs = callback_on_step_end(self, i, t, callback_kwargs)
+
+                    next_latents = callback_outputs.pop("latents", next_latents)
+
+                if i == len(timesteps) - 1 or ((i + 1) > num_warmup_steps and (i + 1) % self.scheduler.order == 0):
+                    progress_bar.update()
+        
+        # cast back to fp16 if needed
+        if needs_upcasting:
+            self.vae.to(dtype=torch.float16)
+        next_frames = self.decode_latents(next_latents, num_frames, decode_chunk_size)
+        next_frames = tensor2vid(next_frames, self.image_processor, output_type=output_type)
+
+        frames = frames + next_frames
+
         self.maybe_free_model_hooks()
 
         if not return_dict: