example_usage.py

import io
import json
import numpy as np
import torch
import webdataset as wds
from PIL import Image
from concurrent.futures import ThreadPoolExecutor
import os
from huggingface_hub import HfApi

# 🚀 Speed up HF transfers
os.environ["HF_HUB_ENABLE_HF_TRANSFER"] = "1"

class CARLAVideoLoader:
    def __init__(
        self,
        hf_repo="mkxdxd/carla-dataset",
        town="Town01",
        actor_type="pedestrian",
        frames_per_scene=93,
        batch_size=1,
        num_workers=4,
        decode_workers=32,
        shuffle=True
    ):
        """
        Custom video loader for CARLA Stage2 dataset in WebDataset format.
        Optimized for 1-tar-N-scenes format with parallel decoding.
        """
        self.hf_repo = hf_repo
        self.town = town
        self.actor_type = actor_type
        self.frames_per_scene = frames_per_scene
        self.batch_size = batch_size
        self.num_workers = num_workers
        self.decode_workers = decode_workers
        self.shuffle = shuffle
        
        # 1. Get tar URLs from HuggingFace Hub
        api = HfApi()
        all_files = api.list_repo_files(repo_id=hf_repo, repo_type="dataset")
        
        self.tar_urls = []
        prefix = f"{town}/{actor_type}/"
        for f in all_files:
            if f.startswith(prefix) and f.endswith(".tar"):
                self.tar_urls.append(f"https://huggingface.co/datasets/{hf_repo}/resolve/main/{f}")
        
        if not self.tar_urls:
            raise ValueError(f"No tar files found for {town}/{actor_type} in {hf_repo}")
        
        print(f"✅ Found {len(self.tar_urls)} shards for {town}/{actor_type}")
        
        # 2. Build WebDataset pipeline
        self.dataset = (
            wds.WebDataset(self.tar_urls, shardshuffle=self.shuffle, handler=wds.warn_and_continue)
            .to_tuple("__key__", "rgb.png", "depth.npy", "camera.json", "metadata.json", handler=wds.warn_and_continue)
            .map(lambda x: (
                x[0],
                {
                    "rgb.png": x[1],
                    "depth.npy": x[2],
                    "camera.json": x[3],
                    "metadata.json": x[4],
                }
            ), handler=wds.warn_and_continue)
            .compose(self._frames_to_video_sequence)
        )
        
        # 3. Create DataLoader
        self.dataloader = torch.utils.data.DataLoader(
            self.dataset,
            batch_size=self.batch_size,
            num_workers=self.num_workers,
            prefetch_factor=2,
            persistent_workers=True,
            pin_memory=True,
            # Since our compose function yields dictionaries, we handle collate carefully
            # or just yield them one by one if batch_size=1
            collate_fn=self._collate_fn
        )

    def _decode_frame(self, sample):
        """Decodes raw bytes into tensors."""
        # RGB: png -> PIL -> Tensor (3, H, W)
        rgb = Image.open(io.BytesIO(sample["rgb.png"])).convert("RGB")
        rgb = torch.from_numpy(np.array(rgb)).permute(2, 0, 1)

        # Depth: npy -> Tensor (H, W)
        depth = np.load(io.BytesIO(sample["depth.npy"]))
        depth = torch.from_numpy(depth)

        # JSONs
        camera = json.loads(sample["camera.json"])
        metadata = json.loads(sample["metadata.json"])

        return rgb, depth, camera, metadata

    def _frames_to_video_sequence(self, it):
        """WebDataset 'compose' function to group individual frames into full videos."""
        buffer = []
        
        for key, sample in it:
            buffer.append(sample)
            
            if len(buffer) == self.frames_per_scene:
                # 🚀 Parallel decoding for high performance
                with ThreadPoolExecutor(max_workers=self.decode_workers) as executor:
                    decoded = list(executor.map(self._decode_frame, buffer))
                
                # Unpack and stack
                rgbs = torch.stack([d[0] for d in decoded])      # (T, 3, H, W)
                depths = torch.stack([d[1] for d in decoded])    # (T, H, W)
                cameras = [d[2] for d in decoded]
                metas = [d[3] for d in decoded]
                
                # key example: Town01/pedestrian/scene_0001_000
                # base_key will be scene_0001
                base_key = key.rsplit("_", 1)[0]
                
                yield {
                    "video": rgbs,          # (93, 3, 704, 1280)
                    "depth": depths,        # (93, 704, 1280)
                    "camera": cameras,      # list of 93 dicts
                    "metadata": metas,      # list of 93 dicts
                    "scene_id": base_key
                }
                buffer = []

    def _collate_fn(self, batch):
        """
        Handle batching. 
        If batch_size > 1, tensors are stacked, metadata remains as lists.
        """
        if len(batch) == 0:
            return {}
        
        res = {
            "video": torch.stack([b["video"] for b in batch]),     # (B, T, 3, H, W)
            "depth": torch.stack([b["depth"] for b in batch]),     # (B, T, H, W)
            "scene_id": [b["scene_id"] for b in batch],
            "camera": [b["camera"] for b in batch],                # (B, T, dict)
            "metadata": [b["metadata"] for b in batch],            # (B, T, dict)
        }
        return res

    def __iter__(self):
        return iter(self.dataloader)

# --- Example Usage ---
if __name__ == "__main__":
    import time

    print("🚀 Initializing CARLA Video Loader...")
    loader = CARLAVideoLoader(
        hf_repo="mkxdxd/carla-dataset",
        town="Town01",
        actor_type="pedestrian",
        batch_size=2,      # Loading 2 videos at once
        num_workers=4,     # 4 DataLoader workers
        decode_workers=16  # 16 threads for PNG decoding per scene
    )

    print("🎬 Starting stream...")
    start_time = time.time()
    
    for i, batch in enumerate(loader):
        print(f"\n📦 Batch {i+1}")
        print(f"   - Video Shape: {batch['video'].shape}") # (B, 93, 3, 704, 1280)
        print(f"   - Depth Shape: {batch['depth'].shape}") # (B, 93, 704, 1280)
        print(f"   - Scenes: {batch['scene_id']}")
        
        # Access first frame of first video in batch
        first_frame_meta = batch['metadata'][0][0]
        print(f"   - Meta (B0, T0): {first_frame_meta['town']}, frame {first_frame_meta['frame_id']}")
        
        if i >= 2: # Just test a few batches
            break
            
    total_time = time.time() - start_time
    print(f"\n✅ Test finished in {total_time:.2f}s")