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import logging
import os
import shutil
import subprocess
import tempfile
from typing import List, Tuple
import cv2
import numpy as np
def extract_frames(video_path: str) -> Tuple[List[np.ndarray], float, int, int]:
cap = cv2.VideoCapture(video_path)
if not cap.isOpened():
raise ValueError("Unable to open video.")
fps = cap.get(cv2.CAP_PROP_FPS) or 0.0
width = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
height = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
frames: List[np.ndarray] = []
success, frame = cap.read()
while success:
frames.append(frame)
success, frame = cap.read()
cap.release()
if not frames:
raise ValueError("Video decode produced zero frames.")
return frames, fps, width, height
def _transcode_with_ffmpeg(src_path: str, dst_path: str) -> None:
cmd = [
"ffmpeg",
"-y",
"-i",
src_path,
"-c:v",
"libx264",
"-preset",
"veryfast",
"-pix_fmt",
"yuv420p",
"-movflags",
"+faststart",
dst_path,
]
process = subprocess.run(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, check=False)
if process.returncode != 0:
err_msg = process.stderr.decode("utf-8", errors="ignore")
logging.error("ffmpeg failed with code %d: %s", process.returncode, err_msg)
raise RuntimeError(err_msg)
else:
logging.info("ffmpeg success")
def write_video(frames: List[np.ndarray], output_path: str, fps: float, width: int, height: int) -> None:
if not frames:
raise ValueError("No frames available for writing.")
temp_fd, temp_path = tempfile.mkstemp(prefix="raw_", suffix=".mp4")
os.close(temp_fd)
writer = cv2.VideoWriter(temp_path, cv2.VideoWriter_fourcc(*"mp4v"), fps or 1.0, (width, height))
if not writer.isOpened():
os.remove(temp_path)
raise ValueError("Failed to open VideoWriter.")
for frame in frames:
writer.write(frame)
writer.release()
try:
_transcode_with_ffmpeg(temp_path, output_path)
logging.debug("Transcoded video to H.264 for browser compatibility.")
os.remove(temp_path)
except FileNotFoundError:
logging.warning("ffmpeg not found; serving fallback MP4V output.")
shutil.move(temp_path, output_path)
except RuntimeError as exc:
logging.warning("ffmpeg transcode failed (%s); serving fallback MP4V output.", exc)
shutil.move(temp_path, output_path)
class VideoReader:
def __init__(self, video_path: str):
self.video_path = video_path
self.cap = cv2.VideoCapture(video_path)
if not self.cap.isOpened():
raise ValueError("Unable to open video.")
self.fps = self.cap.get(cv2.CAP_PROP_FPS) or 30.0
self.width = int(self.cap.get(cv2.CAP_PROP_FRAME_WIDTH))
self.height = int(self.cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
self.total_frames = int(self.cap.get(cv2.CAP_PROP_FRAME_COUNT))
def __iter__(self):
return self
def __next__(self) -> np.ndarray:
if not self.cap.isOpened():
raise StopIteration
success, frame = self.cap.read()
if not success:
self.cap.release()
raise StopIteration
return frame
def close(self):
if self.cap.isOpened():
self.cap.release()
def __enter__(self):
return self
def __exit__(self, exc_type, exc_val, exc_tb):
self.close()
class AsyncVideoReader:
"""
Async video reader that decodes frames in a background thread.
This prevents GPU starvation on multi-GPU systems by prefetching frames
while the main thread is busy dispatching work to GPUs.
"""
def __init__(self, video_path: str, prefetch_size: int = 32):
"""
Initialize async video reader.
Args:
video_path: Path to video file
prefetch_size: Number of frames to prefetch (default 32)
"""
from queue import Queue
from threading import Thread
self.video_path = video_path
self.prefetch_size = prefetch_size
# Open video to get metadata
self._cap = cv2.VideoCapture(video_path)
if not self._cap.isOpened():
raise ValueError(f"Unable to open video: {video_path}")
self.fps = self._cap.get(cv2.CAP_PROP_FPS) or 30.0
self.width = int(self._cap.get(cv2.CAP_PROP_FRAME_WIDTH))
self.height = int(self._cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
self.total_frames = int(self._cap.get(cv2.CAP_PROP_FRAME_COUNT))
# Prefetch queue
self._queue: Queue = Queue(maxsize=prefetch_size)
self._error: Exception = None
self._finished = False
# Start decoder thread
self._thread = Thread(target=self._decode_loop, daemon=True)
self._thread.start()
def _decode_loop(self):
"""Background thread that continuously decodes frames."""
try:
while True:
success, frame = self._cap.read()
if not success:
break
self._queue.put(frame) # Blocks when queue is full (backpressure)
except Exception as e:
self._error = e
logging.error(f"AsyncVideoReader decode error: {e}")
finally:
self._cap.release()
self._queue.put(None) # Sentinel to signal end
self._finished = True
def __iter__(self):
return self
def __next__(self) -> np.ndarray:
if self._error:
raise self._error
frame = self._queue.get()
if frame is None:
raise StopIteration
return frame
def close(self):
"""Stop the decoder thread and release resources."""
# Signal thread to stop by releasing cap (if not already done)
if self._cap.isOpened():
self._cap.release()
# Drain queue to unblock thread if it's waiting on put()
while not self._queue.empty():
try:
self._queue.get_nowait()
except:
break
def __enter__(self):
return self
def __exit__(self, exc_type, exc_val, exc_tb):
self.close()
class VideoWriter:
def __init__(self, output_path: str, fps: float, width: int, height: int):
self.output_path = output_path
self.fps = fps
self.width = width
self.height = height
self.temp_fd, self.temp_path = tempfile.mkstemp(prefix="raw_", suffix=".mp4")
os.close(self.temp_fd)
# Use mp4v for speed during writing, then transcode
self.writer = cv2.VideoWriter(self.temp_path, cv2.VideoWriter_fourcc(*"mp4v"), self.fps, (self.width, self.height))
if not self.writer.isOpened():
os.remove(self.temp_path)
raise ValueError("Failed to open VideoWriter.")
def write(self, frame: np.ndarray):
self.writer.write(frame)
def close(self):
if self.writer.isOpened():
self.writer.release()
# Transcode phase
try:
_transcode_with_ffmpeg(self.temp_path, self.output_path)
logging.debug("Transcoded video to H.264 for browser compatibility.")
os.remove(self.temp_path)
except FileNotFoundError:
logging.warning("ffmpeg not found; serving fallback MP4V output.")
shutil.move(self.temp_path, self.output_path)
except RuntimeError as exc:
logging.warning("ffmpeg transcode failed (%s); serving fallback MP4V output.", exc)
shutil.move(self.temp_path, self.output_path)
def __enter__(self):
return self
def __exit__(self, exc_type, exc_val, exc_tb):
self.close()
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