API_Transformers/video_processor.py

import cv2
import numpy as np
import base64
from typing import List
from enum import Enum
from skimage.metrics import structural_similarity as ssim

class FrameSamplingMethod(str, Enum):
   UNIFORM = "uniform"
   CONTENT_AWARE = "content_aware"

def extract_frames(
   video_path: str,
   method: FrameSamplingMethod,
   sampling_rate: int
) -> List[np.ndarray]:
   """
   从视频中提取帧。
   对于UNIFORM方法，sampling_rate表示要提取的总帧数。
   对于CONTENT_AWARE方法，sampling_rate现在也表示要提取的总帧数，但会选择变化最大的帧。
   """
   cap = cv2.VideoCapture(video_path)
   if not cap.isOpened():
       raise IOError(f"Cannot open video file: {video_path}")

   frames = []
   total_frames = int(cap.get(cv2.CAP_PROP_FRAME_COUNT))
   target_size = (420, 280) # (width, height)

   if method == FrameSamplingMethod.UNIFORM:
       if sampling_rate <= 0:
           cap.release()
           return []
       
       # 如果请求的帧数大于总帧数，则返回所有帧
       if sampling_rate >= total_frames:
            while True:
                ret, frame = cap.read()
                if not ret:
                    break
                resized_frame = cv2.resize(frame, target_size)
                frames.append(resized_frame)
            cap.release()
            return frames

       # 计算采样间隔
       step = total_frames / sampling_rate
       for i in range(sampling_rate):
           frame_index = int(i * step)
           cap.set(cv2.CAP_PROP_POS_FRAMES, frame_index)
           ret, frame = cap.read()
           if ret:
               resized_frame = cv2.resize(frame, target_size)
               frames.append(resized_frame)
   
   elif method == FrameSamplingMethod.CONTENT_AWARE:
        if sampling_rate <= 0:
            cap.release()
            return []

        # 如果视频总帧数少于或等于请求的帧数，则返回所有帧
        if total_frames <= sampling_rate:
            while True:
                ret, frame = cap.read()
                if not ret:
                    break
                resized_frame = cv2.resize(frame, target_size)
                frames.append(resized_frame)
            cap.release()
            return frames
        
        # --- Pass 1: 计算所有相邻帧的SSIM分数 ---
        ssim_scores = []
        cap.set(cv2.CAP_PROP_POS_FRAMES, 0)
        ret, prev_frame = cap.read()
        if not ret:
            cap.release()
            return []
        
        prev_frame_gray = cv2.cvtColor(prev_frame, cv2.COLOR_BGR2GRAY)

        for i in range(1, total_frames):
            ret, current_frame = cap.read()
            if not ret:
                break
            
            current_frame_gray = cv2.cvtColor(current_frame, cv2.COLOR_BGR2GRAY)
            score, _ = ssim(prev_frame_gray, current_frame_gray, full=True)
            ssim_scores.append((score, i)) # 存储(ssim_score, frame_index)
            prev_frame_gray = current_frame_gray
        
        # --- 选择变化最大的 n-1 帧 ---
        # 按SSIM分数升序排序 (分数越低，差异越大)
        ssim_scores.sort(key=lambda x: x[0])
        
        # 选择分数最低的 n-1 帧的索引
        selected_indices = {score[1] for score in ssim_scores[:sampling_rate - 1]}
        # 始终包括第一帧 (index 0)
        selected_indices.add(0)

        # --- Pass 2: 根据索引提取帧 ---
        sorted_indices = sorted(list(selected_indices))
        for idx in sorted_indices:
            cap.set(cv2.CAP_PROP_POS_FRAMES, idx)
            ret, frame = cap.read()
            if ret:
                resized_frame = cv2.resize(frame, target_size)
                frames.append(resized_frame)

   cap.release()
   return frames

def encode_frames_to_base64(frames: List[np.ndarray]) -> List[str]:
   """
   将OpenCV帧列表编码为base64字符串列表。
   """
   base64_frames = []
   for frame in frames:
       # 将帧编码为JPEG格式
       _, buffer = cv2.imencode('.jpg', frame)
       # 将缓冲区字节转换为base64字符串
       base64_str = base64.b64encode(buffer).decode('utf-8')
       base64_frames.append(base64_str)
   return base64_frames