镜头分割常常被用于视频智能剪辑、视频关键帧提取等场景。
本文给出一种解决镜头分割问题的思路,可分为两个步骤:
1、根据镜头分割算法对视频进行分割标记
核心在于镜头分割算法,这里简单描述一种算法思路:ratio = different(current_frame_histogram, prevous_frame_histogram) / avgvere_different(previous_frame_histogram),通过大量试验找到合适的ratio 阈值,若ratio大于阈值,则从当前帧分割视频,由于版权原因本文省略具体算法及实现。利用cv2的calcHist计算帧RGB三通道histogram的代码如下:
for id in range(3):
self.current\_hist\_rgb\[id\] = cv2.calcHist(\[frame\], \[0\], None, \[256\], \[0, 255\])
2、 根据分割标记进行实际分割
本文使用ffmpeg进行视频分割(需安装ffmpeg),具体命令如下
ffmpeg -ss starttime -i input.mp4 -t duration -codec copy -codec copy output.mp4 -y
命令中参数的顺序不能任意调整,-ss必须是第一个参数,否则分割后的视频可能出现黑屏,-t参数必须在-i参数后面,否则分割后视频可能出现时长不正确的问题。从实际效果来看,分割点并不准确在-ss参数指定的时间点,而是之前最近的关键帧。
最后,本文采用ffmpeg-python(需要用pip安装)来计算视频pts,具体实现见VideoCutEngine的calcPTS方法。
实现代码:
import cv2
import ffmpeg
import numpy as np
import sys
import os
class VideoCutEngine():
def __init__(self, input):
self.input = input
def calcPTS(self):
try:
probe = ffmpeg.probe(self.input)
except ffmpeg.Error as e:
print(e.stderr, sys.stderr)
return False, 0
video\_stream = next((stream for stream in probe\['streams'\] if stream\['codec\_type'\] == 'video'), None)
if video\_stream is None:
return False, 1
num\_frames = int(video\_stream\['nb\_frames'\])
duration = float(video\_stream\['duration'\])
return True, num\_frames \* 1.0 / duration
def doCut(self, start, duration, output):
cmd = 'ffmpeg -ss {} -i {} -t {} -codec copy -codec copy {} -y'.format(start, self.input, duration, output)
ret = os.system(cmd)
return ret
class SceneSplitEngine():
def __init__(self):
self.frame = None
self.current_hist_rgb = [0, 0, 0]
self.last_hist_rgb = [0, 0, 0]
self.frame_count = 0
self.current_shot_count = 0
self.hist_diff = []
def setFrmae(self,frame):
self.frame = frame
self.frame\_count += 1
self.current\_shot\_count += 1
def doSplit(self):
for id in range(3):
self.current\_hist\_rgb\[id\] = cv2.calcHist(\[frame\], \[0\], None, \[256\], \[0, 255\])
具体算法实现省略。
input = '/data/test.mp4'
if __name__ == '__main__':
sceneSpliter = SceneSplitEngine()
videoCutter = VideoCutEngine(input)
videoCapturer = cv2.VideoCapture(input)
pts = videoCutter.calcPTS()
while True:
ret1, frame = videoCapturer.read()
if ret1 == True:
sceneSpliter.setFrmae(frame)
ret2, start, end = sceneSpliter.doSplit()
if ret2 == True:
duration = max((end -start) / 24, 1)
print(ret2, start / 24, duration)
output = '/data/output{}.mp4'.format(start / 24)
videoCutter.doCut(start / 24, duration, output)
else:
break
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