使用OpenCV實現抖音“藍線挑戰”特效。原理比較簡單，當藍線在視頻畫面中滑動，然后從滑過的每一幀中截取部分畫面生成一幅靜態圖片，由于上一幀畫面已經定格，那么通過調整下一幀畫面可以生成各種奇怪的場景。

處理過程可分為幾個步驟：

讀取原始視頻信息（寬、高、fps和總幀數）；

計算藍線在視頻中的移動速度，橫向移動：寬÷總幀數，縱向移動：高÷總幀數；

分解原視頻每一幀畫面，計算藍線在當前幀中的位置；

繪制當前靜態畫面和藍線；

將繪制后的畫面作為幀生成視頻文件。

以藍線從左往右為例：

首先使用OpenCV讀取原始視頻，獲取視頻信息并通過視頻寬與總幀數計算藍線移動速度；

藍線從左往右移動，當藍線滑過第一幀，第一幀畫面上滑過的部分將作為靜態畫面保留到下一幀。因此需要定義一個img來保留之前幀生成的畫面；

當讀取到下一幀畫面frame后，根據當前藍線所處位置對當前幀frame進行裁切，用裁切后的畫面替換掉img上相同位置的畫面。（需要注意的是image_block=frame[0:height,x:width]，這里是圖像高在前寬在后）；

生成畫面之后再使用OpenCV繪制藍線cv2.line(img,(int(x + 3),0),(int(x + 3),height),(255,0,0),3)，藍線寬度設定為3個像素，最后將處理好的畫面寫入視頻文件。

一、藍線從左往右滑動：

from?cv2?import?cv2

#繪制靜態畫面和藍線

def?drawline(frame,img,x,width,height,bluelinespeed):

????bulelinelocation?=?int(x?+?bluelinespeed?+?2)

????if?bulelinelocation?<?width:

????????image_block?=?frame[0:height,int(x):width]

????????tempimg[0:height,int(x):width]?=?image_block

????????cv2.line(img,(bulelinelocation,0),(bulelinelocation,height),(255,0,0),2)

videoCapture?=?cv2.VideoCapture('C:/Users/admin/Desktop/test/video/2.avi')

fps?=?videoCapture.get(cv2.CAP_PROP_FPS)

width?=?int(videoCapture.get(cv2.CAP_PROP_FRAME_WIDTH))

height?=?int(videoCapture.get(cv2.CAP_PROP_FRAME_HEIGHT))

totalCount?=?videoCapture.get(cv2.CAP_PROP_FRAME_COUNT)

size?=?(width,height)

bluelinespeed?=?width /?totalCount?????

videoWriter?=?cv2.VideoWriter('C:/Users/admin/Desktop/test/video/222.avi',cv2.VideoWriter_fourcc('X','V','I','D'),fps,size)

success,frame?=?videoCapture.read()

tempimg?=?frame

img?=?frame

remianing?=?totalCount

x?=?0

while?success?and?remianing?>?0:

????x?=?x?+?bluelinespeed

????drawline(frame,img,x,width,height,bluelinespeed)

????videoWriter.write(img)

????success,frame?=?videoCapture.read()

????remianing?-=?1

效果：

二、藍線從右往左

from?cv2?import?cv2

#繪制靜態畫面和藍線

def?drawline(frame,img,x,width,height,bluelinespeed):

????bulelinelocation?=?int(x?-?bluelinespeed?-?2)

????if?bulelinelocation?>?0:

????????image_block?=?frame[0:height,0:int(x)]

????????tempimg[0:height,0:int(x)]?=?image_block

????????cv2.line(img,(bulelinelocation,0),(bulelinelocation,height),(255,0,0),2)

videoCapture?=?cv2.VideoCapture('C:/Users/admin/Desktop/test/video/2.avi')

fps?=?videoCapture.get(cv2.CAP_PROP_FPS)

width?=?int(videoCapture.get(cv2.CAP_PROP_FRAME_WIDTH))

height?=?int(videoCapture.get(cv2.CAP_PROP_FRAME_HEIGHT))

totalCount?=?videoCapture.get(cv2.CAP_PROP_FRAME_COUNT)

size?=?(width,height)

bluelinespeed?=?width /?totalCount?????

videoWriter?=?cv2.VideoWriter('C:/Users/admin/Desktop/test/video/222.avi',cv2.VideoWriter_fourcc('X','V','I','D'),fps,size)

success,frame?=?videoCapture.read()

tempimg?=?frame

img?=?frame

remianing?=?totalCount

x?=?width

while?success?and?remianing?>?0:

????x?=?x?-?bluelinespeed

????drawline(frame,img,x,width,height,bluelinespeed)

????videoWriter.write(img)

????success,frame?=?videoCapture.read()

????remianing?-=?1

效果：

三、藍線從上往下

from?cv2?import?cv2

#繪制靜態畫面和藍線

def?drawline(frame,img,x,width,height,bluelinespeed):

????bulelinelocation?=?int(x?+?bluelinespeed?+?2)

????if?bulelinelocation?<?height:

????????image_block?=?frame[int(x):height,0:width]

????????tempimg[int(x):height,0:width]?=?image_block

????????cv2.line(img,(0,bulelinelocation),(width,bulelinelocation),(255,0,0),2)

videoCapture?=?cv2.VideoCapture('C:/Users/admin/Desktop/test/video/2.avi')

fps?=?videoCapture.get(cv2.CAP_PROP_FPS)

width?=?int(videoCapture.get(cv2.CAP_PROP_FRAME_WIDTH))

height?=?int(videoCapture.get(cv2.CAP_PROP_FRAME_HEIGHT))

totalCount?=?videoCapture.get(cv2.CAP_PROP_FRAME_COUNT)

size?=?(width,height)

bluelinespeed?=?height?/?totalCount?????

videoWriter?=?cv2.VideoWriter('C:/Users/admin/Desktop/test/video/222.avi',cv2.VideoWriter_fourcc('X','V','I','D'),fps,size)

success,frame?=?videoCapture.read()

tempimg?=?frame

img?=?frame

remianing?=?totalCount

x?=?0

while?success?and?remianing?>?0:

????x?=?x?+?bluelinespeed

????drawline(frame,img,x,width,height,bluelinespeed)

????videoWriter.write(img)

????success,frame?=?videoCapture.read()

????remianing?-=?1

效果：

四、藍線從下往上滑動：

from?cv2?import?cv2

#繪制靜態畫面和藍線

def?drawline(frame,img,x,width,height,bluelinespeed):

????bulelinelocation?=?int(x?- bluelinespeed?-?2)

????if?bulelinelocation?<?height:

????????image_block?=?frame[0:int(x),0:width]

????????tempimg[0:int(x),0:width]?=?image_block

????????cv2.line(img,(0,bulelinelocation),(width,bulelinelocation),(255,0,0),2)

videoCapture?=?cv2.VideoCapture('C:/Users/admin/Desktop/test/video/1.avi')

fps?=?videoCapture.get(cv2.CAP_PROP_FPS)

width?=?int(videoCapture.get(cv2.CAP_PROP_FRAME_WIDTH))

height?=?int(videoCapture.get(cv2.CAP_PROP_FRAME_HEIGHT))

totalCount?=?videoCapture.get(cv2.CAP_PROP_FRAME_COUNT)

size?=?(width,height)

bluelinespeed?=?height?/?totalCount?????

videoWriter?=?cv2.VideoWriter('C:/Users/admin/Desktop/test/video/11.avi',cv2.VideoWriter_fourcc('X','V','I','D'),fps,size)

success,frame?=?videoCapture.read()

tempimg?=?frame

img?=?frame

remianing?=?totalCount

x?=?height

while?success?and?remianing?>?0:

????x?=?x?-?bluelinespeed

????drawline(frame,img,x,width,height,bluelinespeed)

????videoWriter.write(img)

????success,frame?=?videoCapture.read()

????remianing?-=?1

效果：

?

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