How can we use 'SPMD' for 'VideoReader'?

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MOHIT
MOHIT 2016-6-16
编辑： MOHIT 2016-6-17
hi, I want to do do some video quality reduction fastly, I am using parallel computing , but this error is coming: 'Cannot call READ method after using READFRAME or HASFRAME methods or setting the CURRENTTIME property. Recreate the object to read a frame at a specific frame index'
my code is
videoSrc = VideoReader('rhinos.avi');
% v = VideoWriter('newfile.avi');
% open(v)
spmd
if labindex==1
v = VideoWriter('newfile.avi');
open(v)
for sr = 1:700
huo = read(videoSrc,sr);
RGB2 = imresize(huo, [300 NaN]);
writeVideo(v,RGB2)
% waitbar(sr / videoSrc.NumberOfFrames)
end
close(v)
else
R = rand(4,4);
end
end

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采纳的回答

Sean de Wolski
Sean de Wolski 2016-6-16
Use readFrame() instead of read(). I'd also recommend building the videoSrc on the worker.
spmd
if labindex==1
videoSrc = VideoReader('rhinos.avi');
for ii = 1:700
if hasFrame(videoSrc)
huo = readFrame(videoSrc);
else
break
end
end
end
end

更多回答（1 个）

Steven Lord
Steven Lord 2016-6-16
Writing video to a file seems like an inherently serial operation since you care about the order in which the frames are written to the file. So I wouldn't try to parallelize this.
Picture watching Star Wars if the Death Star exploded first, then Princess Leia was rescued, then Luke and Obi-Wan met Han Solo in the cantina, then Luke was flying his X-Wing toward the Death Star trench. It doesn't really make sense out of order, does it?
  1 个评论
MOHIT
MOHIT 2016-6-17
编辑：MOHIT 2016-6-17
hi, yes you are right, output video needs to be in a sequence and this is the reason I am using 'spmd' not 'parfor'. Because 'spmd' gives results in an organised way.
see this:
spmd
if labindex==1
dataToSend=1:10
elseif labindex==2
dataToSend=1:2:10
elseif labindex==3
dataToSend=1:3:10
elseif labindex==4
dataToSend=1:4:10
end
end

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