We will write down here some quick and useful tips that people working with video might frequently use…
#1-Extracting video frames
ffmpeg -y -i M2U00008.MPG -vframes 10 -ss 00:00:10 -vcodec png -f image2 -s 320×240 x%03d.png
The “-vframes 10” tells ffmpeg to extract the 10 first video frames of the input file. “-ss 00:00:10” tells the program at which time to start the extraction and “-f image2” is necessary to extract single frame files. The “%03d” in the output filename is like the C syntax in printf (creates 3-digit integer numbers to distinguish the different frames filenames). The “-s 320×240” is used to scale the frames in 320×240. If omitted, the original video dimensions will be used.
#2-Converting a sequence of Y video frames into a gray-scale avi-format video
Here we will need to combine imagemagick with ffmpeg. mogrify is a tool from the imagemagick suite.
mogrify -depth 8 -size 176×144 -format png *.Y
The line above will batch create copies of our 176×144, 8bpp .Y frames into .png files.
ffmpeg -f image2 -i CLAIRE%d.png -r 12 -s 176×144 claire_video.avi
all the .png files will be combined into a single .avi file. Now you can see your video file with any common video player. Parameters -s and -f have been explained in tip #1. The -r parameter defines the frame rate. If wrongly provided, the video might become too slow or too fast.
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