make screen captures from videos recursive?

[sohlinux]

I have a folder with 50 videos and I need to take some screen shots from each video recursively

the following works for one file only

ffmpeg -i name.mp4 -r 1/20 %03d.jpg

I tried

*.mp4

but it said do I want to overwrite the video? I said no then it stopped so what I am doing wrong?

thanks

[FakeOutdoorsman]

You can use a bash "for" loop:

for f in *.mp4; do ffmpeg -i "$f" -r 1/20 %03d.jpg; done

Unfortunately that will not create unique files names so the next video will overwrite them, or perhaps ffmpeg will halt asking you if you want to overwrite. It's easy to fix. You can give unique output file names:

for f in *.mp4; do ffmpeg -i "$f" -r 1/20 "${f%.mp4}-%03d.jpg"; done

Alternatively, you can make a separate directory for each video.

for f in *.mp4; do mkdir "${f%.mp4}" && ffmpeg -i "$f" -r 1/20 "${f%.mp4}/%03d.jpg"; done

If the output files look too crappy then add "-qscale" as an output option with a value between 2-31 (2 is best quality, and 31 is absolute worst).

[sohlinux]

You can use a bash "for" loop:

for f in *.mp4; do ffmpeg -i "$f" -r 1/20 %03d.jpg; done

Unfortunately that will not create unique files names so the next video will overwrite them, or perhaps ffmpeg will halt asking you if you want to overwrite. It's easy to fix. You can give unique output file names:

for f in *.mp4; do ffmpeg -i "$f" -r 1/20 "${f%.mp4}-%03d.jpg"; done

Alternatively, you can make a separate directory for each video.

for f in *.mp4; do mkdir "${f%.mp4}" && ffmpeg -i "$f" -r 1/20 "${f%.mp4}/%03d.jpg"; done

If the output files look too crappy then add "-qscale" as an output option with a value between 2-31 (2 is best quality, and 31 is absolute worst).

that's awesome! a couple more questions if you dont mind, how do I ensure the screenshot is the the same size as the video? some are 640x480 and some are 720x576 and how can I to take 5 screenshots from each video? I think the current setting takes a shot every x seconds because I am getting more shots from some of the longer videos?

thanks

[FakeOutdoorsman]

how do I ensure the screenshot is the the same size as the video? some are 640x480 and some are 720x576.

By default the outputs will be the same frame size as the input, so you don't have to do anything extra.

how can I to take 5 screenshots from each video? I think the current setting takes a shot every x seconds because I am getting more shots from some of the longer videos?

Probably a dozen ways to do this, but here's a method using the "select" filter. Let's assume your input frame rate is 24.98 or more accurately 24000/1001 (NTSC film) and it is 120 seconds long in duration:

1. (24000/1001) frame rate * 120 duration = ~2877 total frames
2. 2877 / (number of frames desired - 1) = ~719 frames between output images

Please double check my math since I've always been deficient in that area. Which results in:

ffmpeg -i input select="eq(n\,0)+eq(n\,719)+eq(n\,1438)+eq(n\,2157)+eq(n\,2876),setpts=N/((24000/1001)*TB)" output-%03d.png

You probably don't want the very first frame or the very last so you may want to add a few seconds buffer (±3 seconds in this example, or roughly 75 frames) for the first and last values:

ffmpeg -i input select="eq(n\,75)+eq(n\,719)+eq(n\,1438)+eq(n\,2157)+eq(n\,2801),setpts=N/((24000/1001)*TB)" output-%03d.png

It's kind of tricky but can be scripted.

[sohlinux]

By default the outputs will be the same frame size as the input, so you don't have to do anything extra.



Probably a dozen ways to do this, but here's a method using the "select" filter. Let's assume your input frame rate is 24.98 or more accurately 24000/1001 (NTSC film) and it is 120 seconds long in duration:

1. (24000/1001) frame rate * 120 duration = ~2877 total frames
2. 2877 / (number of frames desired - 1) = ~719 frames between output images

Please double check my math since I've always been deficient in that area. Which results in:

ffmpeg -i input select="eq(n\,0)+eq(n\,719)+eq(n\,1438)+eq(n\,2157)+eq(n\,2876),setpts=N/((24000/1001)*TB)" output-%03d.png

You probably don't want the very first frame or the very last so you may want to add a few seconds buffer (±3 seconds in this example, or roughly 75 frames) for the first and last values:

ffmpeg -i input select="eq(n\,75)+eq(n\,719)+eq(n\,1438)+eq(n\,2157)+eq(n\,2801),setpts=N/((24000/1001)*TB)" output-%03d.png

It's kind of tricky but can be scripted.

thanks a lot!