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multiply -ss options

Oleksiy Druzhynin
Dear FFmpeg users.

If I use multiply -ss options with the same video

ffmpeg -ss 00:00:05 -i input.mp4
       -ss 00:01:05 -i input.mp4
       -ss 00:03:05 -i input.mp4
       -ss 00:40:05 -i input.mp4
       -map 0:v -frames:v 1 out001.jpg
       -map 1:v -frames:v 1 out002.jpg
       -map 2:v -frames:v 1 out003.jpg
       -map 3:v -frames:v 1 out004.jpg

The same video would be opened few times or it would be opened just once (for the optimization and speed-up purpose)?

Regards,

Oleksii

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Re: multiply -ss options

Moritz Barsnick
On Mon, May 08, 2017 at 02:03:57 +0000, Oleksiy Druzhynin wrote:

> If I use multiply -ss options with the same video
>
> ffmpeg -ss 00:00:05 -i input.mp4
>        -ss 00:01:05 -i input.mp4
>        -ss 00:03:05 -i input.mp4
>        -ss 00:40:05 -i input.mp4
>        -map 0:v -frames:v 1 out001.jpg
>        -map 1:v -frames:v 1 out002.jpg
>        -map 2:v -frames:v 1 out003.jpg
>        -map 3:v -frames:v 1 out004.jpg
>
> The same video would be opened few times or it would be opened just once (for the optimization and speed-up purpose)?

As far as I know, ffmpeg opens each input separately, and leaves the
optimization to the operating system.

In your particular case, I wouldn't know how ffmpeg should know to
"optimize" this better, as your four output streams need to be
available for the output simultaneously. It needs to seek to each of
your four offsets, to collect those streams (or frames in your case). I
think most OSs can do that just fine.

Moritz
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