Get image buffer from local video stream

[Theuuu]

Hello guys,

I'm new to GStreamer and I'm trying to figure out how to extract an image
buffer during a local video stream.

I've seen some posts talking about appsink, but I haven't had a good example
yet.

And I've read this :
https://gstreamer.freedesktop.org/documentation/application-development/advanced/buffering.html#stream-buffering

Can someone help me out ?

Thanks in advance !



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[Gst-Geek]

Hi Theuuu,

Can you elaborate on what you actually want ??
Do you want to capture video as Image thumbnails ??

In case if you want image thumb nail then you are refering to wrong
document.

~ Vinod



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[Theuuu]

No, I would like to know if there is a way to sequence a video file to
navigate through it by frames.
Afterwards, I'd also like to get the image buffer corresponding to a
specific frame.



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[HermannSW]

multifilesink does what you want:
https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-good/html/gst-plugins-good-plugins-multifilesink.html



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[Theuuu]

Can I get the image data into something like pixel array instead of solid file? 

Le 24 nov. 2017 2:27 PM, "HermannSW" <[hidden email]> a écrit :

multifilesink does what you want:
https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-good/html/gst-plugins-good-plugins-multifilesink.html



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[HermannSW]

> Can I get the image data into something like pixel array instead of solid
file?
>
Others may know.

From a performance perspective I would store the files of multifilesink
under "/dev/shm", a tmpfs filesystem under many Unix-like OSes (exists even
on Raspbian).

All files will end up in memory which is efficient, but they are paged and
not contiguous.
For getting access to a single of those frames as pixel array in memory you
would have to read them (eg. with fopen/fseek/ftell/fread).
If you do that on a one frame after the other basis, your memory consumption
would be N+1 frames, not bad compared to the N frames memory consumption you
requested.



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[Theuuu]

First of all, I'm actually working under Windows, not Linux.

Second, isn't there a Gstreamer tool that would prevent me from reading the file and seeking the cursor by myself? 

Thanks for your response by the way.

Le 24 nov. 2017 19:50, "HermannSW" <[hidden email]> a écrit :

> Can I get the image data into something like pixel array instead of solid
file?
>

Others may know.

From a performance perspective I would store the files of multifilesink
under "/dev/shm", a tmpfs filesystem under many Unix-like OSes (exists even
on Raspbian).

All files will end up in memory which is efficient, but they are paged and
not contiguous.
For getting access to a single of those frames as pixel array in memory you
would have to read them (eg. with fopen/fseek/ftell/fread).
If you do that on a one frame after the other basis, your memory consumption
would be N+1 frames, not bad compared to the N frames memory consumption you
requested.

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[Martin Vachovski]

Hi Herman

>>> Can I get the image data into something like pixel array instead of solid file?

It looks like you can use a

appsink

element. It allows for extracting of data from a pipeline into your app

You can make a pipeline like

autovideosrc ! videoconvert ! video/x-raw,format=rgb,width=640,height=480,framerate=20/1 ! appsink name="appsink_element" emit-signals=true

Then in your app you can register a callback

when a 

"new-sample"

signal arrives.

Have a look at the element's documentation

https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-base-libs/html/gst-plugins-base-libs-appsink.html

Hope that's what you are looking for

Martin

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From: gstreamer-devel <[hidden email]> on behalf of Théo LAVAUX <[hidden email]>
Sent: Friday, November 24, 2017 7:27 PM
To: Discussion of the development of and with GStreamer
Subject: Re: Get image buffer from local video stream

 

First of all, I'm actually working under Windows, not Linux.

Second, isn't there a Gstreamer tool that would prevent me from reading the file and seeking the cursor by myself? 

Thanks for your response by the way.

Le 24 nov. 2017 19:50, "HermannSW" <[hidden email]> a écrit :

> Can I get the image data into something like pixel array instead of solid
file?
>

Others may know.

From a performance perspective I would store the files of multifilesink
under "/dev/shm", a tmpfs filesystem under many Unix-like OSes (exists even
on Raspbian).

All files will end up in memory which is efficient, but they are paged and
not contiguous.
For getting access to a single of those frames as pixel array in memory you
would have to read them (eg. with fopen/fseek/ftell/fread).
If you do that on a one frame after the other basis, your memory consumption
would be N+1 frames, not bad compared to the N frames memory consumption you
requested.

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