GstPushSrc create method

[Dass, Reena A Collins]

I’ve developed a plugin based on GstPushSrc. My pipeline has this source plugin, a transform plugin and a sink plugin. The pipe is running in a loop but I want to control when the create method is called. How do I set that up?

 

Reena Dass | Staff Software Engineer | ISR & Space Solutions

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[Tim Müller]

On Thu, 2020-05-07 at 16:49 +0000, Dass, Reena A Collins wrote:

Hi Reena,

> I’ve developed a plugin based on GstPushSrc. My pipeline has this
> source plugin, a transform plugin and a sink plugin. The pipe is
> running in a loop but I want to control when the create method is
> called. How do I set that up?

Why do you want to or need to control that?

Could you provide some more context about what you're trying to achieve
exactly? (big picture)

What kind of source element is it? (audio, video, something else)

Is it a live source? Where does your data come from? Can it be produced
on demand or do you have to wait for it or is it produced in regular
intervals (e.g. at X fps)?

The create method will typically be called whenever a new buffer is
needed, which is typically when downstream (transform ! sink) are done
with the previous buffer and give control back to the source. Assuming
there are no queues in between.

Cheers
 Tim


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[Dass, Reena A Collins]

Thanks for your response Tim.

See my answers below



Hi Reena,

> I’ve developed a plugin based on GstPushSrc. My pipeline has this
> source plugin, a transform plugin and a sink plugin. The pipe is
> running in a loop but I want to control when the create method is
> called. How do I set that up?

Why do you want to or need to control that?

+++++++I need to process data on demand after having created and loading the pipeline once. Now I have no control on the create. I want the create to be called when I need to process a buffer of data.

Could you provide some more context about what you're trying to achieve
exactly? (big picture)

What kind of source element is it? (audio, video, something else)
+++++++It’s a custom source element that I have written, inheriting from GstPushSrc.

Is it a live source? Where does your data come from? Can it be produced
on demand or do you have to wait for it or is it produced in regular
intervals (e.g. at X fps)?
+++++++Yes it is a live source. My pipeline is loaded in a DLL, where each object is created using the factory. I set properties on the Source object when a specific function is called. The create method currently is blocking on that property being set.

The create method will typically be called whenever a new buffer is
needed, which is typically when downstream (transform ! sink) are done
with the previous buffer and give control back to the source. Assuming
there are no queues in between.
+++++++ I can see the create being called when the Sink is done but I now I had to add a wait (using sleep) in the create.
Cheers
 Tim


--
Tim Müller, Centricular Ltd - https://urldefense.proofpoint.com/v2/url?u=http-3A__www.centricular.com&d=DwIGaQ&c=ilBQI1lupc9Y65XwNblLtw&r=HQWJANUP83Z9FphYCG_LvTtNzX_hmziQ8C-qpehNFEA&m=MgxNTYAwKAuF03xEtmBRd4OFHQQ4F7DLdoQLt0RXzQI&s=yJ0j_1zgTpL-bsdUf5V8zKkH6OXTdgh1Rzy9KivJs8Q&e= 

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[Tim Müller]

On Fri, 2020-05-08 at 12:01 +0000, Dass, Reena A Collins wrote:

Hi,

> Yes it is a live source. My pipeline is loaded in a DLL, where each
> object is created using the factory. I set properties on the Source
> object when a specific function is called. The create method
> currently is blocking on that property being set.
>
> (...)
> I can see the create being called when the Sink is done but I now I
> had to add a wait (using sleep) in the create.

That's normal and expected in this case, that ::create() is
blocking/waiting on something for data to be available. Usually that
would be blocked on a file descriptor / socket / handle or a GCond
though.

It sounds like you might want something like appsrc, where you just
call gst_app_src_push_buffer() whenever you have a new buffer
available. (Appsrc will add this to an internal queue and then signal
on a GCond to wake up the ::create() function thread if it's waiting
for a new buffer).

Cheers
 Tim

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Tim Müller, Centricular Ltd - http://www.centricular.com

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