How to operate "valve" element

[Olivier Crête]

Hi,

The filesrc element will read from the file as fast as possible and it
is only being slowed down by the application's speed reading from the
appsink. If you set drop=true on the valve, then there is nothing
stopping the filesrc from reading the whole file and promptly dropping
the results. If you want to have something like this, you need to fake
a live source with something like "filesrc ! parsebin ! identity
sync=true ! valve ! appsink". You use parsebin (or the specific element
to parser your file) to put appropriate timestamps on the buffers, then
"identity sync=1" to block the buffers until the timestamp is reached.

Olivier

On Mon, 2020-02-24 at 16:50 -0600, bb wrote:
> Greetings,
> 
> I find the 'valve' element confusing in spite its seemingly simple
> interface.
> I got a simple filesrc -> valve -> appsink pipeline and am trying to use the
> valve to control the flow. Initially the valve is open and all is good. When
> the "drop" property is set to TRUE the new samples stop arriving as
> expected. Now if the "drop" is set to FALSE again I don't get any new
> samples; i find it counterintuitive.
> 
> In an attempt to get this working (e.g. getting samples flowing each time
> the valve is open, regardless of the previous state) I was setting the
> appsink state to GST_STATE_PAUSED whenever valve "drop" is TRUE and to
> GST_STATE_PLAYING when valve "drop" is FALSE. That worked better as appsink
> is getting new samples whenever the valve is open, however the samples
> received on the valve reopen are those that were meant to to be dropped
> while the valve was closed as if they were buffered up and are now being
> pushed to appsink as nothing happened. Is that how it's meant to work? I was
> expecting the samples dropped during valve "drop" == true to be lost
> forever, never reaching the appsink.
> 
> Searching on the web i noticed people suggest setting the sink's "async"
> property to FALSE but that didn't do anything for me.
> 
> Clearly in this simple pipeline I could be controlling the samples within
> appsink "new-sample" callback but i'm intending to use valve elsewhere and
> would like to know how to operate it correctly - as it is looks like i'm
> missing something.
> 
> 
> 
> 
> --
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-- 
Olivier Crête
olivier.crete at collabora.com