Textoverlay questions

[Nicolas Dufresne]

Le vendredi 09 juin 2017 à 15:35 +0000, William Salibrici a écrit :
> I am using the following simple pipeline segment to add a text area
> under my compositor video output. In a separate thread, I set the
> “text” property once every second to update the rendered
>  text. For my application, the text updates must be real-time. 
> 
> 
>  
> 
> 
> videotestsrc pattern=white ! textoverlay ! queue ! comp.sink_2 
> 
> 
>  
> 
> My development machine is windows 7 and I’m using GStreamer 1.10.4
> with your windows pre-built binaries.
> 
> 
> My overall pipeline runs without errors but the text updates are not
> always 1 second apart. Sometimes there are pauses between updates
> greater than 1 second. Other times updates come back to
>  back with no discernable delay. Sometimes updates appear to be
> skipped altogether [maybe they are just flying by too fast for me to
> see them]. The latency for displaying text seems to vary quite a bit.
> 
> 
> So, here are some questions:
> 
> 
> 
> What is the latency for displaying text [the time between when the
> g_object_set function is called to set the text to be displayed and
> when the text will actually be displayed]?
> 
> Is there any way to achieve a relatively constant latency for
> displaying text? 
> 
> Is there any way force the text to be synchronized with the other
> input video streams to my compositor?

textoverlay has a text pad. You can use this pad to stream text with
timestamp on it. The simply way it to connect "filesrc
location=file.srt ! subparse ! ..." Subpase supports most common text
based sub-title formats, letting you set a timestamp and a duration for
each text. You can of course replace filesrc with an appsrc or fdsrc to
stream the data.

Nicolas
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