Dynamic text-overlay on live-stream using gst-launch-1.0

Mon Feb 27 15:05:53 UTC 2017

Nicolas, thank you for your response.  fdsrc seems like it would be a good
solution, but I'm having issues getting it to work.

It seems like I need to specify the caps after the fdsrc, otherwise it
fails in other ways.  e.g.

Specifying text/x-raw:

tail -f /home/pi/test.txt | /opt/gst/bin/gst-launch-1.0 fdsrc fd=0 !
"text/x-raw" ! txt. videotestsrc ! videoconvert ! decodebin ! textoverlay
name=txt ! omxh264enc target-bitrate=800000 control-rate=3 ! tcpserversink
host=0.0.0.0 port=9000

Results in:

Pipeline is PREROLLING ...
ERROR: from element /GstPipeline:pipeline0/GstCapsFilter:capsfilter0:
Filter caps do not completely specify the output format
Additional debug info:
gstcapsfilter.c(455): gst_capsfilter_prepare_buf ():
/GstPipeline:pipeline0/GstCapsFilter:capsfilter0:
Output caps are unfixed: text/x-raw, format=(string){ pango-markup, utf8 }
ERROR: pipeline doesn't want to preroll.

Specifying text/plain:

tail -f /home/pi/test.txt | /opt/gst/bin/gst-launch-1.0 fdsrc fd=0 !
"text/plain" ! txt. videotestsrc ! videoconvert ! decodebin ! textoverlay
name=txt ! omxh264enc target-bitrate=800000 control-rate=3 ! tcpserversink
host=0.0.0.0 port=9000

Results in:

0:00:00.501757360  4549  0x1e085c0 ERROR           GST_PIPELINE
grammar.y:714:gst_parse_perform_link: could not link fdsrc0 to txt, txt
can't handle caps text/plain
WARNING: erroneous pipeline: could not link fdsrc0 to txt, txt can't handle
caps text/plain

No caps at all:

tail -f /home/pi/test.txt | /opt/gst/bin/gst-launch-1.0 fdsrc fd=0 ! txt.
videotestsrc ! videoconvert ! decodebin ! textoverlay name=txt !
 omxh264enc target-bitrate=800000 control-rate=3 ! tcpserversink
host=0.0.0.0 port=9000

Results in:

Pipeline is PREROLLING ...
WARNING: from element /GstPipeline:pipeline0/GstTextOverlay:txt: Could not
multiplex stream.
Additional debug info:
gstbasetextoverlay.c(2449): gst_base_text_overlay_video_event ():
/GstPipeline:pipeline0/GstTextOverlay:txt:
received non-TIME newsegment event on video input
WARNING: from element /GstPipeline:pipeline0/GstDecodeBin:decodebin0:
Delayed linking failed.
Additional debug info:
./grammar.y(510): gst_parse_no_more_pads ():
/GstPipeline:pipeline0/GstDecodeBin:decodebin0:
failed delayed linking some pad of GstDecodeBin named decodebin0 to some
pad of GstTextOverlay named txt
ERROR: from element /GstPipeline:pipeline0/GstVideoTestSrc:videotestsrc0:
Internal data stream error.
Additional debug info:
gstbasesrc.c(2951): gst_base_src_loop ():
/GstPipeline:pipeline0/GstVideoTestSrc:videotestsrc0:
streaming stopped, reason not-linked (-1)
ERROR: pipeline doesn't want to preroll.

There is some information here (regarding the older version of gst-launch):
http://gstreamer-devel.966125.n4.nabble.com/Dynamic-text-again-td3676141.html

And that links to this bug that was resolved (again, old gst-launch):
https://bugzilla.gnome.org/show_bug.cgi?id=654959

I've seen a couple examples which used the "text/plain" caps.

I'm certainly open to cracking open the Python lib and giving it a shot.  I
would need to read up on it a bit and I'm not familiar with the appsrc,
either, but that's something else I'm open to. I have done very basic stuff
with the Python libs but nothing too fancy or dynamic (basic pipelines, no
more complex than I would get from gst-launch-1.0).

What would you recommend?  Is there an example or resource you could point
me towards?

Thank you for your help

On Sun, Feb 26, 2017 at 2:46 PM, Nicolas Dufresne <nicolas at ndufresne.ca>
wrote:

> Le dimanche 26 février 2017 à 06:18 -0800, Adam Plocher a écrit :
> > Hello, I apologize if I'm posting this in the wrong place. I've
> > previously asked this on stackoverflow and never got a response: http
> > ://stackoverflow.com/questions/42128804/polling-a-text-file-and-
> > overlaying-the-result-in-gstreamer
> >
> > I have a Raspberry Pi with a camera and I'm live streaming that back
> > to another unit (it's for a baby monitor).  On the same Pi, I have a
> > temperature sensor that is dumping the current temp to a file every 5
> > seconds.
> >
> > My question: Is it possible to somehow poll that txt file and update
> > a text-overlay on the live stream based on the current contents of
> > that file?
>
> filsesrc does not have this feature unfortunatly. I believe using
> fdsrc, you could:
>
>   tail -f text.txt | gst-launch-1.0 fdsrc ! ...
>
> Let me know if that is a good work-around. If you are writing an app,
> this can be done with a pipe, or if you prefer, with appsrc.
>
> >
> > I've tried using a filesrc and subparse, and it will grab it
> > initially if I format the input text file properly, but it doesn't
> > seem to update itself:
> >
> > gst-launch-1.0 -v \
> >     filesrc location=/home/pi/temp.txt ! subparse ! txt. rpicamsrc
> > awb-mode=0 awb-gain-red=1 awb-gain-blue=2 rotation=0 bitrate=820000
> > preview=false brightness=67 contrast=30 sharpness=40 \
> >     ! video/x-h264,width=800,height=480,framerate=10/1 \
> >     ! h264parse ! decodebin ! videoconvert ! clockoverlay shaded-
> > background=true draw-shadow=true font-desc="Nimbus Mono" \
> >     ! textoverlay name=txt shaded-background=yes \
> >     ! omxh264enc control-rate=3 target-bitrate=850000 \
> >     ! tcpserversink host=0.0.0.0 port=5555 sync=true
> >
> > The input file looks like this:
> > 1
> > 00:00:00,000 --> 99:59:59,000
> > 69 degrees
> > Thank you!
> > _______________________________________________
> > gstreamer-devel mailing list
> > gstreamer-devel at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/gstreamer-devel
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