Trying to build a very simple Python program to open the webcam on my MacBook and display that on the screen. However, I cannot get the Python version of my pipeline to display the webcam video, and I get garbled / scrolling green lines.
Would like to understand where I went wrong and how I can fix the program.
So far, I have the following program:
import os
import sys
import gi
gi.require_version('Gst', '1.0')
gi.require_version('GstVideo', '1.0')
gi.require_version('GLib', '2.0')
gi.require_version('GObject', '2.0')
from gi.repository import GObject, Gst, GstVideo
GObject.threads_init()
Gst.init(None)
class GstCaps(object):
def __init__(self, caps_string):
self.caps_string = caps_string
def __new__(cls, caps_string):
cf = Gst.ElementFactory.make('capsfilter', None)
caps = Gst.Caps.from_string(caps_string)
cf.set_property('caps', caps)
return cf
class Webcam(object):
# macOS, open webcam and display on screen
# ./gst-launch-1.0 -v -e
# avfvideosrc device-index=0 !
# "video/x-raw, width=1280, height=720, format=(string)YUY2, texture-target=rectangle" !
# rawvideoparse width=1280 height=720 format=yuy2 !
# queue !
# autovideoconvert !
# autovideosink
def __init__(self, device_index: int = 0):
self.mainloop = GObject.MainLoop()
self.pipeline = Gst.ElementFactory.make('pipeline', 'pipeline')
self.source = Gst.ElementFactory.make('avfvideosrc', 'source')
self.source.set_property('device-index', device_index)
self.caps = GstCaps('video/x-raw, width=1280, height=720, format=(string)YUY2, texture-target=rectangle')
# self.source.set_property('caps', caps)
self.rawvideoparse = Gst.ElementFactory.make('rawvideoparse', 'rawvideoparse')
self.rawvideoparse.set_property('width', 1280)
self.rawvideoparse.set_property('height', 720)
self.rawvideoparse.set_property('format', 'yuy2')
self.queue = Gst.ElementFactory.make('queue', 'queue')
self.autovideoconvert = Gst.ElementFactory.make('autovideoconvert', 'autovideoconvert')
self.autovideosink = Gst.ElementFactory.make('autovideosink', 'autovideosink')
if (not self.pipeline or
not self.source or
not self.caps or
not self.rawvideoparse or
not self.queue or
not self.autovideoconvert or
not self.autovideosink
):
print('ERROR: Not all elements could be created.')
sys.exit(1)
self.pipeline.add(self.source)
self.pipeline.add(self.rawvideoparse)
self.pipeline.add(self.queue)
self.pipeline.add(self.autovideoconvert)
self.pipeline.add(self.autovideosink)
linked = self.source.link(self.rawvideoparse)
linked = linked and self.rawvideoparse.link(self.queue)
linked = linked and self.queue.link(self.autovideoconvert)
linked = linked and self.autovideoconvert.link(self.autovideosink)
if not linked:
print("ERROR: Elements could not be linked")
sys.exit(1)
self.bus = self.pipeline.get_bus()
self.bus.add_signal_watch()
self.bus.connect('message::eos', self.on_eos)
self.bus.connect('message::error', self.on_error)
def run(self):
self.pipeline.set_state(Gst.State.PLAYING)
self.mainloop.run()
def quit(self):
self.pipeline.set_state(Gst.State.NULL)
self.mainloop.quit()
def on_eos(self, bus, message):
self.quit()
def on_error(self, bus, message):
print(f'ERROR: {message.parse_error()}' )
self.quit()
webcam = Webcam()
webcam.run()
With this program, I get the following video:
When I run the pipeline from the command line, I get the proper video output as seen below:
gst-launch-1.0 -v -e avfvideosrc device-index=1 ! \
"video/x-raw, width=1280, height=720, format=(string)YUY2, texture-target=rectangle" ! \
rawvideoparse width=1280 height=720 format=yuy2 ! \
queue ! \
autovideoconvert ! \
autovideosink
The output from the Python program looks very familiar to a pipeline error when the format is not specified correctly. I had run into this when I was learning how to setup the pipeline in the command line.
It was probably too late when I posted and missed a very obvious step, so posting the answer in case future Google searches come here.
I had forgotten to add the
capsbetweenavfvideosrcandrawvideoparse. Updated full code below: