Capturing CameraStream raises error "No data, did you record anything?"

I am trying to capture 100 snapshots programatically from my webcam but somehow, the ImageRecorder does not record any image. However, when capturing the images using the dedicated widget button, it works like charm.

This is my code:

First code block (which simply shows the user the webcam input)

from ipywebrtc import CameraStream, ImageRecorder
from time import sleep

camera = CameraStream.facing_user(audio=False)
camera

Second code block (which should capture 100 shots from the camera):

recorder = ImageRecorder(stream=camera)
recorder.recording = True

for i in range(1,100):
    sleep(0.1)
    recorder.save("webcam/" + str(i) + ".png")

Executing the last block, the following error appears:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-9-77bec100e9f4> in <module>
      4 for i in range(1,100):
      5     sleep(0.1)
----> 6     recorder.save("webcam/" + str(i) + ".png")

c:\program files (x86)\microsoft visual studio\shared\python37_64\lib\site-packages\ipywebrtc\webrtc.py in save(self, filename)
    397             filename += '.' + self.format
    398         if len(self.image.value) == 0:
--> 399             raise ValueError('No data, did you record anything?')
    400         with open(filename, 'wb') as f:
    401             f.write(self.image.value)

ValueError: No data, did you record anything?

What am I missing here?

[frostieDE]

It finally works 🎉 In case someone wants to do the same as I want, this is the code:

from ipywebrtc import CameraStream, ImageRecorder
from ipywidgets import Output, VBox

camera = CameraStream.facing_user(audio=False)
camera

recorder = ImageRecorder(stream=camera)
out = Output()

numImage = 0
numImages = 100

def savePicture(_):
    with out:
        global numImage
        global numImages
        if numImage >= numImages:
            return

        out.append_stdout("Image " + str(numImage) + " captured \n")
        recorder.save("webcam/" + str(numImage) + ".png")
        numImage = numImage + 1
        recorder.recording = True
    
recorder.image.observe(savePicture, names=['value'])
VBox([recorder, out])

[martinRenou]

I’m not sure I get why…

This could make it work, but I don’t see why it is needed:

def savePicture(_):
    with out:
        global numImage
        global numImages

        [...]