Unable to display results in st.write inside recv

[gauthamk28]

Hi @whitphx thank you for giving this amazing streamlit-webrtc . When I am running the app , I want to display the name of the person detected , when I use print(variable name) , the name of the person is getting printed , whereas when I use st.write(recv) inside recv .

class OpenCVVideoProcessor(VideoProcessorBase):
    def recv(self, frame: av.VideoFrame) -> av.VideoFrame:
    ...
    ...
    st.write(detected_result)

Is there any way to display the result of object detection in html or is there anyway to connect this app with FastAPI , because I need to use this value to do more tasks outside python. I am new so please give any idea which will be helpful for me.

[whitphx]

You cannot use Streamlit methods (st.*) inside recv() because recv() is running in a different thread from the main one.

For your purpose, refer to the object detection demo for example. In this example, the detection result is transferred from recv() to the main script through the Processor instance's attribute and displayed with st.table().

• The processor instance has a queue as its attribute, which is accessible from both the main and recv()'s threads: https://github.com/whitphx/streamlit-webrtc/blob/56d715a76247cd6303c9ddade5bc2a8e430ddc2f/app.py#L344
  • A queue is used here for thread-safety.
• The detected result is put into the queue inside recv(): https://github.com/whitphx/streamlit-webrtc/blob/56d715a76247cd6303c9ddade5bc2a8e430ddc2f/app.py#L397
• The results are pulled from the queue in a main thread: https://github.com/whitphx/streamlit-webrtc/blob/56d715a76247cd6303c9ddade5bc2a8e430ddc2f/app.py#L416-L433