video delayed playback

CodingArcher

Hey guys,
how would i implement a recording and playback but with a user defined video delay in displaying the video feed but it not impacting the recordings.
cheers

Mojo

Hi @CodingArcher,
I'm not entirely sure what you mean by "user defined video delay". If you want to add a delay before the camera starts recording, you can simply use Python's time.sleep() function or something equivalent in C++.
Regarding the recording itself, we have an example that only plays the encoded stream here, and another that only encodes (records) it here. You could take the first exmaple and modify it by adding the tofile method on the data packet, that way it will also save the video to a file.

CodingArcher

Mojo Hi Mojo,
sorry for not being specfic enough. What i was trying to say is that i would like to have a playback of the videofeed but with 20seconds but then in another instance i would like to have 30sec.
Having a sleeping function will pause the video capture but thats not what im after. Im looking for being able to record and display (which i am already in real time) but now with the "live view" 20sec behind the real time feed.
hope that makes more sense 🙂

Mojo

I threw together a quick example (below). Basically it uses a timer which starts the ffplay process when it times out, which plays a video file, while it's still being written to. Note: be careful when running this, as when you hit Q to close the ffplay process, it does not terminate the main program and is therefore still writing video data to the file. You have to stop the main program with Ctrl + C.

#!/usr/bin/env python3

import depthai as dai
import subprocess as sp
from os import name as osName
import threading

# Create pipeline
pipeline = dai.Pipeline()

# Define sources and output
camRgb = pipeline.createColorCamera()
videoEnc = pipeline.createVideoEncoder()
xout = pipeline.createXLinkOut()

xout.setStreamName("h264")

# Properties
camRgb.setBoardSocket(dai.CameraBoardSocket.RGB)
camRgb.setResolution(dai.ColorCameraProperties.SensorResolution.THE_4_K)
videoEnc.setDefaultProfilePreset(camRgb.getVideoSize(), camRgb.getFps(), dai.VideoEncoderProperties.Profile.H264_MAIN)

# Linking
camRgb.video.link(videoEnc.input)
videoEnc.bitstream.link(xout.input)

width, height = 720, 500
filename = "video.h264"
command = [
    "ffplay", filename,
    "-x", str(width),
    "-y", str(height),
    "-framerate", "60",
    "-fflags", "nobuffer",
    "-flags", "low_delay",
    "-framedrop",
    "-strict", "experimental",
]

if osName == "nt":  # Running on Windows
    command = ["cmd", "/c"] + command


def playVideo():
    try:
        sp.Popen(command)  # Start playing the video with delay
    except:
        exit("Error: cannot run ffplay!\nTry running: sudo apt install ffmpeg")


delay = 5
timer = threading.Timer(delay, playVideo)

# Connect to device and start pipeline
with dai.Device(pipeline) as device:
    # Output queue will be used to get the encoded data from the output defined above
    q = device.getOutputQueue(name="h264", maxSize=30, blocking=True)

    with open(filename, "wb") as videoFile:
        timer.start()
        try:
            while True:
                data = q.get().getData()  # Blocking call, will wait until new data has arrived
                data.tofile(videoFile)
        except:
            pass