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• v4l2 : add a private option for video standard.

  23 mai 2011, par Anton Khirnov

  v4l2 : add a private option for video standard.

• Decoding the h.264 stream from a serial port

  18 mars, par Peter

  I would like to know if there is a reliable way to decode an H.264 NAL stream coming through a serial port using software.

  


  So far, I have managed to decode a single frame using a python script. In this script, I first write the incoming data to a file, and when the end-of-frame marker 00_00_00_01 appears, I display the frame using ffplay.

  


  import serial
import subprocess
import os
import time

ser = serial.Serial('COM3', 115200, timeout=1)
output_file = "output.264"

# Variable to store the ffplay process
ffplay_process = None

# Open the file for writing in binary mode
with open(output_file, "wb") as file:

    print("Writing bytes to output.264. Waiting for the end-of-frame marker 0x00000001.")

    buffer = bytearray()
    marker = b'\x00\x00\x00\x01'

    try:
        while True:
            if ser.in_waiting:  # If there is data in the buffer
                data = ser.read(ser.in_waiting)  # Read all available bytes
                buffer.extend(data)

                # Check if the end-of-frame marker is in the buffer
                while marker in buffer:
                    index = buffer.index(marker) + len(marker)  # Position after the marker
                    frame = buffer[:index]  # Extract the frame
                    buffer = buffer[index:]  # Keep the remaining data

                    print(f"Frame recorded: {len(frame)} bytes")
                    file.write(frame)  # Write the frame to the file
                    file.flush()  # Force writing to disk

                    # Close the ffplay window if it is already open
                    if ffplay_process and ffplay_process.poll() is None:
                        ffplay_process.terminate()
                        ffplay_process.wait()  # Wait for the process to terminate

                    # Play the recorded frame, reopening the window
                    ffplay_process = subprocess.Popen(["ffplay", "-f", "h264", "-i", output_file])

    except KeyboardInterrupt:
        print("\nRecording stopped.")
    finally:
        # Close the serial port and the ffplay process
        ser.close()


  


  However, each time a new end-of-frame marker is detected, the ffplay window closes and reopens to show the next frame. It will flicker when transferring the video. Is there a way to display the frames in the same window for seamless playback when streaming video ?

  


  Or is there a better approach or software that is more suited for this task ? I do not know where to start, so I will be glad for any hints.

  


• How to create video by stitching together images (.png) where the serial on each image file increases by 6

  10 avril 2024, par DataStatsExplorer

  I am trying to create a video (preferably mp4) from a series of png images. However, the name of each image file increases by 6 every frame. For example, I would have depthframe_0000 as the first frame, and depthframe_0001 for the next frame.

  


  There are a few answers that have answered a similar question but I am unable to process the video when the image files are not increasing by 1.

  


  I would like to keep the fps at 5. I am using ffmpeg as the suggested in the answers above but am open to any other suggestion.

  


  The collab code that I have put together is as follows :

  


  import subprocess

# Define the frame rate and the input/output paths
output_fps = 5
input_path = "/content/drive/MyDrive/depth/depthframe_%04d.png"
output_path = "/content/drive/MyDrive/depth.mp4"

# Create a list of the frames
frames = [input_path % i for i in range(0, 2671, 6)]  # Update range as needed

# Write the list of frames to a temporary text file
with open('frames.txt', 'w') as f:
    for frame in frames:
        f.write(f"file '{frame}'\n")

# Create the command
command = [
    "ffmpeg",
    "-f", "concat",
    "-safe", "0",
    "-i", "frames.txt",
    "-c:v", "libx264",
    "-pix_fmt", "yuv420p",
    output_path
]

# Run the command
subprocess.run(command, check=True)