[BUG] UDP messages can be too long, aren't broken up

Describe the bug When utilizing UDP streaming as described in the docs, a resolution, bitrate, etc higher than shown easily cause an OSError: [Errno 90] Message too long. This appears to be because the UDP packets are larger than allowed by the OS, and need to be split up.

To Reproduce Use a resolution and bitrate large enough to create big packets. Example script (must change target ip):

#!/usr/bin/python3

import socket
import time

from picamera2 import Picamera2
from picamera2.encoders import H264Encoder
from picamera2.outputs import FileOutput

picam2 = Picamera2()
video_config = picam2.create_video_configuration({"size": (1640, 1232)})
picam2.configure(video_config)
encoder = H264Encoder(1000000, repeat=True)

with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as sock:
    sock.connect(("10.11.9.112", 1234))
    stream = sock.makefile("wb")
    picam2.start_recording(encoder, FileOutput(stream))
    try:
        time.sleep(10000)
    finally:
        picam2.stop_recording()

Expected behaviour No crashes because of UDP packets that are too big.

Console Output, Screenshots

Traceback (most recent call last):
  File "/usr/lib/python3.9/threading.py", line 954, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.9/threading.py", line 892, in run
    self._target(*self._args, **self._kwargs)
  File "/home/pi/.local/lib/python3.9/site-packages/picamera2/encoders/v4l2_encoder.py", line 190, in thread_poll
    self.outputframe(b, keyframe, (buf.timestamp.secs * 1000000) + buf.timestamp.usecs)
  File "/home/pi/.local/lib/python3.9/site-packages/picamera2/encoders/encoder.py", line 183, in outputframe
    out.outputframe(frame, keyframe, timestamp)
  File "/home/pi/.local/lib/python3.9/site-packages/picamera2/outputs/fileoutput.py", line 77, in outputframe
    self._write(frame, timestamp)
  File "/home/pi/.local/lib/python3.9/site-packages/picamera2/outputs/fileoutput.py", line 95, in _write
    self._fileoutput.write(frame)
  File "/usr/lib/python3.9/socket.py", line 722, in write
    return self._sock.send(b)
OSError: [Errno 90] Message too long

Hardware : Raspberry Pi 4, Raspbian Bullseye, IMX219 (Camera v2.1)

Additional context TCP streaming works fine, but is not applicable to our use case where we can’t directly access the device.

[chrisruk]

Yes I think you’re write it might be tricky to fix in FileOutput. I’m just having a little look into UDP based protocols such as RTP. But will do some more investigation into how they work.

It sounds like RTP might be able to split the payload for us, as well as detecting out of order delivery and packet loss.

[chrisruk]

Thanks for reporting, will have a look at this