如何在GStreamer视频流上显示日期(文本覆盖)？

import gi
gi.require_version('Gst', '1.0')
from gi.repository import Gst

# 初始化GStreamer
Gst.init(None)

# 创建管道
pipeline = Gst.Pipeline()

# 创建元素
src = Gst.ElementFactory.make("videotestsrc", "src")
overlay = Gst.ElementFactory.make("textoverlay", "overlay")
sink = Gst.ElementFactory.make("autovideosink", "sink")

# 设置日期覆盖属性
overlay.set_property("text", "Date: %Y-%m-%d")
overlay.set_property("halignment", "right")
overlay.set_property("valignment", "bottom")

# 添加元素到管道
pipeline.add(src)
pipeline.add(overlay)
pipeline.add(sink)

# 连接元素
src.link(overlay)
overlay.link(sink)

# 启动管道
pipeline.set_state(Gst.State.PLAYING)

# 等待管道运行
bus = pipeline.get_bus()
msg = bus.timed_pop_filtered(Gst.CLOCK_TIME_NONE, Gst.MessageType.ERROR | Gst.MessageType.EOS)

# 停止管道
pipeline.set_state(Gst.State.NULL)