用Python监控NASA TV直播画面的实现步骤
https://replit.com/@PaoloAmoroso/spacestills
这是一个具有GUI的简单系统，它访问feed流并从Web下载数据。该程序仅需350行代码，并依赖于一些开源的Python库。
关于程序Spacestills会定期从feed流中下载NASA TV静止帧并将其显示在GUI中。该程序可以校正帧的纵横比，并将其保存为PNG格式。它会自动下载最新的帧，并提供手动重新加载，禁用自动重新加载或更改下载频率的选项。Spacestillsis是一个比较初级的版本，但是它可以做一些有用的事情：捕获并保存NASA TV直播的太空事件图像。太空爱好者经常在社交网络或论坛共享他们从NASA TV手动获取的屏幕截图。Spacestills节省了使用屏幕捕获工具的时间，并保存了可供共享的图像文件。您可以在Replit上在线运行Spacestills。
开发环境笔者用Replit开发了Spacestills。Replit是云上的开发，部署和协作环境，它支持包括Python在内的数十种编程语言和框架。作为Chrome操作系统和云计算爱好者，笔者非常喜欢Replit，因为它可以在浏览器中完全正常运行，无需下载或安装任何内容。
资源和依赖包Spacestills依赖于一些外部资源和Python库。
NASA TV feed 流肯尼迪航天中心的网站上有一个页面，其中包含精选的NASA视频流，包括NASA电视公共频道。feed流显示最新的静止帧并自动更新。每个feed都带有三种尺寸的帧，Spacestills依赖于具有704x408像素帧的最大NASA TV feed流。最大更新频率为每45秒一次。因此，检索最新的静止帧就像从feed流的URL下载JPEG图像一样简单。原始图像被垂直拉伸，看起来很奇怪。因此，该程序可以通过压缩图像并生成未失真的16：9版本来校正纵横比。
Python因PySimpleGUI的原因需要安装 Python 3.6 版本。
第三方库 Pillow：图像处理 PySimpleGUI：GUI框架（Spacestills使用Tkinter后端） Request：HTTP请求完整代码from io import BytesIOfrom datetime import datetime, timedeltafrom pathlib import Pathimport requestsfrom requests.exceptions import Timeoutfrom PIL import Imageimport PySimpleGUI as sgFEED_URL = ’https://science.ksc.nasa.gov/shuttle/countdown/video/chan2large.jpg’# Frame size without and with 16:9 aspect ratio correctionWIDTH = 704HEIGHT = 480HEIGHT_16_9 = 396# Minimum, default, and maximum autoreload interval in secondsMIN_DELTA = 45DELTA = MIN_DELTAMAX_DELTA = 300class StillFrame(): '''Holds a still frame.The image is stored as a PNG PIL.Image and kept in PNG format. Attributes ----------image : PIL.Image A still frameoriginal : PIL.Image Original frame with wchich the instance is initialized, cached in case of resizing to the original sizeMethods -------bytes : Return the raw bytesresize : Resize the screenshotnew_size : Calculate new aspect ratio ''' def __init__(self, image):'''Convert the image to PNG and cache the converted original.Parameters---------- image : PIL.ImageImage to store'''self.image = imageself._topng()self.original = self.image def _topng(self):'''Convert image format of frame to PNG.Returns------- StillFrameFrame with image in PNG format'''if not self.image.format == ’PNG’: png_file = BytesIO() self.image.save(png_file, ’png’) png_file.seek(0) png_image = Image.open(png_file) self.image = png_imagereturn self def bytes(self):'''Return raw bytes of a frame image.Returns------- bytesByte stream of the frame image'''file = BytesIO()self.image.save(file, ’png’)file.seek(0)return file.read() def new_size(self):'''Return image size toggled between original and 16:9.Returns------- 2-tupleNew size'''size = self.image.sizeoriginal_size = self.original.sizenew_size = (WIDTH, HEIGHT_16_9) if size == original_size else (WIDTH, HEIGHT)return new_size def resize(self, new_size):'''Resize frame image.Parameters---------- new_size : 2-tupleNew sizeReturns------- StillFrameFrame with image resized'''if not(self.image.size == new_size): self.image = self.image.resize(new_size)return self def make_blank_image(size=(WIDTH, HEIGHT)): '''Create a blank image with a blue background.Parameters ----------size : 2-tuple Image sizeReturns -------PIL.Image Blank image ''' image = Image.new(’RGB’, size=size, color=’blue’) return imagedef download_image(url): '''Download current NASA TV image. Parameters ----------url : str URL to download the image fromReturns -------PIL.Image Downloaded image if no errors, otherwise blank image ''' try:response = requests.get(url, timeout=(0.5, 0.5))if response.status_code == 200: image = Image.open(BytesIO(response.content))else: image = make_blank_image() except Timeout:image = make_blank_image() return imagedef refresh(window, resize=False, feed=FEED_URL): '''Display the latest still frame in window.Parameters ----------window : sg.Window Window to display the still tofeed : string Feed URLReturns -------StillFrame Refreshed screenshot ''' still = StillFrame(download_image(feed)) if resize:still = change_aspect_ratio(window, still, new_size=(WIDTH, HEIGHT_16_9)) else:window[’-IMAGE-’].update(data=still.bytes()) return stilldef change_aspect_ratio(window, still, new_size=(WIDTH, HEIGHT_16_9)): '''Change the aspect ratio of the still displayed in window.Parameters ----------window : sg.Window Window containing the stillnew_size : 2-tuple New size of the stillReturns -------StillFrame Frame containing the resized image ''' resized_still = still.resize(new_size) window[’-IMAGE-’].update(data=resized_still.bytes()) return resized_stilldef save(still, path): '''Save still to a file. Parameters ----------still : StillFrame Still to savepath : string File nameReturns -------Boolean True if file saved with no errors ''' filename = Path(path) try:with open(filename, ’wb’) as file: file.write(still.bytes())saved = True except OSError:saved = False return saveddef next_timeout(delta): '''Return the moment in time right now + delta seconds from now. Parameters ----------delta : int Time in seconds until the next timeoutReturns -------datetime.datetime Moment in time of the next timeout ''' rightnow = datetime.now() return rightnow + timedelta(seconds=delta)def timeout_due(next_timeout): '''Return True if the next timeout is due. Parameters ----------next_timeout : datetime.datetimeReturns -------bool True if the next timeout is due ''' rightnow = datetime.now() return rightnow >= next_timeoutdef validate_delta(value): '''Check if value is an int within the proper range for a time delta. Parameters ----------value : int Time in seconds until the next timeoutReturns -------int Time in seconds until the next timeoutbool True if the argument is a valid time delta ''' isinteger = False try:isinteger = type(int(value)) is int except Exception:delta = DELTA delta = int(value) if isinteger else delta isvalid = MIN_DELTA <= delta <= MAX_DELTA delta = delta if isvalid else DELTA return delta, isinteger and isvalidLAYOUT = [[sg.Image(key=’-IMAGE-’)], [sg.Checkbox(’Correct aspect ratio’, key=’-RESIZE-’, enable_events=True), sg.Button(’Reload’, key=’-RELOAD-’), sg.Button(’Save’, key=’-SAVE-’), sg.Exit()], [sg.Checkbox(’Auto-reload every (seconds):’, key=’-AUTORELOAD-’, default=True), sg.Input(DELTA, key=’-DELTA-’, size=(3, 1), justification=’right’), sg.Button(’Set’, key=’-UPDATE_DELTA-’)]]def main(layout): '''Run event loop.''' window = sg.Window(’Spacestills’, layout, finalize=True) current_still = refresh(window) delta = DELTA next_reload_time = datetime.now() + timedelta(seconds=delta) while True:event, values = window.read(timeout=100)if event in (sg.WIN_CLOSED, ’Exit’): breakelif ((event == ’-RELOAD-’) or(values[’-AUTORELOAD-’] and timeout_due(next_reload_time))): current_still = refresh(window, values[’-RESIZE-’]) if values[’-AUTORELOAD-’]:next_reload_time = next_timeout(delta)elif event == ’-RESIZE-’: current_still = change_aspect_ratio(window, current_still, current_still.new_size())elif event == ’-SAVE-’: filename = sg.popup_get_file(’File name’, file_types=[(’PNG’, ’*.png’)], save_as=True,title=’Save image’, default_extension=’.png’) if filename:saved = save(current_still, filename)if not saved: sg.popup_ok(’Error while saving file:’, filename, title=’Error’)elif event == ’-UPDATE_DELTA-’: # The current cycle should complete at the already scheduled time. So # don’t update next_reload_time yet because it’ll be taken care of at the # next -AUTORELOAD- or -RELOAD- event. delta, valid = validate_delta(values[’-DELTA-’]) if not valid:window[’-DELTA-’].update(str(DELTA)) window.close() del windowif __name__ == ’__main__’: main(LAYOUT)
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