如何用Python监控NASA TV直播画面

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演示地址：

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 frame        original : PIL.Image            Original frame with wchich the instance is initialized, cached in case of            resizing to the original size        Methods    -------        bytes : Return the raw bytes        resize : Resize the screenshot        new_size : Calculate new aspect ratio    """    def __init__(self, image):        """Convert the image to PNG and cache the converted original.        Parameters        ----------            image : PIL.Image                Image to store        """        self.image = image        self._topng()        self.original = self.image    def _topng(self):        """Convert image format of frame to PNG.        Returns        -------            StillFrame                Frame 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_image        return self    def bytes(self):        """Return raw bytes of a frame image.                Returns        -------            bytes                Byte 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-tuple                New size        """        size = self.image.size        original_size = self.original.size        new_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-tuple                New size        Returns        -------            StillFrame                Frame 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 size        Returns    -------        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 from        Returns    -------        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 to        feed : string            Feed URL        Returns    -------        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 still        new_size : 2-tuple            New size of the still        Returns    -------        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 save        path : string            File name        Returns    -------        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 timeout        Returns    -------        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.datetime        Returns    -------        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 timeout        Returns    -------        int            Time in seconds until the next timeout        bool            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'):            break        elif ((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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