[BUG] KeyError 'start' when getting captions from a video

I keep getting KeyError: 'start' when I try to get a caption from a video in a playlist.

To Reproduce Here is the code I am trying to test:

import pytube
from pytube import Playlist, YouTube

url = "https://www.youtube.com/watch?v=vKA4w2O61Xo&list=PLkahZjV5wKe8WFEwvs69V7JO-Cx57rZ8W"
p = Playlist(url)

for v in p.videos[:3]:
    print("trying to get captions for:", v.title)
    print(v.captions["a.en"].generate_srt_captions())

This code used to print the caption before updating pytube, but now it breaks with the following trace:

KeyError                                  Traceback (most recent call last)
~\test_pytube.py in <module>
     10 for v in p.videos[:3]:
     11     print("trying to get captions for:", v.title)
---> 12     print(v.captions["a.en"].generate_srt_captions())

~\AppData\Roaming\Python\Python38\site-packages\pytube\captions.py in generate_srt_captions(s
elf)
     49         recompiles them into the "SubRip Subtitle" format.
     50         """
---> 51         return self.xml_caption_to_srt(self.xml_captions)
     52
     53     @staticmethod

~\AppData\Roaming\Python\Python38\site-packages\pytube\captions.py in xml_caption_to_srt(self
, xml_captions)
     81             except KeyError:
     82                 duration = 0.0
---> 83             start = float(child.attrib["start"])
     84             end = start + duration
     85             sequence_number = i + 1  # convert from 0-indexed to 1.

KeyError: 'start'

System information Please provide the following information:

• Python version: Python 3.8.5
• Pytube version: 11.0.0
• Command used to install pytube: pip install -U pytube

[maksimbolonkin]

Apparently YouTube changed their captions format.

Here’s my version of the function for the function in captions.py:

def xml_caption_to_srt(self, xml_captions: str) -> str:
      """Convert xml caption tracks to "SubRip Subtitle (srt)".

      :param str xml_captions:
          XML formatted caption tracks.
      """
      segments = []
      root = ElementTree.fromstring(xml_captions)[1]
      i=0
      for child in list(root):
          if child.tag == 'p':
              caption = ''
              if len(list(child))==0:
                  continue
              for s in list(child):
                  if s.tag == 's':
                      caption += ' ' + s.text
              caption = unescape(caption.replace("\n", " ").replace("  ", " "),)
              try:
                  duration = float(child.attrib["d"])/1000.0
              except KeyError:
                  duration = 0.0
              start = float(child.attrib["t"])/1000.0
              end = start + duration
              sequence_number = i + 1  # convert from 0-indexed to 1.
              line = "{seq}\n{start} --> {end}\n{text}\n".format(
                  seq=sequence_number,
                  start=self.float_to_srt_time_format(start),
                  end=self.float_to_srt_time_format(end),
                  text=caption,
              )
              segments.append(line)
              i += 1
      return "\n".join(segments).strip()

[geomags3]

@maksimbolonkin I changed a bit your code, so now it works for me as well 👌 The issue I’ve found was caused by the fact that some captions are located inside of <p> tag

    def xml_caption_to_srt(self, xml_captions: str) -> str:
        """Convert xml caption tracks to "SubRip Subtitle (srt)".

        :param str xml_captions:
        XML formatted caption tracks.
        """
        segments = []
        root = ElementTree.fromstring(xml_captions)
        i=0
        for child in list(root.iter("body"))[0]:
            if child.tag == 'p':
                caption = ''
                if len(list(child))==0:
                    # instead of 'continue'
                    caption = child.text
                for s in list(child):
                    if s.tag == 's':
                        caption += ' ' + s.text
                caption = unescape(caption.replace("\n", " ").replace("  ", " "),)
                try:
                    duration = float(child.attrib["d"])/1000.0
                except KeyError:
                    duration = 0.0
                start = float(child.attrib["t"])/1000.0
                end = start + duration
                sequence_number = i + 1  # convert from 0-indexed to 1.
                line = "{seq}\n{start} --> {end}\n{text}\n".format(
                    seq=sequence_number,
                    start=self.float_to_srt_time_format(start),
                    end=self.float_to_srt_time_format(end),
                    text=caption,
                )
                segments.append(line)
                i += 1
        return "\n".join(segments).strip()

So to fix this bug we can just replace xml_caption_to_srt inside of pytube/captions.py/Caption class with current code. Hope it’s gonna work for everyone 👍