Change file extension for audio file and resizing parameters during…

[jay3ss]

…crop of clip

The current version of youtube-dl appends webm to the frontier.mp4 file so that it's now frontier.mp4.webm, so I've updated the code in the example to reflect that (I couldn't find the parameters in youtube-dl's documentation to force the frontier.mp4 file name). Also, I changed the resizing parameters in the cropping of the video to match (as best as I could) the example posted to YouTube.

• I have provided code that clearly demonstrates the bug and that only works correctly when applying this fix
• I have added suitable tests demonstrating a fixed bug or new/changed feature to the test suite in tests/
• I have properly documented new or changed features in the documentation or in the docstrings
• I have properly explained unusual or unexpected code in the comments around it
• I have formatted my code using black -t py36

[coveralls]

Coverage remained the same at 67.597% when pulling f299440 on jay3ss:fix-dancing-knights-example-resizing-video into c4396fb on Zulko:master.

[tburrows13]

Hello, thanks for making this change. I've made a slight adjustment that I think will reduce confusion.

[jay3ss]

Thanks for the update, that's much clearer.