Use audio_codec option even if audio is given as filename

[zalgo3]

moviepy.video.VideoClip.write_videofile ignores audio_codec when audio is a file name. I have fixed it in this PR.

• I have provided code that clearly demonstrates the bug and that only works correctly when applying this fix
  • moviepy.video.VideoClip.write_videofile("output.mp4", audio="input.wav", fps=60, audio_codec="aac") have run ffmpeg with -acodec copy. With this PR, it will run the command with -acodec aac.
• 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

[coveralls]

Coverage: 83.988% (-0.8%) from 84.751% when pulling e7cbfd3 on zalgo3:use-audio-codec-for-existing-audiofile into 86fd511 on Zulko:master.

[keikoro]

Thanks for your PR.

I think I might nab just the black formatting fixes for now to prevent our checks from failing (even though they don't even fail consistently...).

[mgaitan]

why not default to "copy" directly here ?

[zalgo3]

Thanks for your question! The default value of audio_codec in VideoClip.write_videofile is None, so I also adapted FFMPEG_VideoWriter to that.

moviepy/moviepy/video/VideoClip.py

Line 209 in e7cbfd3

audio_codec=None,

This pull request intends that in VideoClip.write_videofile, if a filename is given for the audio argument and a codec name is given for audio_codec, then it will be encoded according to that codec, but If audio_codec=None, I thought it would be better to have it copy as before.