Use youtube-dl output template with extension parameter #50

[huseyz]

This solves #50.
When youtube-dl downloads the original file from youtube it's using the given output template to name the file.

Currently when podsync asks it to download a file and convert it to audio with an output template like /path/episodeip.mp3; this causes the original file to be downloaded as /path/episodeip.mp3. Which leads to ffmpeg using it as both input and output; this causes ffmpeg to exit immediately saying output file already exists.

As a result, all the files stay as webm video files named as [episodeid].mp3s. These can't be served by itunes etc.

To reproduce:

[server]
port = 80
hostname = "http://localhost"
data_dir = "./data/"

[tokens]
youtube = "[YOUTUBE_TOKEN]"

[feeds]
  [feeds.arsimet]
  url = "https://www.youtube.com/watch?v=gPKLRwSuXwQ&list=PLWXQ0iArMOp-a7rWy84upd7J3tgMv9eZo"
  page_size = 10
  update_period = "6h"
  quality = "high"
  format = "audio"

Example ffprobe GD5xkdt2vwY.mp3 -hide_banner output:

Input #0, matroska,webm, from 'GD5xkdt2vwY.mp3':
  Metadata:
    encoder         : google/video-file
  Duration: 00:17:19.82, start: -0.007000, bitrate: 119 kb/s
    Stream #0:0(eng): Audio: opus, 48000 Hz, stereo, fltp (default)

One can see the output saying "output file exists" by adding a line to ytdl.go:106

log.Infof("youtube-dl output: %s", output)

This PR changes causes podsync to use an output template [episode_id].%(ext)s which translates to [episode_id.mp3] or [episode_id.mp4] depending on the configuration. please note that youtube-dl will use mp3 or mp4 based on --format which is passed in function Download in ytdl.go:41

[mxpv]

Thank you for doing this! I have a few comments.

[huseyz]

I've made the changes you've asked for; calculation of the exact episode file path is still separated in multiple places. However unifying them in a proper way is beyond my go skills.

[mxpv]

Thank you!