TwitchDown is a Perl script for downloading twitch.tv VODs (Video-On-Demand),
similar to TwitchVODDownloader tool:
http://www.twitchvods.com/download/
Main difference is that TwitchVODDownloader starts ffmpeg for direct converting
video from remote URL, while TwitchDown first downloads all segments locally and
then starts ffmpeg to combine them. This requires disk space twice as video
would take, but ensures that all segments are downloaded correctly: with remote
URL some segments may be silently skipped due to connectivity issues during
download.

Other differences from TwitchVODDownloader:
* No GUI.
* No authorization.
* Instead of end time, the total length can be specified.
* Warnings about muted segments and video discontinuities.

Usage:
	perl twitchdown.pl {URL|VideoID} {FileName} [Options]

Arguments:
	URL              URL to the requested video at twitch.tv.
	VideoID          ID of the video.
	FileName         Name of the local file to save the video.

Options:
	--start=TIME     Download video starting from the specified timestamp.
	--end=TIME       Download video up to the specified timestamp.
	--len=TIME       Download video only the specified length of time.

	Supported TIME formats:
	h:mm:ss
	h:mm       (seconds = 0)
	5h, 5m, 5s (5 hours, 5 minutes, or 5 seconds)

Examples:
	perl twitchdown.pl https://www.twitch.tv/squirrel/v/63949920 e:\Video\Squirrel-SNT.mp4
	perl twitchdown.pl 63949920 e:\Video\Squirrel-SNT-cut.mp4 --start=1:15:00 --len=2:00:00

Hardcoded options:
	$NUM_THREADS     Number of threads to use for downloading video segments.
	$NUM_RETRIES     Number of retries when download fails before giving up.
	$data_dir        Path for storing temporary data (video segments).
	$ffmpeg_exe      Path to ffmpeg executable file.