This got 'broken' after moving to my fork of pymp4 because my fork has commits by TrueDread that add support for the vttc, payl, and sttg boxes, therefore they no longer contain `data` fields but rather specifically parsed fields. I also no longer need to parse the data stream of vttc boxes, as they are already parsed as `children`.
Negative size values are not allowed by the spec basically anywhere in the document. Some services seem to accidentally specify a negative value which puts pycaption on a fritz.
The new system now downloads and decrypts segments individually instead of downloading all segments, merging them, and then decrypting. Overall the download system now acts more like a normal player.
This fixes#23 as the new HLS download system detects changes in keys and init segments as segments are downloaded. DASH still only supports one period, and one period only, but hopefully I can change that in the future.
Downloading code is now also moved from the Track classes to the manifest classes. Download progress is now also actually helpful for segmented downloads (all HLS, and most DASH streams). It uses TQDM to show a progress bar based on how many segments it needs to download, and how fast it downloads them.
There's only one down side currently. Downloading of segmented videos no longer have the benefit of aria2c's -j parameter. Where it can download n URLs concurrently. Aria2c is still used but only -x and -s is going to make a difference.
In the future I will make HLS and DASH download in a multi-threaded way, sort of a manual version of -j.
This happened because the WEBVTT header was segmented and appended to each other without enough newline separation so pycaption thought it was an actual caption and to be kept.
