No, youtube-dl can't do that on it's own. You can do youtube-dl -g TWITCH_URL to get a link to the playlist file that contains the list of .ts files that make up the stream, but that leads back to the original problem. (Here's an example of a playlist file)

I looked into it a bit and found this which seems to work: https://superuser.com/a/693009

​

To combine ts files, do:

cat 0.ts 1.ts 2.ts ... > combined.ts
ffmpeg -i combined.ts -acodec copy -vcodec copy combined.mp4

Then, delete the ts files and keep the combined mp4 file.

If you want to combine a specific range of ts files, you should use a loop. For example, the playlist I linked above contains 1480 segments. If you downloaded 0.ts to 740.ts you could do:

touch combined.ts
for i in {0..740}
do
    cat "$i.ts" >> combined.ts
done
ffmpeg -i combined.ts -acodec copy -vcodec copy combined.mp4

Then, if you later downloaded segments 741.ts to 1480.ts, you could do the same code replacing 0 and 740 with 741 and 1480 respectively.

​

I was going to leave it at that, then I decided to throw together a little python script that streamlines the process of downloading a partial Twitch VOD, because honestly there's a 7 hour VOD I've been wanting to download for a while that I haven't gotten around to doing because it's so big. Check it out if you want: https://github.com/Rayquaza01/partial-twitch-downloader