Ubuntu – How to download a portion of a video with youtube-dl OR something else

Yes. From the youtube-dl man page:

--date DATE
          Download only videos uploaded in this date

--datebefore DATE
          Download only videos uploaded on or before this date (i.e.  inclusive)

--dateafter DATE
          Download only videos uploaded on or after this date (i.e.  inclusive)

Not stated there, but only hidden in the code, is that DATE is in the format YYYYMMDD or (now|today)[+-][0-9](day|week|month|year)(s)?, so for example the 17th August 2016 would be 20160817, and seven days ago would be now-7days or now-1week.

You can specify a range by using --datebefore and --dateafter together, so:

youtube-dl -i --dateafter 20160808 --datebefore 20160810 https://www.youtube.com/channel/CHANNEL

will download all videos from a channel uploaded between and including August 8th and August 10th 2016, and:

youtube-dl -i --dateafter now-1week https://www.youtube.com/playlist?list=PLAYLIST

will download all videos from a playlist uploaded in the past week.

The -i option prevents youtube-dl from exiting prematurely if some videos are unavailable.

Note youtube-dl will still say it is downloading each video even when it doesn't. For example:

[download] Downloading video 1 of 123
[youtube] xxxxxxxxxxx: Downloading webpage
[youtube] xxxxxxxxxxx: Downloading video info webpage
[youtube] xxxxxxxxxxx: Extracting video information
[youtube] xxxxxxxxxxx: Downloading MPD manifest
[download] 2016-08-07 upload date is not in range 2016-08-08 - 2016-08-10
[download] Downloading video 2 of 123
...

Playlist

youtube-dl -f FORMAT -ciw --output '%(title)s.%(ext)s' --playlist-start NUMBER-START --playlist-end NUMBER-END <url-of-playlist>  

...where <url-of-playlist> is replaced by the URL of the playlist, replace FORMAT with any available video format, for example 18, NUMBER-START is the number of the video in the playlist to start downloading first, and NUMBER-END is the number of the video in the playlist to download last.

Channel

If a channel has more than one playlist, click on the first playlist and download all the videos in the selected playlist using the above command. Then repeat for each playlist in the channel.

Explanation

-f, --format FORMAT
    video format code. The -F option (capital F) displays all available video  
    formats for a video link. Example: youtube-dl -F <url-of-video>

-c, --continue                   
    force resume of partially downloaded files

-i, --ignore-errors              
    continue on download errors, for example to skip unavailable videos  
    in a channel   

-w, --no-overwrites
    do not overwrite files 

Convert all the video titles to lowercase

youtube-dl -f FORMAT -ciw --output '%(title)s.%(ext)s' --playlist-start NUMBER-START --playlist-end NUMBER-END <url-of-playlist>     
find -type f -exec rename 'y/A-Z/a-z/' {} +

Explanation

--output '%(title)s.%(ext)s'  
    output file name(s) as the name of the video, followed by a dot character and the video's extension  

find -type f 
    Find all files.

y/source/destination/  
    Transliterate the characters in the pattern space which appear in source   
    to the corresponding character in destination.