A DVD is made up of mpg2 video, usually AC3 audio, one or more subtitle streams [in graphics format rather than text], that are bundled in .VOB files, each with a max size of ~1 GB. Machine instructions written in a non-human friendly scripting are included in .IFO files. Like Blu-Ray they essentially work with playlists, but there are also a couple of other methods to include more than one version of a video on a DVD disc. There's also the rarely used option to include Button Over Video, which gives you a menu button over the playing video.
DVD copy software puts a 1 to 1 copy of the files on a DVD disc onto a hard drive, where it can be left or burned to a fresh disc -- if you've got 2 DVD drives, & at least one of them is a DVD writer, you may be able to skip the hard drive copy. Some DVD copy software lets you copy just one title at a time, which is usually used to get the main video without the menus, added video features etc. A DVD Ripper has come to mean a video converter that can also read the DVD disc format -- as with CD ripping it used to mean copying the digital contents on a disc, with the benefit of no quality loss since it is an exact digital copy. Sometimes you'll still see the older definition in use.
Copying DVDs to a hard drive for permanent storage was Very popular because of its convenience, but that popularity's decreased since Blu-Ray & quality & content variety improvements with streaming. That does not however mean DVDs are dead -- they remain extremely popular. In the real world content owners & distributors are very stingy with quality, giving viewers the lowest quality that they feel they can get away with. Because of that the average DVD comes surprisingly close to, & may even exceed the quality of HD via streaming or satellite or cable to a HDTV. Many people convert HD video, e.g. from Blu-Ray, to smaller files they stream over their network or store on USB devices, using one of the very many media players boxes on the market -- for several reasons, including the limited bandwidth [bit rate] they often have to use, & a dislike for long encoding times, quality is [most?] often in the DVD range. And compared to most alternatives DVDs are extremely easy to use, & they're pretty durable.
The video on a DVD is usually anamorphic 720 x 480 or 576 that's displayed at 16:9 widescreen. In the US [NTSC spec] the 24 fps [or 23.976] of film is usually upped to the spec's required 29.976 fps through the use of flags embedded in the file. Those flags tell the player what frames to repeat to achieve the required fps -- it's called 3 2 pull down. As possible you want to stick with the original 24 fps rather than store a bunch of identical frames at 29.976 fps -- it adds to the file size with no visual improvements. That's not always easy however, so consider it a goal rather than a must do.
Because it uses standard definition [rather than HD] broadcast formats, DVD video does not use square pixels. What happens on your PC is if you play DVD video, or often any video at DVD frame sizes, the player will either compensate & alter the displayed frame size, or not. If you use a DVD player app like PowerDVD, the DVD video frame will roughly match the aspect ratio you see on your TV -- a player that does not compensate will show the frame as-is, with an incorrect aspect ratio, & everything will be distorted. OTOH if you have regular, square pixel video at DVD frame size, some software will alter the frame anyway, & again you get distortion. Converting square to non-square & the reverse exactly gets complicated -- considering 720 width non-square to equal 640 width square is usually close enough, but only if it's not anamorphic.
Most of the software you'd use to convert DVD video into something else will handle maintaining the DVD's intended aspect ratio for you -- you just need to be aware of the potential issues so you can check the output & change the software settings if/as needed. If you're taking a more hands-on approach, the easiest method I've found is to play the DVD video in something like PowerDVD, use the app's screen shot feature, then open the image you captured in image editing software. You can see the existing frame dimensions, or change the size maintaining aspect ratio, and you can get cropped dimensions too removing any letterboxing. Bear in mind that some encoders require frame dimensions that are divisible by 4 or 8 or 16 in case once you come up with a target desired frame size it won't work -- it's often a matter of getting as close to your desired frame size as possible, rather than always using the size you come up with as-is.
Another issue that can come up because DVDs use SD broadcast specs is color -- specifically the color range between pure black & pure white. This is an area where your mileage can vary tremendously based on your playback & display hardware, including your TV(s). Over the air analog broadcast uses a reduced color range because it was required with the old tech & thus built into the specs. It's long been possible for TVs to display the full, or a larger color range, but not every TV includes that capability. DVD, Blu-Ray, & media players may or may not send out a signal to your TV that includes the full color range. Whether a HDTV can display the full color range also varies, and the same with PC/laptop displays. PC/laptop software &/or hardware drivers vary in what they'll output & in what they'll let you set. And you might find that software players [Windows or Android] already expand or alter the color range of everything they play.
So, what that all means to you is that you **might** see some benefit if when you re-encode DVD video [assuming you do re-encode that video], you also increase the color range of that video. It's far from guaranteed, & it can depend on the DVD video itself -- it depends on how the original footage was processed, & how many times it was processed, to get it on the DVD in the 1st place.
One way to accomplish it is to use a video editor that includes the feature to expand the color range to re-encode your video. Another way is to use DGIndex [which also removes pull down so you can get 24 fps] with AviSynth to get the video into VirtualDub, then encode an intermediate file using a codec like PicVideo mjpg, which can automatically expand the color range, & re-encode that to your final format. You could also do a bit of research, find the best way to expand the range with AviSynth, & output using the x264 VFW encoder -- that lets you skip the intermediate file, at the expense of learning how to expand the color range in AviSynth. AviSynth uses scripts -- using it to import a DGIndex file is trivial, but more than that can get involved. And again I stress it might not make a bit of difference to what you see watching the video, or it might make what can seem a night & day improvement.
Captioning &/or subtitles are often included on a video DVD. Closed Captioning can be embedded in mpg2 video rather easily, & ccextractor can get it out & into a text file if you want. CC is on the decline however as you can only buy HDTVs in the US, they're required to have HDMI, & you cannot pass CC to an HDTV via HDMI. Nor can most software play CC, & a great many DVD authoring apps cannot add the necessary settings to a DVD to enable CC display on a PC regardless the player.
DVD & Blu-Ray subtitles aren't text but pictures of text. The disc includes the outline of the characters, & the player colors those outlines depending on what the player is set to, & depending on the instructions included on the disc. There are apps to change subtitle colors & timing, there's software like BDSup2Sub that will resize subtitles, & there's software like SubtitleEdit to OCR them into text files with timings. There are apps to edit subtitle text files, changing timing & things like line breaks. And there's software to render text subs into the graphics type on discs. It's possible to embed graphics subtitles in MKV & .MP4 files, but the players that will display those subs are few. Text subs in the .srt format, in the same folder with & a name matching the video file, can be displayed by many more players, including many Android players.
It is possible to edit DVD & Blu-Ray discs, but more often I think they're either re-made or simply have the main title extracted. Re-making a disc lets you have menus but leave out the stuff you don't want -- if you just strip out something, for example the different language audio tracks, the menu choices for that stuff remains. PgcDemux will strip the separate audio, video, & subtitle files from a DVD -- there are several Tsmuxer front ends, e.g. the old Blu-Rip, that'll do the same for Blu-Ray discs -- neither will work with DRM. The old DVD Shrink can be useful to trim the end credits from a movie [you'd be surprised how much that can effect the final file size]. It can also copy a DVD title combining several 1 GB .VOB files into a single .VOB, & that single file can often be used with video converters that cannot read DVDs.
DVD Shrink's original purpose was to reduce the size of a DVD video file(s) so the contents of a dual layer DVD would fit on a then much cheaper single layer blank. Dual layer blanks aren't expensive nowadays, & if file size is a concern, there are more efficient video formats, like AVC that are more widely accepted today than mpg2. Long story short, while you'll still see software & people make claims about putting dual layer DVDs on a single layer disc, it's a relic from the past that's best forgotten. It's a solution without a purpose.
The last bit of advice I'll put down here today is to use common sense, research, & test the ways to store & play video that you're considering. There is No One best way to do this stuff, & because lots of people don't include those 3 things, they wind up spending more time, effort, &/or cash to get poorer results than they would otherwise. I just bought 50, 25 GB BD blanks for $20 -- that's a lot cheaper per GB than any hard drive, even remans, so if cost is a big concern, don't store video on hard drives or USB sticks. Streaming video takes up bandwidth. That means issues if you're streaming on-line video or from one device to another via your home network. Re-encoding video to standard broadcast [i.e. DVD] frame sizes is fairly quick -- encoding to HD H.264 [AVC] or H.265 etc. is usually painfully slow at good quality levels. At the very least make sure it's worth it -- every re-encode will lose quality -- since it's often easier to figure out how to play the video you've already got.
