The following is a "guide" for getting various video formats into an editing application, as those programs don't accept every format and codec that is out there, thus a transcoding (change format and codec) process has to be gone through first.
Every format gets its own post.
A. Get footage from a video DVD into an editing application
B. Get footage from an .avi file, using the Divx or Xvid codec, into an editing application
C. Get footage from an .mkv file, using the H264 or another MPEG-4 codec, into an editing application
D. Get footage from an .mp4 file, using the H264 or another MPEG-4 codec, into an editing application
E. Get footage from an .mov file, using the H264 codec, into an editing application
A. Get footage from a video DVD into an editing application
Every format gets its own post.
A. Get footage from a video DVD into an editing application
B. Get footage from an .avi file, using the Divx or Xvid codec, into an editing application
C. Get footage from an .mkv file, using the H264 or another MPEG-4 codec, into an editing application
D. Get footage from an .mp4 file, using the H264 or another MPEG-4 codec, into an editing application
E. Get footage from an .mov file, using the H264 codec, into an editing application
A. Get footage from a video DVD into an editing application
1. Get the footage from DVD
2. Transcode the footage to an editing friendly format
2. Transcode the footage to an editing friendly format
1. Get the footage from DVD - copied and pasted from How to backup/copy/rip video DVDs to your HDD and transcode them to another format.
As commercial video DVDs use a copy protection scheme called CSS (Content Scramble System), additional software is needed to copy the content of a video DVD to your HDD, which is called "ripping". There are several applications to accomplish this.
1.1. MacTheRipper 2.6.6 (free)
Insert the video DVD into your DVD drive and open MacTheRipper and click the GO button, after which you can select the place you want the video DVD's content saved to.
As this version of MTR is quite old, it will not read many modern DVDs.
As this version of MTR is quite old, it will not read many modern DVDs.
1.3. Fairmount (free) - needs VLC 32-bit to decrypt the CSS (thanks to Satori for that information)
1.4. Mac DVDRipper Pro (9.95 USD)
Insert the video DVD and select a destination folder, then press the RIP button.
2. Transcode the footage to an editing friendly format
As Handbrake does not offer any options to transcode into an editing friendly format (see here for details), one needs to use MPEG Streamclip to have more transcoding options like the .mov container format and a variety of codecs (DV, Apple Intermediate Codec, ProRes, ...), which makes buying (19.99 USD) and installing the QuickTime MPEG-2 Playback Component a necessity, in order to open ripped video DVDs in MPEG Streamclip.
2.0 Opening a ripped video DVD in MPEG Streamclip
2.0.1 MPEG Streamclip > File > Open DVD (SHIFT+CMD+O)

2.0.2 Browse to the VIDEO_TS folder of your choice and click Select

2.0.3 Many video DVDs come with several titles (menu, trailers, extras, film, ...), thus make sure you select the correct title, which might involve some trial and error though.

2.0.4 A successful opened video DVD looks like this:

2.1 Transcode the MPEG-2 encoded video for iMovie, Final Cut Express and Final Cut Pro - Apple Intermediate Codec (AIC)
2.1.1 MPEG Streamclip > File > Export to QuickTime ... (CMD+E)

2.1.2 Export Settings for the Apple Intermediate Codec for PAL DVDs
Choose the AIC for Compression (video) and Uncompressed for Sound.
If you have an NTSC DVD, select DV-NTSC or Unscaled.

Choose the AIC for Compression (video) and Uncompressed for Sound.
If you have an NTSC DVD, select DV-NTSC or Unscaled.
2.2 Transcode the MPEG-2 encoded video for Avid Media Composer
2.2.1 MPEG Streamclip > File > Export to QuickTime ... (CMD+E) - like 2.1.1
2.2.2 Either choose Apple DV PAL/NTSC or Avid DV PAL/NTS as video compression. The sound stays uncompressed.
2.3 Transcode the MPEG-2 encoded video for Adobe Premiere Pro