Cheap DVD discs do not have the quality dye layer that the premium brands do and thus do not create reliable DVDs. Burning a video DVD is much more demanding than burning a data DVD, data CD or music CD.
This post by Bengt Wärleby in this topic discusses video DVD quality: DVD quality
Follow this workflow to help assure the best qualty video DVD:
Once you have the project as you want it save it as a disk image via the File ➙ Save as Disk Image menu option. This will separate the encoding process from the burn process.
To check the encoding mount the disk image, launch DVD Player and play it. If it plays OK with DVD Player the encoding is good.
Then burn to disk with Disk Utility or Toast at the slowest speed available (2x-4x) to assure the best burn quality. Always use top quality media: Verbatim, Maxell or Taiyo Yuden DVD-R are the most recommended in these forums.
For more on DVD disk quality: Blank DVD Media Quality Review