RDK45 wrote:If all of this is correct, then what is HD? Is it restricted to folks using Blu-ray disks?
Your central question is 'what is HD', and the simple answer is that it is video which has a frame size higher than 720 x 480 (NTSC) or 720 x 576 (PAL). Usually, though not necessarily, HD video will also have a bitrate much higher than 10,000 kbps -- though more recent HD codecs can produce extremely high quality video with much lower bitrates...
The problem, I think, is that in your mind you are equating high quality with high definition. That is a logical correlation, but in video terms it can lead to faulty conclusions. What you need to keep in mind is the distinction between standard definition and high definition (and now even Ultra High Definition [UHD]) video. For many years, standard definition was the best high quality video we could achieve, and by international standards, the maximum frame size was 720 x 480/576 and the combined maximum bitrate (video AND audio) was 10,000 kbps -- though in practical terms some stand-alone video players, and indeed some NLE video editors, had difficulty with video bitrates above 8000 kbps. So in in effect 8000 kbps became the accepted highest bitrate which would give you the best quality standard definition video on a DVD.
Bitrate not only affects quality -- it also affects the size of a video clip. The higher the bitrate, the bigger a clip will be. So with a standard definition single layer DVD, which can hold 4.3 GB of video, if you were using video at 8000 kbps, then you could only fit about one hour of that video on the DVD (or a little more if you used a highly compressed audio format like Dolby for the audio track). To repeat, in standard definition terms, this would give you the best quality video you could hope to achieve in the standard definition world. You could still get pretty good quality -- and the human eye might not even notice the difference -- if you lowered the video bitrate to, say, 6000 kbps, and this would allow you to burn 90 minutes of video to a single layer DVD (or a bit more by using Dolby audio). Lowering the bitrate still further to 4000 kbps would allow 2 hours to be burned to a DVD, but the quality would be no better than that you would get on one of the old VHS video tapes...
And then came the era of high definition video cameras which use not only higher bitrates (which as already noted gives you better quality the higher the bitrate goes) but also increased the frame size first to 1280 x 720, then 1440 x 1080 and 1920 x 1080. And of course having a much bigger frame allowed much greater numbers of pixels to be in a frame, making the video much clearer or detailed ("higher definition") than standard definition video. And now of course we have UHD video using even larger frame sizes and much higher bitrates.
None of this is to say that standard definition video cannot be good and high quality within its own standard. It's just that it is not as good to the human eye as high definition video...
And is it "restricted to folks using Blu-Ray disks"? In a strict sense, yes. As we have already indicated, you can in fact burn HD video, using the HD AVCHD H.264 codec to what otherwise would have been a standard definition DVD blank disk. This is the hybrid or AVCHD disc. And if using the maximum bitrate for such disks of 18,000 kbps, you can only squeeze a maximum of 25 - 30 minutes of HD onto a single layer DVD. And the other limitation is that the disk will only play on a Blu-Ray player rated to play AVCHD discs (though most can).
Many of us, though, have in a sense moved beyond disks. I personally have a Blu-Ray recorder and two Blu-Ray players, but I haven't burnt a disc of any kind for more than two years. These days I render my high definition projects to a new HD video (either AVCHD or transport stream Blu-Ray compatible mpeg-2) and simply copy it to a USB stick drive or external USB hard disc. Both these types of drives have dropped enormously in price in recent years. And both can be either plugged directly into modern HDTVs or into a Blu-Ray player connected to a HDTV. More recently, another video format, HEVC which uses the H.265 codec, is also becoming popular, but it requires high end computers with CPUs no more than two or three years old, to edit and produce.
Admittedly, when distributing your video masterpieces to family and friends, not everyone will necessarily have the equipment to play Blu-Ray discs or high definition video on a USB stick or hard drive, and you will have to down-convert your video from a HD camera to standard definition DVD. For the people watching such DVDs on their older DVD players and TVs, the video will still look very high quality. It's just that, for you, it will not be the original high definition!
