True - However it is mostly the chipset and filtering quality that will affect image more so than the bitrates. Some drives provide much better picture quality even at 3 and 4 hour recordings, while others do poorly at anything past SP, due to the excessive filtering (softening) of the image or simply a poor quality codec
The recording times quoted are for standard SP quality level recording which is generally close to source quality. With the longer recording times, most DVD-recorders will lower resolution (image detail) and also sound quality (but this is much less noticeable than loss of image detail).
Lowering resolution will not necessarily mean lowering quality.
Here's why. If you are recording from tv tuner or from your VHS source, even the lower resolution will be enough. Originally, dvd recorders use 720x480 (or 704x480), which is quite enough if you are converting your MiniDV or S-VHS sources, but overkill for standard VHS and cable. even digital cable does not use that high of a resolution anyways nowadays
It's extra resolution wasted for nothing....... So recorders will use a mode called Half-D1, which is 352x480 (the vertical resolution remains the same). Half-D1 will NOT give you a worse picture than 720x480 for VHS sources or even for standard definition cable.....
The ADVANTAGE in lowering to Half-D1 is that you are doubling the efficiency of the bitrate.
XP and SP modes use 720x480.....
SP uses an average of 4.6mbit/s (number can vary depending on models, but it is usually between 4.4 and 4.8).
Now say you were recording at 2.4mbit/s using Half-D1.... It would be the equivalent of a recording done at 4.4mbit, since you have less data and the bitrate is used more efficiently. Now I have seen some DVD Recorders that show visible artifacts even at SP or lower bit rates and other recorders show virtually none and handle difficult scenes better.....the type of codec plays a big role.
Some DVD-recorders will allow you to record 8 hours of video on a disc but quality is not DVD quality of course but fairly comparable to VCD.
The recorded quality does depend on your broadcast source.
Yes it would be using MPEG-1 352x240 (which is part of the DVD specs as well), don't expect miracles - Don't even bother recording at that setting with motion scenes