Forum archive - Alright, what IS the big deal with variable bit rate recording?

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Alright, what IS the big deal with variable bit rate recording?

ministry88 posted 2009 Jul 01 15:41

First off, I've done a lot of reading on this forum about DVD recorders with customizable bit rate options. But I still, in my experience, can't tell the frickin' difference between a DVD-R I burn with variable bit rate (to maximize the bit rate) and one burned in plain vanilla SP mode on the same machine (a Pioneer DVR-340H). I've tried these DVD-Rs on many displays, from low-res CRT TVs to high-end high-res displays like plasma, LCD, and DLP front projection. Again, I can't see any video difference in noise or compression. Often the difference between a DVD-R in SP mode or one in flex mode is only .5G or 1G max. And strangely, I've noticed there is a strong strobing/flickering issue on my computer LCD display on DVD-Rs burned on flex mode, but this is reduced (or eliminated) on DVD-Rs burned in SP mode! The flicker vanishes on any other display, but it's strange. So what do people think of this flex bit rate option? If I've learned anything in video, it's there is no one-size-fits-all solution.

edDV posted 2009 Jul 01 15:50

VBR is supposed to allocate more bit rate to higher action scenes and less to low motion. This can be compromised by noisy source which gets detected as all high motion. Groups of streams can share variable bit rate though a process known as "statistical multiplexing". This allows a fast action scene to draw bit rate from lower motion companion channels. The group maintains a constant bit rate for transmission. This can be used to carry more sub channels in a fixed rate transponder or QAM cable channel. Again high source signal to noise is important.

ministry88 posted 2009 Jul 01 16:05

eddv- what exactly do you mean "high source signal to noise is important"? Always wondered what that meant. So are you saying that in noisy sources the VBR may not do much because it fools the VBR into thinking it's a high-motion scene? But wouldn't that be a good thing because then the video is ALWAYS getting maximum bitrate?

edDV posted 2009 Jul 01 16:22

ministry88 : So are you saying that in noisy sources the VBR may not do much because it fools the VBR into thinking it's a high-motion scene? That is what I meant. ministry88 : But wouldn't that be a good thing because then the video is ALWAYS getting maximum bitrate? No because VBR specifies an average bit rate and increases or decreases around that. If there is no low noise, low motion content then everything normalizes to average. PS: Signal to noise (SNR or S/R) indicates absence of random noise. Higher is better. VHS best case is ~35dB where DV is above 60dB.

jjeff posted 2009 Jul 01 16:26

If your size difference is only .5G (say 3.6G vs 4.1G) I doubt you'd be able to see much difference between the two, except maybe in scenes that would require more bitrate. Such as falling confetti, strobe lights, running water, etc. Where I really like Flexible Record is on a Panasonic where something is longer than 2hrs. If you're forced to use LP you'll probably notice the presents of macoblocking, if you can use FR and set it for anything under 3hrs/disc you'll notice the macroblocking decreased significantly. It would sure be nice if Panasonic had a 2 1/2 and 3hr speed, but unfortunately they don't, which is where FR really comes in handy. If your source material is less than 2hrs then by all means use SP, to me FR is best to use between SP and about 3hrs/disc(on a Panasonic).

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