Question about bitrate, spikes and Bitrate viewer

[sasuweh]

I am converting some VHS>DV captures in CCE, and I am noticing that there are always a few bitrate spikes that go above the maximum allowed. I use CCE VBR, and no matter what I set my maximum bitrate to, it tends to have several spikes somewhere that go over, just a few, sometimes only 1 or 2, but still, there are spikes. Because of that, I am finding I need to encode at a lower average bitrate and set my maximum lower than I want, just to leave it room to spike and still be within DVD spec.

I use Bitrate Viewer to analyze the .m2v files output by CCE, and there are 3 different scan modes - Second based, GOP based, and GOP enhanced. The spikes always show up in the second-based scan mode, but in GOP based and GOP enhanced, it is always evened out with no spikes, and the maximum is much much closer to the max I specified. I am wondering which method I should be scanning in to get reliable results? I don't want to worry about the bitrate being so close to the limit that playback could become a problem. So which should I be paying attention to - second-based or GOP based?

Example:

Second based
Average - 7482
Peak - 9220

GOP based
Average - 7482
Peak - 8423

GOP enhanced
Average - 7482
Peak - 8423


Notice how much higher the peak is in Second based mode. Once I add the AC3 audio it will be pretty close to max. If it wasn't for those couple spikes, I could increase the average and peak bitrates. But when I do that, the peaks are way to high in second-based mode.

[poisondeathray]

Neither. Technically you need a buffer analyser

What you are looking at is instananeous bitrates per unit time, but this isn't what is important. What's important is how full the buffer is at that point in time, and how much data is incoming. It's an input vs output balance equation. If you have a buffer underrun, some player will stutter and skip

The spikes show in second based mode, because a second in duration will have 29.97 frames per second, but a single NTSC GOP will only have 18 frames max (ie. less than 1 second, thus less data, so a smaller "spike")

It's a good idea to leave some slack space - be more cautious, because some cheap DVD players don't even abide by the rules (they can skip/studder even at medium-high bitates even below 9Mb/s when it's clearly stated in the DVD specs that ALL PLAYERS MUST be able to decode 9.8Mb/s)

[manono]

Here's a slightly different opinion. If the max allowable bitrate is 10080 kbps including audio, video, subs, and overhead, then I don't see how you're very close to the max at all with a max bitrate set in CCE of 8500 (?). Even if you're using DD 5.1 audio at 448. I set my maxes in CCE at 9500. Haven't you already been told to author using Muxman, at least as a test? If it authors without incident, you can be assured it's within spec. And I wouldn't pay any attention at all to the second based one.

[sasuweh]

Okay, thanks for the advice. I'm using muxman, and it authored the dvd fine with DD 2.0 @384. So I'm not going to worry about it then.