CBR not constant???

[Kevin Henry]

Encoded Tomb Raider from DivX to SVCD.

TMP - Set the bitrate to 2842 CBR.

However, playback in PowerDVD on computer with 'information' on gives me a bitrate of 2.4Mbit that spikes every few seconds to 5+.

When I burn the mpg, it's real jerky on the DVD standalone - picture and audio.

I guess it's cos of the spiking bitrate - but it's supposed to be CBR!

Suggestions???

[ya_jai]

It might be your player cannot handle this high bitrate, just my 2 cents.

[adam]

Its jerky because you did not make a SVCD you made an xSVCD, a non-standard SVCD. The max total bitrate a SVCD can have is 2778kbits. You are most likely well over this if you used 2842 just for video, because you still have to take audio and overhead into account.

As for CBR not being constant, well you have to look at how mpeg encoding works. The bitrate you set only specifies how many bits the encoder allocates to each second of video, essentially to each GOP. Even at CBR that bitrate still has to be divided up to each frame within that one second and the amount each frame gets depends on its priority. So CBR is really like a bunch of VBR encodes every second. The bitrate fluctuates from frame to frame but always averages out to your specified amount every second, whereas in true VBR encoding the bitrate not only fluctuates from frame to frame, but also from second to second as long as all bitrate averages out to your specified setting.

Also PowerDVD is probably not the most accurate bitrate calculator, there are programs specifically designed for this. Try Telco's BitrateViewer. Its still not totally accurate but its pretty good.

In the meantime, lower your bitrate!

[Kevin Henry]

thanks adam...

...so, if we cant use bitrates greater than 2520 for SVCD, how do we get primo quality? I have starwars2 that is PERFECT quality, downloaded as svcd???

time to break out cce?

[BJ_M]

the one you downloaded was prob not a conversion from divx to svcd as you are doing .. converting from one lossy format to another -- well something going to be lost ..

Telco's BitrateViewer is one great app -- the full version allows you to change the headers including the aspect ratio without re-encoding .. it reports the gop structure on muxed files wrong though - and bit rate a bit off also on program streams - but on raw streams it is very good ..

cce will not give substancially better quality than tmpgenc on your conversion from divx to svcd .. though if you set the bit rate to 2842 CBR , it shouldnt spike to 5000 (except at the end were tmpgenc has a habit of doing so) .. adam is right , you didnt make a true svcd ..
also at that low a bit rate you may be better off with VBR anyway - unless you dont care about prob needing 3-4 cd's instead of two ..