Bitrate Calc Question?

[gwoiler]

The Bitrate Calculator just lists one bitrate setting. How should I relate to that setting when encoding with VBR? I know I have read posts in here where people say to use such and such a setting... but what is the rationale in choosing your minimum... average... and MAX bitrates in TMPG?

Thanks,
glenn

[adam]

A bitrate calculator only calculates one bitrate setting, that is the average bitrate. When using multipass VBR encoding, set your average bitrate to this. You would also use this setting if encoding CBR, because naturally if the bitrate is constant (more or less) then that constant level would also be equal to its average.

As for max and min settings, basically the larger the interval between them the better. So you'd want your minimum to be equal to the lowest amount of bitrate you think any given scene will use. I always set this to 0, which is basically just automatic. As for max you should use either the highest amount allowed in the standard (don't forget to factor in audio and other overhead) or the highest amount your dvd player can accept.

So for instance, if you were encoding to DVD with one audio track at 448kbits you'd take 10.08mbits and subtract 448kbits to get your max setting. You should also allow yourself a little extra room just in case.

Finally, these are theoretical suggestions. Using a higher min setting or a lower max setting theoritically only decreases quality without gaining you anything. Some people have reported that TMPGenc's bitrate allocation is such that it helps to have an even max/min relative to your average. In other words, if your average is 4mbits you should set your min to 2mbits and your max to 6mbits, or 1mbit and 7mbits, etc... Keep it even on both sides. Personally, I disagree but you should experiment for yourself.

[gwoiler]

Thanks... I will follow your instructions. I have always used TMPG for encoding. I feel I should try BBMpeg. I read every once in a while that TMPG is not spec. I have noticed that when I am putting 6 hours to a DVD at 352x240 (talking heads) that it does not play correctly in some cheap players. I wanted to see if BBMpeg played in those troubled players. I don't normally cram that much video to a DVD... but this looked just as good if not better than video recorded on a vhs at the 6 hour speed. I wonder why TMPG can't be made to encode spec legal mpeg's.

Thanks for your reply,
Glenn

[adam]

Get ready for a long wait. BBmpeg does seem to produce compliant output, as far as I can tell, and the quality is actually pretty decent, but it is horribly slow.

TMPGenc has its quirks but if you overcompensate for them you should get very good compatibility. For 352x240 footage, make sure you set DC precision to 8, aspect ratio to 4:3, and whenever using TMPGenc its best to set it to closed GOPs. For any other encoder use open GOPs.

[cona812]

when using TMPGenc set the "number of P pictures in GOP" on 3. Some players have problems with longer GOPs (TMPGenc standard is 5 P-pictures per GOP).

[gwoiler]

I read the F.A.Q. on encoding high quality with TMPG on this web site, when it was DVDRHELP.com and from all the tips, I have always set the max number of frames per gop to 12 and only 1 - B frame per sequence. I have never tried anything other, so I am not sure the diference.

Number of B pictures - 1 (use a value between 0 and 3)

B-pictures are based on past and future I and P-pictures. They provide the best compression but, as with P-pictures, have problems when the image changes too much. Also, bear in mind that B-pictures cannot be based on other B-pictures, so don't use too many in a row or the image quality will suffer, especially if there are any cuts or sudden changes. B-pictures also take longer to encode, because they must search more frames for matching blocks. If you're using a high average bitrate (above 6000 Kb/s or so), you can use I and P-pictures only.

The quality looks the same as DVD Studio Pro that I use at work. TMPG encodes much faster though. MACs are still catching up as far as horse power goes. I am guessing that BBmpeg does not use both CPU's in a dual system? Hmmm... if I set it to 3 "P" frames... that will make a total of only 9 frames per GOP. I wonder if that will hurt resolution because there will be more I frames?

Glenn