Filesize at half d1 vs. full d1

[haloblack]

After putting it off for many months, I decided to start consolidating some svcd's that I've made to dvd just to save space. I wanted to maximize time-per-disc, so I ripped the mpg from the svcd and then reencoded to half-d1 in tmpgenc. My original file (the rip from the svcd) is 813Mb, and the video-stream-only reencode is 705Mb! The Tmpgenc project wizard (which I didn't use for the final product) says that half-d1 with mp2 audio can be used to put 495 minutes onto a dvd, but I don't see that happening with just over 100 megs of space saved by reencoding to half-d1 - and that's an elementary stream that doesn't include audio! I'm sure that I'm missing something obvious here, but I'm stumped. Shouldn't going from d1 to half-d1 save me a *lot* more space than this?

[johns0]

Going from dvd to 1/2 dvd doesnt automatically save you space,its the bitrate that you can use with 1/2 dvd that drops the file size so a bitrate of around 3000kbps looks better on 1/2 dvd than on dvd,498mins to fit on a dvd is just a rough estimate that pertains more to vcd standards,its the file size that counts in making a dvd which is produced by what bitrate you use.I save more space by using a bitrate of 3000kbps and using tmpgenc cq encode at 80.

[haloblack]

its the bitrate that you can use with 1/2 dvd that drops the files so a bitrate of around 3000kbps looks better on 1/2 dvd than on dvd

So if I read you right, using full-d1 encoding settings and dropping the resolution to half-d1 isn't enough?

(a momentary pause whilst I do a forum search. I'm always yelling at people for not doing research, I guess I should dig a little myself... )

Hmm... I encoded at average 2k/max 8k/min 0, and I'm seeing suggestions of max 3.5k max/1k min. I think I need to try that out and compare. I really wish I could understand the whole resolution / length / bitrate correlation to filesize. It takes me forever to grasp any math that's harder than x+y=z.

Grr...

[wulf109]

Whether you encode at 1/2D1 or D1 the resolution does not effect file size.
The average bitrate you use dtermines files size,not resolution. D1 is 720x480 and 1/1D1 is 352x480. In theory using 1/2D1 allows you to use a lower average bitrate because there are many less pixels to encode. The fewer the pixels the more bits per pixel. But bitrate as it gets lower has more to do with artifacts then resolution. Since your converting SVCD(480x480) going to D1 may not look visibly better,only your eyes can answer that question.

[haloblack]

I'm seeing suggestions of max 3.5k max/1k min. I think I need to try that out and compare.

I ran the encode with those settings overnight, and the file size went *up*! This is maddening...

[bugster]

Liste to what everyone is saying. It is the bitrate and playing time that affect filesize. However, if using some form of variable bitrate encoding (which it appears you are) then it is the AVERAGE bitrate that is improtant in terms of filesize. Max and min values only affect quality and bitrate distribution.

Using TmpGenc, the only way to use VBR and ensure a specific Average bitrate (and hence filesize) is to use 2-pass VBR. where you can set MAX, MIN and AVERAGE values for the encoder to use. If you use CQ mode or any of the other VBR methods offered by tmpgenc you cannot guarantee the final filesize as you cannot specify the Average bitrate.

Hope this helps.