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Bitrate Setting guidance

 
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uruk-hai



Joined: 06 Jan 2004
Posts: 4

PostPosted: Tue 6 Jan 2004, 10:57    Post subject: Bitrate Setting guidance Reply with quote

Sorry I know this question had been asked thousands times. I have done many homework but still could not find the exact answer I want.

I usually use TMPGEnc Plus to convert AVI (Xvid, DivX & MPEG4) moive clips into MPEG2. I know that the higher the bitrate the better. But I believe that should be an optimal point beyond which higher rate would only give marginal improvement. Of course I want to fit as many file in the same DVD disc.

I come across DivX 5 encoded file whose original bitrate is less than 800K.
There are also XviD encoded file whose bitrate is over 2M. Is there a ratio that I can apply when setting the bitrate in TMPGEnc for different encoding codecs, original bitrates and half and full DVD resolution?

Garbage in garbage out. I think setting 8000K bitrates for a 800K DivX5 is a waste, isn't it.

Any help is mostly welcomed.
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RMN
Site Admin


Joined: 04 Feb 2003
Posts: 587
Location: Lisboa, Portugal

PostPosted: Thu 8 Jan 2004, 20:02    Post subject: Reply with quote

DivX uses more advanced compression than DVD (which is an older standard). Given the same bitrate, DivX will usually produce much better results than DVD. So the rule is, use the highest bitrate you can. If you want to fit a 90-minute movie into a DVD, you can use a bitrate of about 5100 Kb/s (if you use compressed sound, you can use more than that), so there's no reason to use a lower value. The empty space on the DVD would simply be wasted.

BTW, converting DivX to DVD is a waste of time and money. Get a graphics card with TV-out and connect your PC to your TV. You'll end up with better quality and no conversion necessary (and you'll also be able to play games, Flash movies, Quicktime, etc., on the TV).

RMN
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uruk-hai



Joined: 06 Jan 2004
Posts: 4

PostPosted: Fri 9 Jan 2004, 10:26    Post subject: Reply with quote

rmn wrote:
So the rule is, use the highest bitrate you can. ..., so there's no reason to use a lower value. The empty space on the DVD would simply be wasted.

I agree with the statement provided you have good quality source e.g. AVI that is ripped version of DVD-9.

I work with AVIs that are heavily compressed (e.g. 800MB for 1.5 hr moive) to reduce its size for easy circulation in the internet and sources that were dubbed from low quality VHS or hand-held DV camcorder.
In these cases, if 4500 Kbps and 8000 Kbps make little difference, then I can fit more movie into the same disc.
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core



Joined: 30 Dec 2004
Posts: 3
Location: Des Moines, Iowa

PostPosted: Thu 30 Dec 2004, 4:00    Post subject: Reply with quote

Ok, say if one accepted the fact that converting divx to DVD was a waste of time but really really wanted to do it anyway, is there some quick-and-dirty formula for the necessary bitrate increase which would yield acceptable quality? Say add 20% to the divx bitrate or something?

After all, you don't want lug your whole PC and nifty TV-out card to your buddy's place just to show him the latest underground documentary.

I do find even VCD quality *gasp* acceptable for this kind of thing, but if I can spend a few more bits and preserve more of the original quality I'll do so. I just don't want to go overboard and split my 6 hour senate hearing out over 3 DVDs if it won't add anything. Sounds like I have a lot of trial and error in store for me. I just don't have the eye for this kind of thing... I still think VHS looks good! LOL
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RMN
Site Admin


Joined: 04 Feb 2003
Posts: 587
Location: Lisboa, Portugal

PostPosted: Thu 30 Dec 2004, 5:06    Post subject: Reply with quote

Different compression methods (ex., MPEG-2 vs. MPEG-4 / DivX) deal with different types of data in different ways. In other words, some types of footage would need a much higher bitrate, while others might look fine even at the same bitrate; there is no "magic formula" to decide how much is necessary to get "good quality" (which is a subjective concept, anyway).

Generally, use the highest bitrate you can (as long as it still fits on the disc). If you are trying to put as much as possible in a single disc, make a few tests with progressively lower bitrates and decide what kind of quality you find acceptable.

RMN
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