Understanding a bitrate

[Nelson37]

DVD has to be either 23.976 or 29.976 FPS, AVI's are often anywhere from 12 to 30 FPS, or even higher.

DVD has to be 352x240, 352x480, or 720x480, or the PAL equivalent, AVI's can be a hundred or more different incompatible resolutions.

DVD are usually MPEG2, occassionally MPEG1. There are 3 or 4 different versions of DivX, one or two Xvid's, and probably several more I haven't heard of. Each of these have different rates of compression efficiency.

DVD are usually made by enthusiasts who give a damn about quality. AVI are often made by kids who must be viewing them on 3" screens, though there are some of good quality.

It is simply not possible to come up with a generalized rule to take into account the variability of the source. It is trial and error.

[duhmez]

If the avi was made really well, and looks great, and is high res, you may need it to be 3 times larger (or more) to look the same as far as you can tell.

You will also have to perhaps add black borders to it (letterbox) to make it look right, and or resize the video. If it is 4:3, it's a much easier conversion.

Now, if the avi is done like crap and looks bad already, it probably does not have enough bitrate to it or has a lousy source,a nd will still probably need to be 2>3 times bigger to look just as good, in your eyes.

If the divx looks really _really_ good (they CAN btw, not all divx are made by n0obs ) then you can get away with not so much extra bitrate, maybe it will look a little less good, but may still look GREAT on an interlaced television........

Lotta factors to consider.

here is one specific example: I have a fantastic quality divx file, 512x384 1225 kilobits per sec.

I resized it to 352x480 (So it would be dvd compliant, 4:3) and set the bitrate average to 2000 kbps. (min 500 max 9000 average 2000)

The final product, my eyes can't tell the difference (almost can't tell, it is _slightly_ not as good. On the interlacedtv screen though , it looks perfect)

This will not be true for all avi files, it's just one example. If I encoded as mpeg 2 352,480 1225 kbps, it would look like total crap and be FULL of blocks and be useless.

If I did somehting really strange, and reencoded right to divx again @ 1225 kbps, it would then look WORSE. So there are 2 factors involved. When you decompress and reocmpress to any lossy format, you lose some quality automatically. Its twofold going from divx to mpeg 2, because mpeg 2 takes more bits to achieve same end result as divx.

[alex1234]

Work it out based on your required output size.

There is no required output size - I will go for any size that does not loose quality. But I don't want to over-size, this is the goal and this is why I asked my question

It is simply not possible to come up with a generalized rule to take into account the variability of the source. It is trial and error.

Unfortunatelly I can not try - my DVD player does not play re-writable DVDs, every time I try, I loose a disk. I have a laaarge screen TV that makes visible the quality very well, not as PC monitor where all DVDs look good

DVD has to be 352x240, 352x480, or 720x480, or the PAL equivalent, AVI's can be a hundred or more different incompatible resolutions

I think resolution has to be handled this way (for NTSC DVDs):
1. if source resolution <= 352x480 convert to 352x480 DVD
2. if source resolution > 352x480 convert to 720x480 DVD
Correct me if I'm wrong, but there is no point of converting < 352x480 source to 720x480 DVD

If the avi was made really well...you may need it to be 3 times larger
...if the avi is done like crap...and will still probably need to be 2>3 times bigger to look just as good...

These are the numbers I'm looking for!

Here it is:


General recommendations

1. For a VERY high quality AVIs produce 3 times larger MPG
2. For a moderate quality AVIs produce 2-2.5 times larger MPG
3. For a crap quality AVIs experiment, or use 1.5-2 times larger MPG

These regommendations will garantee no qality loss. If you want to save more disk space - experiment.

How does this sound?

[Gazorgan]

The 2.5 Ratio would be true for 'perfect video'. But it doesn't work for a 700 MB 2 hour AVI.

Things like letterboxing and 23.97/29.97 fps affect the final product.

I could create a formula for you, but you would need to know the following factors:

Objective
Length of Video
Resolution of Video
Audio Bitrate
Audio stream type
Interlaced or Progressive
FPS

Subjective
Quality of Video
Quality of Audio
Desired final product quality
Minimal required resolution (D1, 1/2D1, SVCD, other)


The end results will mostly be "Don't bother" or "VCD". Sorry, but 600 MB AVI's just suck compared to the original DVD. 600 MB AVI's make good VCD's, but poor hi-res DVD's. Short ones make good CVD/SVCD's.

MPEG isn't some magical codec. It's roughly 2-3x better than MPEG2, only if you let it be!!! It like ASF's from the 1999's, people would make these 200 MB videos because everyone was on dial-up, not because it was a good size to watch(they sucked).

[alex1234]

Gazorgan,

it looks like I'm a bit misunderstood here - my goal is not to produce MPG (target) with a better quality than AVI (source) but to produce the same quality MPG with the minimal disk space. No matter what quality is the AVI, I want to get the same quality MPG with the minimal disk space.

To get the same quality MPG I could selectect 4000 bitrate - no doubt the resulting MPG would have the same quality as the source AVI. But it would be 8 times larger than the AVI!

Back to my example: 600MB moderate quality 1.5 hours AVI. According to my formula I would convert it to a 1.5GB MPG (2.5 ratio) and I state (based on our discussion in this topic) that it would have the same quality as the AVI (please note, the AVI, not the DVD this AVI was created from!!).

[ZippyP.]

Back to my example: 600MB moderate quality 1.5 hours AVI. According to my formula I would convert it to a 1.5GB MPG (2.5 ratio) and I state (based on our discussion in this topic) that it would have the same quality as the AVI

By my calculations (using the DVDRhelp bitrate calculator) the bitrate of the mpeg would be 2,000 Kb/s. This would be good for 1/2 D1 352x480 or SVCD 480x480, and even better if you used 2,000 as the average bitrate in a 2-pass VBR encode of the above resolutions. It would be too low, however, if you tried for full DVD resolution.

[alex1234]

ZippyP,

I do not see how this bitrate calculator (and therefore your calculations if they were based on this calculator) can be of any use at all.

Look, I enter a 60 min movie and it suggests me to use 9570 bitrate. It does this because it will fit into 4.7 GB range and my resulting MPG will be 4.7 GB. Great! Now, I bet you that if I encoded this video with 3500 bitrate the quality of the video would be exactly the same but I would fit my movie into a 2.2 GB file. Which file do you like more, 4.7GB or 2.2 GB?

[ZippyP.]

ZippyP,

I do not see how this bitrate calculator (and therefore your calculations if they were based on this calculator) can be of any use at all.

I used SVCD setting, 2 x 74 min CD's (total 1.48 GB), 90 min. video length gave 2,000 avg. bitrate.

[duhmez]

This is the deal. If you want to put this one movie on a dvdr, and you do not want any other content on the dvd, and it is 1 hour,

Then resize to whichever res is closest 704,480, 720,480, or 352,480,

Then encoode using CBR @ 9400 KBPS.
Also of note: If it is widescreen, you must use 704(720x480) as 16:9 is only supported on full D1! (Or add black borders....

[videocheez]

I have made about 150 DVD's from AVI conversions since I started learning about this stuff earlier this year and gave up on trying to save DVD space because I want quality. Especially if I want to show of my final productions to friends and family. I have found that if I have a 1.5 hour ymovie and I use the maximum bitrate allowed to fill-up a DVD that the quality is just about as good as the source AVI.
If my source is around two hours long and contains a lot of night and action scenes, the resulting DVD is acceptable but the quality is not as nice as the original 640x272 avi.
The folks here have given a lot of suggestions. I know blank DVD's are expensive but have you considered experimenting and trying out a few different bitrates?
After experimenting yourself, you can make your own rules to go by during future conversions.
BTW, I made about 40 coasters experienting but now I know what the end product will look like and the only time I get coasters is when I trying playing a first person shooter during a burn and I consume the burners cached memory and the write fails.

Good luck,

VC