File size of final DVD- need manual bitrate setting..

[Ramas]

Hi guys, I have converted 1 h 57 min DivX 16:9 movie into DVD. Final size was 3.21 GB with auto avg bitrate 4599,3 kb/s. I now that DVD-R or DVD+R supports 4.3 GB or more with double layer. Question- Can you put to the program some button for force manual bitrate setting?

[JJ]

You want to increase bitrate from original DivX-files rate? Why? Quality is NOT increased, just space wasted.

[JJ]

Adding to previous; Manual setting would be a nice option, just converted 21minutes episode and DivXtoDVD set it to 9000 average when original had only 998. Sometimes you can drop bitrate a bit without losing anything visible. That just might be enough to fit whole movie or more episodes to same DVD.

[bigly]

@JJ: Ramas was correct, the bit-rate of the DivX has nothing to do with it! To convert to MPEG-2, any application has to sample what comes out of a codec, not what goes in. Therefore, to get as close to a 1:1 representation of the output of a DivX/XviD in MPEG-2 format, the higher the bit-rate the better. It is widely accepted that anything below an MPEG-2 bit rate of 3000kbits/sec introduces significant quality reduction compared to the source (i.e. the DECODED XviD/DivX etc.) @VSO: Almost same question as Ramas! Based on that, how is it that DivXToDVD encodes a 1hr45min XviD into only 2.1Gig of MPEG-2 data? 1hr45min of content on an actual DVD (i.e. good quality MPEG-2) would normally fill >4Gig. Is it because: 1. DivXToDVD is letter-boxing and only encoding the actual picture part of a frame. (Is that a 'feature' of MPEG-2 to allow un-encoded bordering space?) 2. DivXToDVD forces a low MPEG-2 bit-rate. (Quality seems too good for this!). 3. Something else....please explain!.... I am worried that for some reason DivXToDVD isn't creating as close to a 1:1 of the source as possible!

[JJ]

bigly: I really don't understand you now. I said that increasing bitrate from ORIGINAL bitrate is NOT improving quality. For example; if you have a movie with bitrate of 6000, increasing it to 9000 and keeping same pixel-size of picture is NOT improving finished quality. Just like with MP3 - if you pack it once with 96kbits and then repack with 256, you just increase filesize without ANY improvement on sound. DVD supports smaller picturesize, 352*288PAL / 352*240 NTSC, with most TV-shows that quality is more than enough. You can fit almost 500minutes of video to DVD-R disk with that format, and it will still look as good as in TV. Not movie quality, but usually originals are captured from TV and their resolution IS low. Forcing them to hi-standard uses just more space without any better picture.

[bigly]

Sorry about the bit-rate - thought you were implying a DivX @ 1000kbits/s should be MPEG-2'd @ 1000kbits/s which is blatently wrong! (Obviously we aren't allowed to discuss the fact that the majority of DivX some people have, they don't know the bit-rate on the original DVD!!! ) OK, OK.... I've registered to chat to ya!!!! So you are saying the reason that DivXToDVD comes out with file sizes that are more than 50% smaller than WindDVD, DVDSanta, D.I.K.O. ...(the list goes on)...is that it deliberately encodes only 50% of what is available? (Using this lower-quality, 'long-play' ability of a DVD?) So are we affectively getting a transcoded version of the output of our DivX/XviD Trust me, I did a 6hour test on a 20min XviD yesterday using 5 different apps. Allowing the apps to control the bit-rate based on high-quality settings (some just did it, without such options as does DivXToDVD) showed that DivXToDVD encodes were at least half the size of all of them. I'm not saying the quality is bad - in fact it is bl00dy amazing - it kicked butt on WinAVI (which was x2.5 encoded file-size on DivXToDVD) - I just NEED to understand what a 'tool' is doing when compared to 5 well known commercial methods it seems to be doing it in half the file size - for trustability factors sake!

[JJ]

Well.. I did NOT say that DivXtoDVD is using smaller size. I suggested that there would be an option to use it. And I'm talking about screensize. Obviously when screensize is 1/4th of big one, bitrate can be MUCH smaller too. If you make calculations - 352*288 24bits totals 2376Kbytes/frame, while 720*576 24bit totals 9720Kbytes/frame. I don't have a clue about HOW DivXtoDVD is managing those small (file) sizes with great picture. I would guess that it reduces amount of color, like using 16bit color instead of 24bit. That would reduce a lot, 720*576 16bit totals to 6480Kbytes. But as I said - I don't have a clue

[bigly]

Sorry for mis-quotin'! The resolution thing makes sense. I didn't know a standard DVD player could alter from the 720xblah resolution. I wonder why the other apps who 'specialise' in this don't use this optimation in resolution matching to a lower res DVD standard? Anyway, I'll see if I can check the theory with a conversion that has a high source resolution - see if it starts to use the 720xblah resolutions again meaning it would deliver similar file sizes as the other apps. It's exactly the how I'm trying to work out. I love the thing but I want to know that my limited viewing on limited equipment isn't hiding any questionable quality cuts! (Like colour compression!) (I.E. If I take a DVD to a m8 with 48" plasma TV, will it look really bad in comparison to some other DVD encoding apps?)

[JJ]

Very few will ever notice if 16bit color is used. Only places where it can be seen is close-up of human face; starts to show lines when there is not enough colors to spread. Or some big walls that have bright light and shadow; same result. I have noticed this a bit on converted divx; but it usually has been there already on DivX, result of bad packing. Well .. we will see what happens with this software, looks promising so far!

[JJ]

I checked a lot of files I have converted; their bitrates are fluctuating a lot. Seems that DivXtoDVD is achieving smaller file sizes by simply NOT padding bitrate up if it drops really low. This results in smaller filesize as only needed bits are encoded, not padding up unneeded "empty" bits. However - this can lead to problems on some players, as they are not able to produce good picture with really low bitrates. There is NO limit on DVD-standards about how low bitrates can be, they can be as low as 0 if needed. IF some player is not supporting that, then that player is not up to DVD-standards. More on that: http://dvd-hq.info/Compression.html

[bigly]

Nice work! Problem is I've been telling people it's recording in Half-D1 format! I'm sure a VSO person confirmed what you said about it using lower resolutions! (Maybe on the 'other' listed English VSO forum.) JJ, can you confirm that you did see it set the "Output Resolution" to Half-D1 (352*288) because since I installed the latest version ALL of my encodes report Full-D1/DVD resolution IN THE LOG (which I assume we must trust). Your minimum bit-rate theory seems excellent but why would other encode developers not use this 'trick' if it were that simple to get file-size down? (As this probably helps towards the high encode-rate too!)

[JJ]

[bigly]

OK - I fully understand what you are saying and think you are probably onto something with player problems @ low bit-rates BUT can that really be the only reason the file size is so low with DivXToDVD in comparison to similar encoders/apps? Actually, don't answer that...I feel an experiment coming on.... I will try to encode an identical file with MainConcepts MPEG Encoder (as I have a demo installed) with bit-rates set@: minimum=0 max=8000 average=whatever DivXToDVD calcualted initially IN THE LOG for the same file (e.g. not the actual average after encode). This should prove whether it is the main factor in the reduced output size or just a factor in it as the resulting files sizes should be very similar. JJ, stop me if you have already done this comparison with another encoder!

[JJ]

[bigly]

OK this was a dissapointing experiment! The ONLY way(s) I could get the (configurable) MainCondept encoder to come up with the same (low) file sizes as DivXToDVD was: 1. Set the average bit-rate to the actual average which DivXToDVD finished with. Well duh! This is obvious and proves nothing other than than MainConcepts rate control was doing as I told it to! BTW, as expected, the quality with these similar file-sizes was nowhere close to that of DivXToDVD so it isn't as simple as using a low average bit-rate (, as we knew already). 2. I forced the VBR rate-control to deal with a constant Quantisation (quality) factor. This could have been a possibility for DivXToDVD's low file sizes except for, as expected, with a constant Q factor to match DivXToDVD file sizes, output quality was again terrible in comparison to DivXToDVD. When I attempted to replicate what JJ suggested DivXToDVD may be doing by using it's calculated average bit-rate and no padding to a minimum bit-rate, the MainConcept encoder seemed to be configured to faithfully keep close to the average bit-rate regardless of not having this minimum bit-rate set. In other words, there is simply no way for me to configure it to, "use the average bit-rate as an initial quality guide but use the lowest bit-rate possible to maintain that quality" which is what DivXToDVD may be doing. [I have learnt and played with a lot of the advanced settings in attempt to replicate this behaviour to no avail.] When I get time I will see if TMPEGEnc has the settings to configure this behaviour and re-try the experiment. ______________________________ During reading up on this it occurred to me that 'playing' with GOP structures could help manipulate bit-rate whilst still retaining quality, for example, if more than 'normal'(?) B frames were used. Does anyone know if that could be the case? E.G. Does DVD spec have a specific fixed GOP structure?

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