Minimum bit rate for standards compliant DVD?

[Jenny Davis]

I've done quite a bit of reading around to find the minimum allowed bit rate on a standards compliant DVD, but I'm now more confused than ever. I've read it can be anything down to zero or that it should be 2Mbit/s. Does anyone have a definitive answer?

[foxyshadis]

I'd be willing to bet that's an area where the specs are too vague to bother looking for an actual number, because each player would interpret it differently. The best option might be to make a disc with a feature where the bitrate dips lower and lower and see where that causes most players to fail (if ever).

[dragongodz]

I'd be willing to bet that's an area where the specs are too vague to bother looking for an actual number
well i have not come across anything on the net saying a minimum value was part of it. lookibng at experiences people have had though has shown that most dvd players are fine with no minimum set while a few pioneer and sony models(from memory) would stutter unless a minimum of something like 300kbps was set.

I've read it can be anything down to zero or that it should be 2Mbit/s.
i would like to know where someone would get 2mbps from, thats ridiculous. hmm didnt Tmpgenc limit the minimum to that in certain modes or something ? thats probably where that came from. i personally wouldnt be listening to someone saying you had to have a minimum that high unless they could back it up with some sort of proof as to why.

[jano22]

From memory too:

There are a ninimum recomendation about minimum bitrrate but actually has no sense. On firts dvd days, read units has no able to provide a low and hight tase of transfer. Dvd-video disk manufacturers was forced to respect this limits (theonly one i remenber is the upper limit of 9.8 MBit/s). Nowadays, dvd reader units are best and the minimum limit must be ridiculous. If a standalone has problems with very low bitrrates, is a firmware problem surely.

[Jenny Davis]

Hi guys, thanks for the replies.

It' a difficult one, that's for sure. Interestingly if I start a multipass VBR encode in CCE, which you know is a very well respected encoder, as its defaults it gives MIN:2000 AVG:6000 MAX:9000. So even CCE believes the 2Mbit/s theory. Also although I haven't seen it written in very many places, the 2mbit/s figure is the only figure that repeatedly gets mentioned as being the minimum for a standards compliant DVD. But you are right it seems much too big!

BTW Canopus procoder2 as default sets the min to 0, so who's right?

Jenny

[Boulder]

That's just some default settings for the profile, they need to set some kind of a default and let the end user modify it to his needs.

Even if you set the minimum to 0, you get something like 150-200kbps on completely black scenes. FYI, HC doesn't even have a minimum setting ;) I have a crappy old Pioneer DV-343 (something like 6 years old) which has not had a problem with a minimum of 0kbps.

[Jenny Davis]

That's just some default settings for the profile

Oh yes, I realise that, but it seems more than coincidence that they would choose a min of 2000 as a default value when that's also the only figure I've ever seen quoted as a requirement for a DVD standards compliant disc. After all, they could have chosen zero or 1000 etc.

[Boulder]

http://www.dvddemystified.com/dvdfaq.html doesn't say anywhere that there is a minimum bitrate one should respect so I don't think it exists. I'm quite sure it would be there if there was one.

[dragongodz]

but it seems more than coincidence that they would choose a min of 2000 as a default value when that's also the only figure I've ever seen quoted
where have you seen this quoted though and by who ?
also have you thought that maybe these people are quoting it as the minimum because they saw it as default in software and not that they actually know anything ?

to add to Boulders link i give you this aswell
http://www.mpeg.org/MPEG/DVD/Book_B/Video.html
again no minimum is specified where resolutions and maximum bitrate is. this should tell you something.

[Mug Funky]

there's tons of pressed discs out there that go all the way down (in pure black scenes of course) to as low as ~200 kbps.

how these play in _every_ player is a matter of debate, but in theory a clever enough player can simply stop reading while the buffer corrects itself.

that said, if you were to test this theory, go find yourself an old Pioneer player, as they have difficulty with a lot of things, one of which is low->high bitrate "transitions". i've only seen this with 1 rejigged stream, and that was on a transition between a still and a piece of handheld talking-head footage. that may be a rejig issue though... the player played the still part way too fast, then choked on the talking head, about 1 GOP in, freezing, stumbling, then freezing until the unit is turned off.

(perhaps i should point to this post in the rejig thread? that means finding something uploadable that reproduces it...).

[Jenny Davis]

Here are some places where the 2mbps minimum is quoted:

http://dvd-hq.info/Calculator.html - read the bitrate section
http://dvd-hq.info/forum/viewtopic.php?t=115&sid=a7b0132d2bcd54f5cc535b12c500c4e1 - read last post
http://www.doom9.org/index.html?/dv/guide.html - read the CCE and TMPGenc setting parts
http://forum.videohelp.com/viewtopic.php?t=222898 - look at the CCE part (or search for 2000)
http://forum.doom9.org/archive/index.php/t-87961.html - general thread mentions 2000
http://forum.doom9.org/archive/index.php/t-45711.html

Note, I am not proposing that these links provide proof that 2mbps should be the minimum bit rate for a standards compliant disc, it just gets a mention. There were a couple of what I thought were more authoratative posts, but I just can't find them now.

I think the real problem is not that there is a minimum bit rate in the DVD specs, but that in the real world if you want to make a disc that has maximum compatibility, which is what I want, there has to be a minimum figure for the bit rate. It's not desirable, it's just real world.

Jenny

[dragongodz]

read the bitrate section
to quote the relevant part
Some programs prefer files where the bitrate never drops below a certain value (ex., 2000 kb/s). If this is the case with your authoring program, and the value suggest by the calculator is lower, increase it to that value.
notice what i made bold ? this isnt saying a dvd player will have problems but maybe specific encoders or authoring programs. i would use something else if i came across these programs.

read last post
and again the relevant part
Some old players have problems when the bitrate approaches 0, so it's usually a good idea to keep the minimum at 2000 or so, if you want to make sure the disc plays everywhere.
again see the bold part ? there is a big difference between approching 0 and 2000. where he got that figure from i have no idea. i can only guess by looking at defaults that some encoders use because its not based on any evidence he gives nor even makes sense in the context of the first part.

i could keep going through the rest but you will notice there is not any evidence given or mentioned by those that say you should use 2000.

but that in the real world if you want to make a disc that has maximum compatibility, which is what I want, there has to be a minimum figure for the bit rate. It's not desirable, it's just real world.
as i already mentioned there are real world results. for example quite some time ago early in DVD-Rebuilders life there was some problems found with certain brands/models(namely sony and pioneer from memory) that didnt like a minimum bitrate below 300(again this is from memory). so jdobbs set the minimum to 500 and that cleared up the problem. he has even recently dropped that down to 300 aswell.

so if you are really that worried then indeed set your minimum bitrate up a bit, such as 500 or 600 or whatever. dont however believe that thats meant to be any sort of minimum of the standard though.
for a little real world example i just looked at a commercial dvd i have ripped to my hard drive for testing with DGmpgdec. it has sections where the bitrate falls well below 2000, for example the smallest i saw was 0.284Mbit/s. i am sure i could go through plenty more and find the same thing. that should tell you the figure of 2000 quoted is not real.

[Mug Funky]

additionally, the only times i've needed to set a minimum rate was for quality reasons rather than compatibility - some encoders (i'm thinking specifically of the mpx3000) have rather bad rate-control, and need a reasonably high minimum rate simply so that if they use the minimum rate on a scene that needs much more, it wont look terrible (ie giving 1mbps to a fast, grainy pan). we'd noticed there were less reports of blocking by our testers if the minimum rate was raised. this would make sense, because 2-pass encodes require the input to be the same on both passes, but if one uses a standards-converter it will be slightly different every time it's played out, so difficult parts might not be spotted.

that exception doesn't apply to most software encoders - they're intelligent enough to know where the bits should go.

[writersblock29]

@Jenny Davis

I do a lot of videography work professionally, and most of it winds up on DVD. Out of literally thousands of burns of hundreds of projects to hundreds of clients (and hundreds of different set-top players), I have yet to have any complaints while using a minimum bitrate of 0, maximum 9K, within CCE SP 2.5. Of any playback issues I've faced, all were due to either bad burns (the replacement disk would function beautifully), cheap media, or a combination of both. Now that I stick to higher-class media, I haven't had to replace a faulty disk in nearly a year now. That aside, the encoding perameters -- using 0 as a minimum -- never seemed to introduce any issues. Not that this "proves" anything as far as DVD specs go... it's a tale of experience, I guess... but still, I'm confident in recommending a 0 minimum while encoding. If anything would cause stuttering, I'd think keeping your maximum too high would do it, since your audio bitrate adds to the total sum in the end once your disk is authored and burned; if your video bitrate spiked at the same time as your audio bitrate, I'd think it would cause trouble if it exceeded the maximum allowed.

That's my two cents... and I beleive I owe you change!