25p DVD okay for pal?

musman wrote on 2/8/2006, 12:12 AM
I know I've asked some questions about this in the past, but I wanted to make sure about this before I made this DVD and sent it out to pal land festivals. I've found that Vegas 6 does an excellent job making 25p MPEG2 files from 24p footage. Looks much better than the 50i or interlaced version Vegas 6 makes from the same material. Since I shot on film and have been editing from a 24p timeline, I'm reluctant to add the interlacing unless it is completely necessary. I could have sworn I read somewhere (but can't find it now) that 25p was fine for pal tvs. Is this really the case? Also, just to double check, I don't need to do anything to the audio, do I?
I know another option is just to make a 24p DVD, but I'm still reluctant to do that because of the sped up audio issue. I know that 24p audio will get sped up 4% b/c the audio will have to run at 25p now. But, shouldn't the speed difference actually be 4.096% as 25p- 23.976p= 1.024 & 1.024 x 4 = 4.096? Anyway, my unproven workaround for this is to add a pitch shift in SF to transposition ratio .96 (actually I could only get it to .95998), selecting a mode like music or speech, selecting preserve duration, then rendering out. My 'test' to simulate what the pal speed up will do is to take the new file and again in SF apply a Pitch Shift with a transposition ratio of 1.04 w/ preserve duration unselected. Seems to fine to me, but if I really trusted it I wouldn't be trying to make 25p DVDs to avoid the whole issue.
Thanks ahead of time for any help!

Comments

farss wrote on 2/8/2006, 2:54 AM
As far as I know the only options you have are to make a 24p DVD or a 50i DVD for PAL land. The 24p DVD will get played back by the player 4% faster as you've noted however I believe this is pretty common and the pitch shift we live with all the time and no one notices. However the 24p standard is only 720x480 which is rather lower res than the 50i DVD standard of 720x576 and that I think is noticeable.
However if your source material is true progressive I'm at a loss to see how you'd gain anything between it ending up as 25p or 25PsF. In other words the display device still needs to display the same frame as two fields otherwise the flicker is just unbearable, pretty much the equivalent of the two blade shutter in 35mm projectors.
As your source material is film and hence 24p there's really no way to make it anything else, that'd imply being able to increase temporal resolution which is impossible, it's only possible to reduce temporal resolution.
So when you convert to 50i there should be no interlacing artifacts as the two fields originated at the same point in time, this is even simpler than 24p or 24pA, there's not even the complication of pulldown involved, the 50i (technically it's 25PsF) should look exactly the same as 25p if you could create such a DVD.
I've made many such DVDs, all made from 1000s of still images so there's no way they're anything other than 25PsF, but they're encoded to mpeg-2 as 16:9 50i and they look glorious.
Hope this helps.
Bob.
PDB wrote on 2/8/2006, 12:51 PM
this might help...

http://www.sonymediasoftware.com/forums/ShowMessage.asp?ForumID=4&MessageID=319532

Sorry, just wanted to add that I have in practice edited a 25p DVD on DVD Architect and it played back fine on a Pal dvd player onto a regular Pal tv set...

hope that helps...
farss wrote on 2/8/2006, 1:58 PM
A kind of frustrating thread that one, Sony asks a question, gets an answer and we never hear back from them!

There is a difference in editing 25p natively as compared to editing it as 50i, temporal effects are rendered differently.

Question is, did you tell the encoder to encode as progressive at 25fps and did DVDA accept the stream as compliant?
As I said in that past thread visually I don't believe there'll be a difference, the encoder always encodes as frames, even if the source is 50i. The encoder should be able to do a more efficient job with 25p source compared to 50i source but ultimately it has to end up as 50i for the TVs to cope.

Bob.
musman wrote on 2/9/2006, 11:16 PM
Just wanted to say thank you all for the posts. Still seems a little tricky no matter what you you do unless you do the interlaced 50i method, but that really looked crappy in comparison to 25p in my tests on my lcd.
Anyway, there also seems to be a bit of the do you trust Vegas more or the DVD going on as well. I think I'd still trust Vegas to stretch my pixils better than a pal DVD player, so I guess I'm still going to go the 25p route rather than the 24p route.
Thanks again for all the input!
farss wrote on 2/10/2006, 12:16 AM
How are you previewing this?
Something wierd I just noticed.
I created both a 25p and a 50i clip from a still.
Put both into a 50i project and the 25p clip looks way better however if I change the Project Properties DeInterlace method to None they look exactly the same?
Bob.
musman wrote on 2/10/2006, 9:55 AM
Really? That's weird. I'll have to check that out. Not sure what that means and I'm getting a little lost honestly. I'm just previewing on a Dell 2405.
farss wrote on 2/10/2006, 12:12 PM
I don't have an explaination, I'm back capturing at the moment but I should dig deeper into the manual.

See when a camera captures in interlace line averaging is used to reduce line twitter and average out noise. That's why on the DVX100 in P noise goes up and vertical res goes up compared to shooting in interlaced.
However when Vegas goes from P to I it doesn't do that as far as I know, that's why there's so much drama over line twitter etc when handling high res stills.

Now if you shoot 24pA on the DVX100 it's a 60i stream but by removing pulldown you can retrieve the original 24fps image sequence, not a pixel changed.

Starting from 25p material and rendering as 50i one should be able to simply merge the two fields back to frames and get the exact same 25p material back. That's why I was saying encoding as 50i shouldn't matter, it should look exactly the same.

A 24p DVD is still played out to the TV as 60i, a 25p DVD is still going to get played out as 50i. The advantage to authoring a 24p DVD over a 60i DVD of the same material is the 24p stream doesn't contain redundant fields so the encoding is more compact, i.e. bandwidth is conserved. I think in fact it's a fairly dramatic improvement too as the encoder will convert the 60 fields into 30 frames and encode that however some of those frames contain a field from one frame and a field from the next frame so there's a lot of difference between that frame and the prior one.
The same doesn't apply to 25p / 50i as there's no redundant fields and the mpeg-2 encoder merges fields to frames prior to encoding.

Bob.