N-Vop's Cause Audio Synch Problems on Philips 642?

[LisaB]

I am thinking that the combination of NVOP's on an avi that DOES NOT use packed bitstream leads to audio synch problems on the Philips.

I had a problemmatic avi which would play fine on the computer, but would go noticeably out of synch on the Philips.

Now, I always thought that N-VOP's were associated with packed bitstream, but this avi WAS NOT packed bitstream, but still had N-VOP's.....that is the only thing I can say could cause the problem.

I re-encoded the VBR audio to CBR, but this still did not help.

However, by re-encoding the video, the problem was fixed.....and my re-encoded video, of course, was packed bitstream but no NVOP's.

[FulciLives]

Hello

I just recently purchased the Philips DVP-642 and I must say that I am very impressed by the quality of Xvid video when viewed on a TV with this machine. A shame that it does shit PAL to NTSC but I still have my Cyberhome CH-DVD 500 for that

Anyways I just ran across this "guide" you wrote (is it here on this website if not it should be) called, "Lisa B.'s Guide to Standalone DVD Player Compatibility". I found it by accident doing some searching. This is the link I found it at ---> CLICK HERE

Anyways the thing about N-VOP frames is botherig me LOL

So far I've used AutoGK on 5 DVD movies. All have been 16x9 WS progressive FILM material. I selected the ESS SAFE option and the BITRATE SPIKE option to ensure proper playback on the Philips DVP-642. I'm doing Xvid with original AC-3 audio and use the custom size for 1400MB size. Also use fixed width of 640 pixels.

Here is the problem ... only 2 of the 5 came out with "0" N-VOP frames where as the other 3 came out with either 1 or 2 N-VOP frames each.

So I need to know more about this N-VOP thing and how to avoid it when encoding.

Sure enough the 3 with N-VOP frames need the rewind (though only for a moment) then back to play "trick" for the audio sync to come "back" to normal.

What are N-VOP frames? Do they effect Xvid (which is what I've been doing) or also DivX 6.x

How do you avoid them etc. ???

- John "FulciLives" Coleman

P.S.
I also noticed that AutoGK seems to mux or interleave the AVI with settings that do not "jive" with your guide/article.

[celtic_druid]

N-VOP's are used for duplicate frames. Only one frame is encoded and when the decoder encounters the N-VOP it simply redisplays the same frame. Any compliant decoder should handle them fine.

Were you encoding with bframes? Because as far as I can recall that if b frames are disabled and XviD encounters a duplicate frame then it will remove it and use an N-VOP even though the framedrop threshold is set to 0.

I am sure that you would have found the picture quality of an MTK based player impressive to and without most of the compatibility issues.

[FulciLives]

N-VOP's are used for duplicate frames. Only one frame is encoded and when the decoder encounters the N-VOP it simply redisplays the same frame. Any compliant decoder should handle them fine.

Were you encoding with bframes? Because as far as I can recall that if b frames are disabled and XviD encounters a duplicate frame then it will remove it and use an N-VOP even though the framedrop threshold is set to 0.

I am sure that you would have found the picture quality of an MTK based player impressive to and without most of the compatibility issues.

I was going to get the Pioneer DV-588A (MediaTek chipset) but the region free version is like $179 + shipping and I was at WALMART and couldn't resist the $58 price of the Philips DVP-642

However the PAL to NTSC really blows on the Philips DVP-642 so I wouldn't be surprised if I end up with the Pioneer anyways at some point although for now my Cyberhome CH-DVD 500 is still working (been years now) and does really nice PAL to NTSC.

I just encoded one of the movies that had N-VOP frames with Xvid using Divx 6 and the Divx 6 version did NOT have any N-VOP frames.

As I said I'm using AutoGK which is so nice and easy LOL but in the past (been a long while now) I have used the full blown Gordian Knot so maybe I will try that again with Xvid and be sure NOT to use B-frames.

The problem here is that AutoGK does not, as far as I can see, give an option for turning Xvid B-frames on or off. As I recall you have full codec control with the full blown Gordian Knot.

Only thing I like about AutoGK is that it has the "safe" ESS mode but what good is that mode if it apparently uses Xvid B-frames ... which it must ... since it sometimes ends up with N-VOP frames ... assuming of course what you said is correct i.e., that using Xvid B-frames can produce N-VOP frames.

At least if I use the full blown Gordian Knot I can be sure not to use B-frames but AutoGK also has "bitrate spike control" that I think Gordian Knot lacks.

This could all be solved, again assuming what you said is correct, if AutoGK would just not use B-frames when using the ESS SAFE option.

I guess I could get the same results with Gordian Knot as AutoGK but at least with Gordian Knot I can control the codec better so as not to use B-frames but again I worry about the "bitrate spike control". I wish I knew how to mimic that with Gordian Knot.

Anyone know how? ... or is there a way to not use B-frames with autoGK?

- John "FulciLives" Coleman

[celtic_druid]

I said without bframes.
Example, I just encoded a static test pattern clip.
bframes, no packed bitstream = 0% N-VOP's.
no bframes = 30% N-VOP's
bfames, no packed bitsream = 0%
no bframes + 100 for frame drop ratio = 99%. Only one frame was encoded since all frames are identical. The file still playsback fine and is smaller than the others.

Now if you were encoding with bframes, then I am not sure. Because if XviD did still drop dupe frames then it should have in my test since all frames were identical.

[FulciLives]

I see now.

I got confused.

I thought you had meant that you would get no N-VOP frames if you encode WITHOUT using B-Frames when in fact you meant the opposite.

Not your fault. My fault for the way I read it.

Last night I tried using the full blown version of GORDIAN KNOT to do a DVD to Xvid and I made sure to NOT use B-Frames and sure enough MPEG4 MODIFIER says this file has 57 N-VOP frames (0.03%)

So OK I understand now. You have to use B-frames so that you do NOT get the dreaded N-VOP frames.

But I'm confused because when I did the same DVD to Xvid using autoGK it came out with 1 N-VOP frame and the darn AVI starts out with out-of-sync audio (on the Philips DVP-642) until I do the reverse back to play trick. Of course if I only have to do that once in the whole movie I guess that ain't the end-of-the-world but still ... I'd like to not have any N-VOP frames.

To make things "more complicated" I did the same DVD using AutoGK but this time using DivX 6 and I used all the same settings in AutoGK as when I did the Xvid conversion and yet MPEG4 MODIFIER says that the DivX version has "0" N-VOP frames.

However the Xvid version looks slightly better than the Divx version. It is a slight difference but still noticeable ... at least on my computer monitor. Perhaps not noticeable on a standard SDTV but I haven't burned the Divx yet for playback on the Philips DVP-642

I find it annoying that of the 5 DVD movies I have backed up with AutoGK (using Xvid) only 2 of the 5 came out with "0" N-VOP frames.

- John "FulciLives" Coleman

[celtic_druid]

I wouldn't view N-VOP's as bad. Like I say they are only there when there are duplicate frames detected and they help compression.

I couldn't get XviD to insert N-VOP's with a ratio of 0 unless I disabled bframes though. By the same token I don't think that there is any way to stop it inserting N-VOP's if bfames are disabled since it is always going to find a black frame or two to drop.

[FulciLives]

Well according to LisaB ... N-VOP frames cause audio sync errors on the Philips DVP-642 and although I've had mine for less than a week ... so far ... she seems to be right.

Any Xvid I have played with N-VOP frames goes out of sync. This can be corrected by rewinding (only seems to need a moment of that) then hitting play again.

But that is rather annoying!

Blah

- John "FulciLives" Coleman

[celtic_druid]

Yeah, so you conclude that N-VOP's are bad.
My conclusion however would be that the DVP-642 is bad.

That said N-VOP's are bad in the respect that with mp4 as a container you don't need them since the same effect can be achieved via a VFR (Variable Frame Rate).

DivX I guess doesn't use realy N-VOP's. I could probably do a build of XviD with N-VOP's disabled so that even if two frames are 100% identical it doesn't drop one. But I have never had such issues on my player.

[FulciLives]

I could probably do a build of XviD with N-VOP's disabled so that even if two frames are 100% identical it doesn't drop one. But I have never had such issues on my player.

For those that have the Philips DVP-642 that would be a godsend.

Yes I know everyone makes fun of the ESS chipset but let's face it ... most people with a MPEG-4 player have the Philips DVP-642

So it only makes sense to have a way to make stuff work on it.

Since autoGK is making XivD videos that sometimes have NO VOP-Frames but sometimes have only 1 or 2 N-VOP frames per "full length" movie then surely there is a way to make it with NO N-VOP frames at all at all times.

- John "FulciLives" Coleman

[LisaB]

Hey Fulci,

Yep, that's my guide. It's funny how when you let stuff loose on the internet that it turns up in the darndest places

So I wrote the guide long after I started this thread, so the info in my guide should be better.

I have never actually managed to encode an avi with N-VOP's, so my observations and theories regarding N-VOP's are the least tested.

I do believe, however, that if you want to have N-Vop's, then you need to set the "dropped frame ratio" to a non-zero value. That is in the "advanced options" of the XviD configuration. Even if you set this to a non-zero value, the XviD will only put N-Vop's in your output if it finds two consecutive frames that are extremely similar.

Obviously, if you have a 642, then you *do not* want real N-Vop's. Well, as long as you set "dropped frame ratio" to 0, then you should never get an N-VOP.

Now, I tried to purposefully create an AVI with N-Vop's and couldn't. I think the reason is that only certain versions of XviD have this feature implemented. So, if you don't have the right XviD version, you can set a large "dropped frame ratio", use a source with plenty of duplicate frames, and *still* end up without any N-Vop's.

The idea with "dropped frame ratio" is that it can save some space on sources with lots of dupe frames (like anime), because it inserts a dummy frame (N-VOP) in place...which I guess just says "repeat previous frame" to the decoder.

I think you're making too much of the bitrate spike thing. One thing I have discovered since writing that guide is that the 642 can't quite handle 640 width if the avi is full-screen. That is why I encode all widescreen vids with 640 width, and all fullscreen vids with 608 width. At first, I was thinking the whole problem was bitrate, but this seems not to be the case. In fact, I can encode vids with bitrate of at least 3000, and still not see problems....but if I encode a vid to 640x464, even with a bitrate of 1000, I get problems! Keep in mind that I use b-frames with the default settings (i.e., max conseq. = 2)

Anyway, I've never used AutoGK because I "don't trust those durned automatic things". I use regular GK to setup my AVS files, and then use VDubMod to encode the AVI's.

[LisaB]

If your video only has one n-vop at the start, then just remux to fix the audio synch! For 23.976 fps, you already know the adjust will be 42 ms.

[KiwiKid]

Hi LisaB
I have been following your posts with great interest. As an owner of a 642 I have also encountered problematic AVIs. I had a lot of trouble with one containing many N-VOPs - I thought the audio was encoded wrong until I read your post. I had tried AutoGK,Dr DIVX and DIVX Converter but only DIVX Converter recoded correctly without actually dropping any of the N-VOPs. I still had to adjust the audio 500ms though. I have been impressed with the quality of the Converter but I have encountered the mysterious "Insufficient Space" error. I would like to be able to rely on one program to get the recodes done so I am hoping you could provide some more details on how you do it. Any help would be greatly appreciated.

[celtic_druid]

@LisaB, as I said setting the framedrop ratio to 0 won't stop XviD from inserting N-VOP's if you have b frames disabled.

0, plus bframes should mean no N-VOP's. In my tests I couldn't get XviD to insert N-VOP's in such a case even with 100 identical frames.

[FulciLives]

Well I just used AutoGK with DivX 6.x and it worked a charm ... no N-VOP frames and the resulting AVI (about 1400MB) played fine from a DVD-R disc. Same movie, using AutoGK and Xvid had 1 N-VOP frame.

BTW I have one 4:3 full frame DVD (NIGHT GALLERY TV series) that I backed up using AutoGK and Xvid and it has no N-VOP frames and I used 640x480 and it plays back fine from a DVD-R disc (again the file was about 1400MB). The "movie" (it was the pilot) was about a good 90 minutes long.

My Philips DVP-642 is rather new ... just bought it at Walmart and it comes in one of those new mostly white boxes.

- John "FulciLives" Coleman

[celtic_druid]

As I said I don't think DivX does real N-VOP's so you should be safe everytime.

[FulciLives]

As I said I don't think DivX does real N-VOP's so you should be safe everytime.

On my computer monitor the Xvid version looked ever-so-slightly better ... sharper I would say ... than the DivX but the DivX looked really damn good on my TV playing it back on the Philips DVP-642 so from now on I think I will just stick with DivX and thus avoid the whole N-VOP issue.

- John "FulciLives" Coleman

[mgh]

Use latest build of xvid listed in videohelp tools -first hit defaults button-then select HT NTSC or HT PAL profile depending on your vid. Adjust only bitrateand select single pass, first or second pass. The video will not have problems with the philips 642. For good quality playback on TV use 0.2 to 0.25 bits/pixel.

Nice to know that even gurus get puzzled sometimes

[celtic_druid]

Video help tools has XviD v1.0.3 listed which doesn't have DXN profiles. You need a 1.1.x build for that.