Max bitrate problems ?

[IanRC]

Hi all

I would be very grateful for some assistance in connection with max bitrate problems (I think). Firstly, am I correct in assuming that the lower the bitrate available to the video stream the worse the video quality (and therefore one should seek to maximise the bitrate available to the video stream).

I have encoded a couple of movies (Moulin Rouge and Spiderman) using CCE (Robshot method) and then mastered DVDs with DVDMaestro. The problems are as follows:


the audio soundtracks keep going mute at random intervals

the picture breaks up (pixalation ?)


Are these signs of exceeding the maximum bitrates ? - I am getting the buffer underflow warning after compiling. The weird thing is I re-encoded using a lower max bitrate (down from 9800 to 9500) and if anything the problem seemed to get worse.

Alternatively is this likely to be a problem with the discs themselves, in particular do DVD-RW and DVD+RW discs deteriorate if you record on them more than once. The discs are good quality Sony and Imation discs so I don't think that this is the problem.

Grateful for any assistance that can be offered as this is driving me nuts - I will know the films off by heart soon.

Thanks

IRC

[oddyseus]

Hi all

I would be very grateful for some assistance in connection with max bitrate problems (I think). Firstly, am I correct in assuming that the lower the bitrate available to the video stream the worse the video quality (and therefore one should seek to maximise the bitrate available to the video stream).U r assuming correct

the audio soundtracks keep going mute at random intervals
the picture breaks up (pixalation ?)If the picture breaks up, ie stutters, it is indeed a syptom of high bitrate. Maestro is pointing this after the end of compiling the title set.
Pixelation is a completly different issue where picture breaks up in little squares in scenes with heavy motion. This is a low bitrate syptom.

I am getting the buffer underflow warning after compiling. The weird thing is I re-encoded using a lower max bitrate (down from 9800 to 9500) and if anything the problem seemed to get worse.This is exactly the error u should get if u have exceeded that max allowed combined for audio/video/subs bitrate of 10.08mbs.
This thread (http://forum.doom9.org/showthread.php?s=&threadid=53191&highlight=buffer+underflow) deals with this problem.

Alternatively is this likely to be a problem with the discs themselves, in particular do DVD-RW and DVD+RW discs deteriorate if you record on them more than once. The discs are good quality Sony and Imation discs so I don't think that this is the problem.Pixelation can indeed be caused by faulty or deteriorated media. Theoritacally speaking dvd-r has a 1000 times burn/erase cycle. I doubt if anyone can reach this limit with reasonable use of the disc. However storage conditions and poor handling can deteriorate media's performance.

[IanRC]

Thanks Oddyseus

I guess I will just have to persevere, reducing the bitrate allocated to the video stream whilst encoding with CCE. On a related subject I have tended not to use the MBR second pass option in CCE because one pass VBR is giving me the right size files. The second pass is not required in this case according to the guide, but I wonder if the failure to use it may be contributing to the other problems I am experiencing.

Thanks again.

IRC

[oddyseus]

MBR is usefull if u want to finetune the final output size and pinpointing the trouble areas in the video that need this little bitrate more than others. It wont fiddle with your max setting and wont solve any problems related to the max bitrate.

I would suggest to lower the max bitrate to 9000 if u r dealing with one angle, 8000 if u have two angles. Max for a 4 angle video is 6500.

U don't have any dts audio in it, do u?

[IanRC]

Looks like you could be spot on.

I was just looking at the size of the streams and there is a DTS stream that drops a 755k load on the bitstream. Taking just that and the 448k DD audio leaves only circa 9,600 for the video. Unfortunately I am at this moment running a compilation with another three (small) audio streams. I guess it is not going to work.

Thanks again for the help, at least I now know how to tackle the problem.

IRC

[manono]

Hi-

Sorry to butt in. I've never made a DVD-R in my life, but a little quick addition (755+448), allows much less than max 9,600 for the video. Did you mean 8600? And please correct me, oddyseus, if I'm wrong.

[oddyseus]

Manono u r right.

Max combined bitrate is 10.08mbs, if u subtract dts and ac3 from it u ll end with 8.87mbs that still has to accomodate subs if any r present plus the muxing and control streams.
This leaves 8600max. I wouldn't be surprised if it is actually a bit lower. I would encode to 8300 just to be on the safe side.

[IanRC]

Thanks for your help guys.

One further question if I may. I encoded a movie using CCE with a max bitrate of 9,500kbps. I then had to use pulldown in order for DVDMaestro to accept it.

I then dragged and dropped the pulled video stream onto the DVDMaestro timeline and right clicked on properties. To my surprise this showed a bitrate of 9800000.

Does this mean that CCE did not properly apply the limit or is this just bug in DVDMaestro, I couldn't find anything in the DVDMaestro manual about this problem.

Ta

IRC

[oddyseus]

Not at all. This is the nomimal bitrate of the video stream as it has been set by pulldown and has nothing to do with the actual bitrate. In fact u can set it practically at any value without affecting the quality or the playback ability of the video.