Video underflow when muxxing with BBMpeg, help needed.

[MaX_NormaL]

Hi

I often used to get these when muxxing my vbr mpeg2 video but since I moved to cbr and finding good settings in BBmpeg I have never had it since till now.

It reported one underflow in first disc of 3 disc svcd and advised me to lower video bitrate which was cbr 2450. Audio was 192 kbps btw. Would this solve it?

I watched the file in WMP and noticed no problems whatsoever but they may show if I burn it.

I have always used the same settings to mux svcd which are :

VBR - Checked (dunno what this does) even though I encode at cbr?
Write program end code
Add SVCD Scan Offsets

Computed Bitrate - use max
Forced mux rate = 0
Pack 2324 - Packet = 1

Everything else is left as when I installed it. Is this ok for settings and should I worry about the 1 undeflow?

Any help would be great, thanks

[MaX_NormaL]

OK I lowered the video bitrate and it reported MORE errors LOL.

ps CCE is doing the video.

[adam]

I a little confused. Are you making a SVCD? Because with the SVCD preset you can't set the Computed Bitrate option, that is only available in mpeg2 preset. If your making a SVCD then use the SVCD preset.

As for underflows, they will not occur with forced mux rate at 0, or at least they shouldn't.

CBR means constant bitrate but that is a misnomer. There is no such thing as constant bitrate because there are always bitrate spikes. If you encode at 2.5mbits cbr you may have bitrate spikes as high as 4mbits, but these are so brief they almost never cause any problems. I think your problem may be that you have computed bitrate set to max bitrate, which like I said doesnt even apply to bbmpeg's SVCD multiplexing. My guess is that these bitrate spikes are making it appear that your bitrate is much higher than it is, making bbmpeg think there are underflows, since your computed bitrate is only looking at the max bitrate.

When multiplexing SVCD in bbmpeg always do this...First just load the SVCD preset. You can uncheck SVCD scan offsets and allign sequence headers if you want, it may or may not affect playback, but other than that leave everything else alone. If you get underflows during multiplexing then cancel it and set the forced mux rate to 0. This should eliminate all underflows. Don't use forced mux rate or 0 (automatic) unless you have to because it can make the filesize larger.

[MaX_NormaL]

Your confused?

Thanks, yes I am trying to make an svcd. Like I said I have never had any probs this way which is why I am stumped!

I am using BBMpeg 124b18 under xp (with patch) and tried what you said about restoring defaults but as soon as I set force mux rate to 0 then the 'unused' in computed bitrate auto switches to 'use max' when I go to one of the other fields ie - General Settings and come back to it. The other option is 'use avg'. I also cannot uncheck align sequence header.

I understand about the cbr as I noticed cce fluctuate between 2.4 - 2.5 when set to 2450.

I will try and mess about with it and try some other versions and let you know how I get on.

ps I always use force mux = 0 with no prob ever, are you saying I shouldn't really?

Thanks a lot m8.

[adam]

Thats not a stable release of bbmpeg. Use 1.24 beta 13 instead, that alone may solve all your problems. I don't use XP so I can only hope that this release of bbmpeg works on it. If you are forced to continue using beta 18 than try setting computed bitrate to avg, that makes more sense, especially for CBR.

I just want to make sure cause it was a little unclear. You are using the SVCD preset not the MPEG2 preset right? Maybe its just different from one version of bbmpeg to the next but with SVCD preset you cannot set the computed bitrate and you can uncheck "align sequence headers" but only after you have first unchecked add SVCD scan offsets. You either use them both or none at all.

forced mux rate of 0 is not necessarily bad. It just lets bbmpeg set whatever mux rate is appropriate for your bitrate, sometimes with additional overhead. The SVCD preset of 6972 will always work if your total bitrate does not exceed the limits set by the SVCD standard, ~2.778mbits. With forced mux rate of 0 your filesize might be a little larger than it needs to be.

[MaX_NormaL]

Thanks again,

I only understand it to a certain extent but I thought it must be the version as I only recently replaced it from b13

I got this report from using default settings (SVCD Preset as usual) : Sorry for this


Scanning video stream for pictures ...
Found 136544 picture headers.
Video stream information
Stream length : 1672664004
Total time (seconds) : 5461
Sequence start : 11558
Sequence end : 1
No. Pictures : 136544
No. Groups : 11558
No. I Frames : 11558 avg. size 40916 bytes
No. P Frames : 34495 avg. size 16508 bytes
No. B Frames : 90491 avg. size 6967 bytes
No. D Frames : 0 avg. size 0 bytes
Horizontal size : 480
Vertical size : 576
Aspect ratio : 0.7031
Picture rate : 25.000 frames/sec
Bit rate : 306250 bytes/sec (2450000 bits/sec)
Computed avg rate : 307500 bytes/sec (2460000 bits/sec)
Computed max rate : 937150 bytes/sec (7497200 bits/sec)
Vbv buffer size : 229376 bytes
CSPF : 0

Scanning audio stream for access units information
Found 227580 audio frame headers.
MPEG audio stream information
Stream length : 131086080
Syncwords : 227580
Frames : 227580 size 576 bytes
Frames : 0 size 577 bytes
Layer : 2
CRC checksums : yes
Bit rate : 24000 bytes/sec (192 kbit/sec)
Frequency : 48.0 kHz
Mode : 0 stereo
Mode extension : 0
Copyright bit : 0 no copyright
Original/Copy : 0 copy
Emphasis : 0 none
NOTE: Mux rate may be too low for data rate, watch for PTS/DTS underflows.

Multiplexing information
Video stream data rate : 937150 bytes/sec (7497200 bits/sec)
Audio stream 1 data rate : 24000 bytes/sec (192000 bits/sec)
Total data rate : 348600 bytes/sec (2788800 bits/sec)

Multiplexing file c:\temp\ring_01\ring_01.mpg
video PTS (1615460.00ms) underflow at pack 235001 by 13.33ms
video PTS (1615500.00ms) underflow at pack 235009 by 26.67ms
video DTS (1615540.00ms) underflow at pack 235018 by 46.67ms
video PTS (1615580.00ms) underflow at pack 235028 by 73.33ms
video PTS (1615620.00ms) underflow at pack 235036 by 86.67ms
video DTS (1615660.00ms) underflow at pack 235043 by 93.33ms

with about 20 more errors after that if that helps, and this one with my normal settings :

Scanning video stream for pictures ...
Found 136544 picture headers.
Video stream information
Stream length : 1672664004
Total time (seconds) : 5461
Sequence start : 11558
Sequence end : 1
No. Pictures : 136544
No. Groups : 11558
No. I Frames : 11558 avg. size 40916 bytes
No. P Frames : 34495 avg. size 16508 bytes
No. B Frames : 90491 avg. size 6967 bytes
No. D Frames : 0 avg. size 0 bytes
Horizontal size : 480
Vertical size : 576
Aspect ratio : 0.7031
Picture rate : 25.000 frames/sec
Bit rate : 306250 bytes/sec (2450000 bits/sec)
Computed avg rate : 307500 bytes/sec (2460000 bits/sec)
Computed max rate : 937150 bytes/sec (7497200 bits/sec)
Vbv buffer size : 229376 bytes
CSPF : 0

Scanning audio stream for access units information
Found 227580 audio frame headers.
MPEG audio stream information
Stream length : 131086080
Syncwords : 227580
Frames : 227580 size 576 bytes
Frames : 0 size 577 bytes
Layer : 2
CRC checksums : yes
Bit rate : 24000 bytes/sec (192 kbit/sec)
Frequency : 48.0 kHz
Mode : 0 stereo
Mode extension : 0
Copyright bit : 0 no copyright
Original/Copy : 0 copy
Emphasis : 0 none

Multiplexing information
Video stream data rate : 937150 bytes/sec (7497200 bits/sec)
Audio stream 1 data rate : 24000 bytes/sec (192000 bits/sec)
Overhead data rate : 15150 bytes/sec (121200 bits/sec)
Total data rate : 976300 bytes/sec (7810400 bits/sec)

Multiplexing file c:\temp\ring_01\ring_0100.mpg
video PTS (1963340.00ms) underflow at pack 285979 by 2.86ms
1 video underflows (SCR >= PTS or DTS)

NOTE: The resulting file may not play back correctly.
Try reducing the video bitrate or increasing the video and
audio startup delays.

Now I don't understand what all that means lol but it looks like force mux = 0 is the better option. Will get b13 again if I can find it and try again!.

Thanks for the help so far. :P

[MaX_NormaL]

Tried b13 with exact same result on both counts, I think there must be an error in the original dvd or in the encode with cce which can't be right?

[adam]

Something did go wrong with the encode. You apparantly have some really high bitrate spikes. The computed max rate of your video is way too high, thats what causing the problem. Otherwise your results are exactly what's to be expected. When your max bitrate exceeds the standard's limits you will get underflows unless you lower the mux rate low enough, but with such high bitrate spikes I suppose its still not enough to prevent at least that one underflow.

Like I said, due to bitrate spikes your max datarate for video stream is always going to be higher than your actual max bitrate setting in the encoder. So if you set 2.6mbits you may see 4mbits or so during bitrate spikes. But you have 7.5mbits and thats not normal.

Perhaps there is just something about your source which is causing CCE to throw too much bitrate at it. Maybe you should analyze the mpg in BitrateViewer and see where these spikes are. Sometimes CCE will use a ridiculously high bitrate during the last second or two of the film. If you see this then in bbmpeg you can trim off that last second or so, hopefully we are just talking about the credits.

I know it sounds silly but VBR with min, max, and avg all the same will be closer to "CBR" than an actual CBR setting will. One way or another you need to control these bitrate spikes.

Go ahead and try authoring the one mpg with only one underflow. Test it on your dvd player because an underflow won't necessarily manifest itself on a dvd player. Play it through and make sure its all in sync, and if so I'd just cut my losses on this particular source. If the problem persists with other sources well than you are going to need to isolate the problem.

[MaX_NormaL]

OK m8,

I will try that,

Thanks

[MaX_NormaL]

1 more question.

How would you recommend I encode then as I watched the vobs/avs and the prob is not present and it is in only 1 part of the whole film. Lasts roughly 6 secs. No big deal but if I can fix it then that would be cool.

vbr?

[BenStone101]

I'm getting the exact same errors (PTS/DTS Underflow) that Max is getting.

I'm trying to encode XVCD at 1800 bitrate. 1300 gave same error. What am I doing wrong?

I don't know a lot about what settings should be used in DVD2SVCD for VCD. I go to "Misc" and set ouput to "MPEG1". Under "Bitrate" I choose Max 1800, Min 1800 and MAX Avg 1800. Under Framserver I choose "Resize to" of "VCD (352x240/288). Are these all the settings that need to be checked for VCD?

Anyone else using DVD2SVCD successfully for XVCD? What are your settings?

[BenStone101]

Guess nobody is making XVCD with DVD2SVCD. Solved the problem partially by muxing the mpv and mp2 files created by DVD2SVCD manually. Increased the mux rate within bbmpeg and things worked out just fine.

Would be nice if we could change the mux rate for bbmpeg within DVD2SVCD.