TMPGenc Authoring 4: problem with incorrect bitrate

[bpchia]

Using TMPGenc Authoring 4 on Windows 7 64bit, i7 processor.

Video asset: MPEG-2 TS recorded from Australian DVB-T digital TV, 720x576

When I press "simulate" I get a warning that 3 elements of the video are not DVD compliant:
1. Video bitrate = 15000Kbps
2. GOP too long
3. Total bitrate = 15256Kbps (256Kbps MP-2 audio)

However, suspecting that Australian digital TV would not be broadcasting at 15Mbps, I opened the asset in MediaInfo, and found that the video bitrate was 6536Kbps, however the video bitrate (nominal) was 15Mbps.

Why is TMPGenc detecting the bitrate incorrectly (I'm not sure what "nominal" bitrate refers to, perhaps the maximum bitrate for that codec?)

I ignored the warnings and burned a DVD, the vob files had around about the 6500Kbps video bitrate, but not exactly the same as the original asset, does this mean reencoding has occurred or is it the nature of the TS vs vob format that changes the bitrate?

Many thanks.

[manono]

'Nominal Bitrate' is just a figure in a header and can be an accurate number for the max bitrate or can mean nothing at all. No authoring program will know the actual max bitrate until it authors, so you can safely ignore the TMPGEnc Authoring Works warning. This has been known for quite some time. I don't use the program and have no idea whether or not it's reencoding. I suspect it isn't and your bitrate reading program is reading them incorrectly. You might try Bitrate Viewer to check up on MediaInfo. Ordinarily, pure authoring might take 15 minutes or so. Reencoding followed by authoring takes much longer.

[bpchia]

Thanks. Will have to check, but when it was estimating the space required on the disc, it was much bigger than the size of the original file, like more than twice as big, indicating it is using the 15Mbps bitrate to calculate the size of the disc. I'm not at home so can't check if the actual size of the finished disc was the same as the estimated size...if the video was longer and resulted in an estimate of greater than 8.7GB (DL DVD) would it allow me to author?

Also still interested in whether the bitrate of video from the original MPEG-2 file is usually different from the bitrate of the resulting VOBs because of differences in the containers? Or my other idea is that the bitrate is different in each VOB that makes up a DVD because of VBR, meaning each segment has a slightly different bitrate. I'm just trying to work out whether there was an unnecessary reencode. I guess I could check by using SVCD2DVD to join the VOBs, should have same bitrate as source file, yes?

[manono]

If the GOPs are really too long, then it would have to reencode. You could check that by authoring using Muxman. It'll abort the authoring and warn you if it encounters GOPs that are too long (or a max bitrate that's too high). It'll never reencode anything. And, if true, you'll have no choice but to reencode if you want a DVD out of it. DVD video has much stricter rules than does MPG video.

[bpchia]

Great advice, thanks...so I mistakenly assumed that most SD digital TV in Australia is broadcast as DVD compliant MPEG-2 streams?

[manono]

DVD MPEG-2 video is a subset of MPEG-2 video and has GOP and max bitrate requirements that regular MPEG-2 video doesn't have. But, being an American who's never capped anything in his life, I couldn't begin to tell you what the Australian networks use. Perhaps someone else here can help.