Nebula DigiTV to DVD

[Grandpa Broon]

I'm trying to put my DigiTV MPG files on to DVD. Being an Adobe Premiere user for many years I decided to try Encore to author. The problem I'm having is after editing with VRD and importing into Encore, it mostly wants to re-encode the files.

I have had limited success by using various combinations of ProjectX, PVAStrumento, MPEG2Schnitt and Womble and now VRD.

Encore only accepts pure DVD compliant files with bitrates from 2mgb to 9mgb 720 x 576 25 fps PAL or 720 x 480 29.97 fps NTSC. The files I did yesterday had a bit rate of only 1.5mgb after using VRD even though they had an average of 2.1mgb before.

I don't know it this is the problem or not, has any other DigiTV user had this or a similar problem?

Regards David

[bitter_old_man]

Try using DVDPatcher to set the bitrate to a higher value. It doesn't actually change the bitrate, it just changes the value in the header. http://mitglied.lycos.de/dvdpatcher/

Barry

[DanR]

No need to use DVDPatcher. In VRD when you save a file simply click on Options in the file save dialog and you can change the header fields for bitrate and aspect ratio.

The files I did yesterday had a bit rate of only 1.5mgb after using VRD even though they had an average of 2.1mgb before. There are 4 different bitrates when dealing with an MPEG2 program stream.

1) The actual video bit rate.
2) The actual audio bit rate.
3) The program stream bit rate. This is the sum of audio and video bitrates plus program stream overhead like padding packets, system header packets, etc.
4) The MPEG2 sequence header bitrate. Most DVD authoring programs check this field although others do a quick calculation by dividing the video stream size by the program duration in sections. You can easily change the sequence header bitrate. Increasing the actual bitrate is harder.

There is a way for VRD to increase the actual bitrate is that is truely necessary. Let me know if the simple fix doesn't work.

[bitter_old_man]

I had never noticed that. Thanks for pointing that out, Dan.

Barry

[Grandpa Broon]

Thanks for your help, I'll try that tonight. Do you think changing it to about 3mgb should be okay?

David

[DanR]

Do you think changing it to about 3mgb should be okay?I honestly don't know. I've never seen that particular check, maybe its an Encore function. Most authoring programs check for too high a bit rate and you have to change the headers back to 9 Mbps or lower.

Another problem you might run into is long GOPs. Many of the DVB services (Sat and/or terrestrial) will create very long GOPs. DVDs are limited to 18 frame GOPs by definition, but most players don't have problems with longer ones. If Encore complains about the longer GOPs let me know. We are testing, with some users, a feature that will enable VideoReDo to shorten long GOPs automatically. It does some recoding and that adds time to the output, but its better than having to recode the entire program.

[Grandpa Broon]

DanR I've tried changing the bitrate to both 4 and 8 mgbs, it can't be that because it still wants to recode the whole mpeg. I've also tried splitting the mpeg into just using mpv files because it will always re-encode the audio file mp2 as it not DVD compliant, but again the same thing occurs.

Encore states: Imported files may or may not require transcoding. DVD-compliant assets typically do not require transcoding, while non-DVD-compliant assets do.

Any ideas?

David

[Grandpa Broon]

Update. I've found that some files I've captured from DigiTV will load direct into Encore without the need for transcoding. If I then edit them using VRD they again import with no problem and the bitrate I've noticed is 8mgb.

Other files even if they are 8mgb don't import either straight from DigiTV or edited with VRD. So maybe your GOP theory is correct in this case, how do I find out what the GOP size is?

David

[DanR]

Please email me at support@videoredo.com.

[DanR]

Hi David, Thanks for the upload, took a while, but I've found what the issue is. In a nutshell, your source file has some corruption. This isn't unusual when capturing off the air. Specifically at:07/08/04 08:12:53 00:01:01.23
07/08/04 08:12:53 00:01:01.24
07/08/04 08:12:54 00:01:36.07
There are missing frames in the GOP. These cause the "input sequence errors" being reported by VideoReDo. If VideoReDo detects missing P frames in a GOP then it will drop all frames after that. However, in this cause the missing frames were B frames and therefore, technically, the GOP is valid MPEG2. You can see that this assumption is wrong since the source picture is pixelated at this points. Note, if you cut these frames out of the file, it will import into Encore without transcoding.

I patched VideoReDo to re-write the temporal references, but this didn't solve the problem. There is obviously some internal corruption in the frames themselves that Encore is detecting.

There are a few solutions:
1) You can remove the offending frames with VideoReDo. We will probably have to put some additional info into the log file to let you know where the problems are.

2) You can use a different authoring program which is more forgiving of these problems. Most consumer oriented products aren't as stringent as Encore.

3) We can modify VideoReDo to improve detection of these situations. Just want to be sure we don't slow down processing too much.

[Grandpa Broon]

Thanks Dan, at least I now know what the problem is. I looked at those times on the video and you can see the dropout from the off air transmission. Of course I'm only editing the bits I don't want, not viewing the video.

As I've already said Nebula should have an update to their software on Monday. I'll contact them to see if they can give us a clue on when or if they can maybe have a fix for transmission corruption.

You've proved one thing it's not VideoReDo and if I choose to look at another DVD authoring program, I'll need to make sure it's not so pernickety about transmission errors. You can see the quality of the Mpeg is perfect though, but that's digital transmission for you.

Many thanks for your help
David

[DanR]

David,

I'll post build 244 shortly to the beta site: ftp://videoredo:videoredo@ftp.drdsystems.com/Betas/ This will have a fix that will log the missing frames to the log file. Open the log file with an editor and search for "Missing temporal refererence". Then you can edit out the area with the bad frames and Encore will load the file without transcoding. You might need to edit a few more frames than you think since we only report the error on the first frame of the GOP. I edited about 1 second in either direction just to be sure.

From what I can see the problem isn't a Nebula issue, but rather a temporary reception problem. Even DVB broadcasts aren't totally immune to interference. And, MPEG compression just makes things worse when there is dropped data.

As mentioned earlier, the "less expensive" consumer authoring programs like DVDLab, TMPGenc, Movie Factory, etc. will not care about these frame errors and will gladly author your DVDs without recoding.

[Grandpa Broon]

Dan,
I downloaded build 244 and edited another file with it which encore doesn't like but upon checking the log file I can't find any reference to "Missing temporal reference". The only word it that phrase I can find is temporal which is under "Frame Accurate Output Segment" both Video and Audio buffer predecoding load and GOP with no decoding required.

Cheers David

[DanR]

David, I think you might be stuck transcoding then with Encore. Its checking for something inside the MPEG2 stream that we aren't look for. A corrupt frame perhaps. This isn't something that VideoReDo looks for by default.

All I can suggest (other than using another program) is to see if you can isolate the section where the problem is by splitting your file into different segments. Then look for any visual clues. If you find them perhaps we can then replicate that search into VideoReDo.

One more thing. When you saved your file did you get any kind of stream errors reported. If you don't remember look at the log file summary. Steram errors preceeded by an "*".