Why is MPEG getting re-transcoded in DVD authoring?

[Brad Bailey]

I have MPEG 2 files created from TV using Beyond TV (4.1) program and Hauppauge PVR250BTV capture card. My goal is to be able to both edit these then burn them into projects with the least need for any further compressing (loss). The BTV capture settings are at “Best – DVD quality”… I edited in VideoReDo which is clearly not to be re-encoding them… so why when I author / burn as DVD using Sonic MyDVD (6.1) does it go into a long transcoding video process (1 hour or more for an hour of video). I had hoped that by maintaining an appropriate MPEG 2 format I could avoid the need for retranscoding. Any insights or help with settings that could avoid this would be greatly appreciated.

[guns1inger]

There are number or things that might set off a transcode - incorrect resolution, incorrect resolution for the format, incorrect framerate, incorrect framerate for the format, incorrect GOP sizes amongst other things.

Also, some lower end (and even higher end) software has been know to just transcode of it's own accord, or transcode by default. Check the menus and preferences for an optiont to turn off transcoding for compliant material. If you don't have this option, ditch the software and get something that works properly.

[FulciLives]

Try using a DVD authoring program that does not re-encode or transcode. Popular examples would be TMPGEnc DVD Author for simplicity of use or one of the DVD-Lab versions for someone that needs more flexibility and are willing to learn to use that flexibility.

- John "FulciLives" Coleman

[redwudz]

You might want to check the video before you author it to see if it is DVD compliant. The latest version of Gspot should give you some info. If you look to the upper left in 'What is' DVD you will see the DVD specification. <<<<<<

If it seems to be in spec, it may be like guns1inger mentioned that your authoring program is re-encoding by default. Try a trial version of TMPGEnc DVD Author. AFAIK, the only thing it will change is the audio bitrate if it's 44K instead of 48K. It will reject the video before it modifies it.

[trhouse]

I have Sonic MyDVD 6.0. It does not re-encode unless the input is not dvd compliant or if you edit with it. Trimming off the ends is ok. Adding chapters and menus does not cause re-encoding.

I would suggest a simple test. Capture about 10 seconds of video with your card and send it to MyDVD and without any edits or authoring, tell it to burn. If it re-encodes, the source is probably not compliant.

[Brad Bailey]

Heres what I tried:

File being tested:
Via Video Inspector -
File Size : 4.42 Gb.

[Movie]
Valid : Yes [MPEG]
Duration : 01:26:21
Movie complete : Yes

[Video]
Resolution : 720x480
Codec : MPEG 2
FPS : 29.97
BitRate : 6836 Kbps
Quality Factor : 0.68 b/px

[Audio]
Codec : MPEG 1 Layer 2
Number of channels : 2
Sample Rate : 48000 Hz
BitRate : 128 Kbps


GSPOT shoes Cinemaster codec as choice to encode / decode when it does render.

What I don't know is how to find out info on GOP structure... I know nothing about that. But Sonic notes that a requirement for MPEG in their software is
I Frames: 1
P frames: 5
B frames" 2

I did a short test of enedited MPEG and in author burn it did NOT SHOW transcoding process (and was long enough to have shown),,, I think audio showed briefly. Same MPEGS edited in VideoReDo definitely transcoded.

Frustratingly... the burn failed itself... at the start of writing files.

1. Even though the editor does not re-encode... could the edits trigger the re-encode in Sonic?
2. Is the GOP structure the type of thing that could get changed in that editing process (removing commercial breaks)? How can I check the GOP structure?

Thanks.

Brad

[trhouse]

I have not used VideoRedo but if it can do a frame accurate edit, then it is possible the GOP structure is altered. That is one reason some programs like TMPGEnc DVD Author do GOP level edits. It might be easier for you to download the free trial version of TDA and try it. I have used it and imported its output to MyDVD and have not had any problem.

Mpeg1, layer 2 audio is not compliant in NTSC dvd standard which is why it is being re-encoded.

[guns1inger]

You could try using restream to re-write the headers and see if that smooths thing out.

[thecoalman]

[Audio]
Codec : MPEG 1 Layer 2
Number of channels : 2
Sample Rate : 48000 Hz
BitRate : 128 Kbps

This could possibly be the culprit... I'm not familiar with the software you're using but if what the software percieves as non-compliant triggers the entire clip to be reencoded that could be it even if it's just the audio portion. Although mpeg audio will work in most NTSC players, probably any new machine, it won't work in some older models....

Try a test clip with WAV.

Edit: what trhouse siad, I was working off a window I loaded this afternoon... :P

[trhouse]

MyDVD will transcode only the audio if it is not LPCM or AC3. The audio alone will not cause the video to be transcoded.

[shiet]

stupid adobe encore will reencode a dvd compliant mpeg

[Brad Bailey]

Yes Sonic MyDVD appears to NOT transcode video if audio alone needs it... as noted above when I tried a short test of same BTV4 / Hauppauge encoded MPEG2 that I did NOT edit via VideoRedo and it did NOT show video transcoding.
So... about the GOP structure... how can it be seen or assessed so I can see if it fits the Sonic requirements and if it's being changed via editing?

[iant]

Hi,
Just to throw my two cents worth in, I'll suggest the following.
Use VideoRedo edit and save out as separate streams as a saved MPG from VideoRedo is not usually compliant.
Use Imago muxer (Freeware) to remux file. Guaranteed compliant. Never had a problem with it.
Use Gui For DVDauthor (Freeware) to author your disc. (Bit hard to come to grips with initially as you really must read the instructions. But once you do...easy and effective. ) It will only author if everything is %100 compliant and will let you know which bit is causing you the problem if it's not compliant. Can't get fairer than that.

Works beautifully for me anyway.

Have fun,
Ian

[trhouse]

Import your mpeg file into freeware VirtualDubMod. It will show and identify each frame as an I, P, or B frame.

[ronnylov]

If myDVD converts the audio to LPCM then it will be too big to fit on one single layer DVD so it may then also transcode the video?

You are close to the maximum size for a single layer disc without any transcoding. A 4.42 GB file won't fit on a single layer DVD. The maximum size is around 4.38 GB.