Guides

Decisions, Decisions, Decisions

So now that we've collected a bunch of information about our source files it's time to use it to formulate a plan to prepare them to be DVD authoring assets. Before we actually do that though, we need to consider how we're doing for space. The total size of all files as they are now is approximately 4,682MB. We know our MPEG-4 video wil have to be encoded to MPEG-2, and that The 39 steps will need to be encoded again because it's at the wrong resolution. Realistically we can probably expect a DVD that's at least 6GB. Assuming a dual layer blank that should be fine.

NTSC

Although most of our extras don't have to be re-encoded, I'd like this DVD to look as good as possible if played in a progressive scan player with a progressive display. Due to a variety of different techniques used by players to deinterlace, our best bet for this is recovering the original film frames ourselves through a process called Inverse Telecine (IVTC). This will require re-encoding, which I noted at the beginning of the guide is something we'd like to avoid. However, I feel the quality gain from proper progressive frames is worth a small amount of quality loss from re-encoding.

Pulldown

Since our video with recovered film frames will have a framerate of 23.976fps it will need to have pulldown (RFF) flags added so fields will be duplicated, resulting in NTSC's 29.97fps. The 39 Steps has been sped up to PAL framerate (25fps) so conventional wisdom would suggest it should be slowed down to 23.976fps, requiring the audio to be resampled at the slower speed, allowing standard pulldown to be applied. Instead we're going to use non-standard pulldown to convert 25fps progressive video to 29.97fps interlaced.

Aspect Ratio

Without knowing more about where our source files came from it's hard to know for sure what the original AR was. If they were commercially transferred from film to digital, and it appears that they were, they would most likely have been given an AR of 1.33 to match television signals. Our best bet is to simply let our encoder assume 1.33 and output a file that matches it. If the files with a 1.36 AR actually contain the original film frames (whch would have an AR of 1.37) a better method would be to remove the correct number of pixels on each side and then resize to DVD resolution. However I suspect that isn't the case, so I'll just assume it can just be changed.

Audio

Some of the audio is encoded as AC-3, while some is MPA or AAC. By converting it all to AC-3 we'll have our mandatory audio format.

PAL

Making a PAL DVD from this will be a little more work because of how most of the extras were encoded. If they had been encoded as original (film) frames at 23.976fps with pulldown flags added, simply speeding them up. However, since the telecine pattern is encoded in them, they'll need an Inverse Telecine (IVTC) operation performed to recover the original film frames.

Resolution

The resolution for all files will need to be increased to Full D1, which for PAL means 720x576.

Framerate

Only one of our source, The 39 Steps has PAL's 25fps framerate. While it will only have to be resized to 720x576, the other video will also need to be sped up to 25fps. This will require resampling the audio after the speed increase.

Aspect Ratio

Without knowing more about where our source files came from it's hard to know for sure what the original AR was. If they were commercially transferred from film to digital, and it appears that they were, they would most likely have been given an AR of 1.33 to match television signals. Our best bet is to simply let our encoder assume 1.33 and output a file that matches it. If the files with a 1.36 AR actually contain the original film frames (whch would have an AR of 1.37) a better method would be to remove the correct number of pixels on each side and then resize to DVD resolution. However I suspect that isn't the case, so I'll just assume it can just be changed.

Audio

In order to resample audio, it will have to be decoded from whatever lossy format it's already in. Afterwards we'll encode everything to AC-3 for best player support. Unlike NTSC it is legal to have MPA as the sole audio stream. However, I still recommend encoding to AC-3.

Next: Preparing Audio

Version History

v1.0 2007.08.21 by Vurbal
v1.1.0 2007.08.23 by VurbalTable of Contents

1. Introduction
2. Requirements for DVD Compliance
3. Analysis
4. Interpreting The Results