No, this isn't about which is the best mpeg-2 encoder, it's about how to get the best out of any encoder. This isn't anything new, just stuff I've gleaned from a bit if searching and reading. To learn more you'll need to do your own but hopefully this will wet your appetite enough to go looking.
Firstly mpeg-2 encoding uses temporal compression, most probably know this and what it means but you need to keep that very much in mind when preparing or creating material for DVDs. But a further consideration is that the encoder(s) work on frames, not fields. The DVD spec was written primarily for movie release, starting with progressive scan material at 24fps.
To handle interlaced material the fields are merged into frames and the compression applied to the resulting frame. The player extracts the fields for output to the display device. However mpeg-2 works at 4:2:0 which looks like it's the same as PAL DV25 except the sampling matrix is different in mpeg-2 and remember the sampling is being done at the frame level. I'm suspecting this normally doesn't present any issues but still worth keeping in mind.
To get back to the issue of preparing material for temporal compression. This has been well covered in many places; the need for noise reduction is a vital area. Remember the encoder is looking at the difference between each pixel between frames, noise and dropouts are a nightmare for the encoder, they'll use up bandwidth big time. Wobbly shots are another big no no. But in general most well shot DV25 should encode fairly easily.
But there's another thing we can feed into the encoder, generated media, it can be still images or CGI.
Now this stuff can be at very high resolution, both in color sampling and in detail. If it's static then the encoder can do a great job. But what if we animate it, either in Vegas or in our CGI application. Lets look at a simple example. Create a vertical graduated fill in PS, save it in a lossless format, move the fill up one pixel in PS and save as a new frame. Now bring those two frames into Vegas and feed it to the encoder, Vegas feeds that at full res to the encoder, great you might think. Except we've now got two adjoining frames in which the value of every pixel has changed! Not a problem when rendering out to DV25 but a big ask for any mpeg-2 encoder. I'm suspecting using lossy compression to save the images would give the encoder much less stress. This is a pretty extreme example but it should show the issues you need to address, with almost all "natural" video the best quality input will give the best quality output, the same may not apply with generated media.
All compression systems, both for video and audio are based around how we see and hear. Normally they work just fine, however when we feed them things that aren't natural sources we need to be very careful lest we trip them up.
Some of what I've said here could have technical errors, anyone who knows better please feel free to correct me.
In any case my encoding workflow goes like this:
Check my source material for things I know will be hard to encode and fix them at the source, if I can't then at least I know not to blame the encoder. Check the encoded output, if I see something that looks bad address the issue at the source, you may well find that in some situations technically making your source worse will give a better result out of the encoder. Hollywood has way better encoders than most of us can afford and they still put a big effort into what goes into them.
With a moderate effort and without spending any more you should be able to get excellent results from the encoder that ships with Vegas. I'm not for a minute saying you cannot get better results with much more expensive encoders and if you have the budget then go for it. But even then the most capable encoders will give even better results if you prepare the material properly first.
Sorry for the long post, hope it at least gets a few heads thinking.
Bob.
Firstly mpeg-2 encoding uses temporal compression, most probably know this and what it means but you need to keep that very much in mind when preparing or creating material for DVDs. But a further consideration is that the encoder(s) work on frames, not fields. The DVD spec was written primarily for movie release, starting with progressive scan material at 24fps.
To handle interlaced material the fields are merged into frames and the compression applied to the resulting frame. The player extracts the fields for output to the display device. However mpeg-2 works at 4:2:0 which looks like it's the same as PAL DV25 except the sampling matrix is different in mpeg-2 and remember the sampling is being done at the frame level. I'm suspecting this normally doesn't present any issues but still worth keeping in mind.
To get back to the issue of preparing material for temporal compression. This has been well covered in many places; the need for noise reduction is a vital area. Remember the encoder is looking at the difference between each pixel between frames, noise and dropouts are a nightmare for the encoder, they'll use up bandwidth big time. Wobbly shots are another big no no. But in general most well shot DV25 should encode fairly easily.
But there's another thing we can feed into the encoder, generated media, it can be still images or CGI.
Now this stuff can be at very high resolution, both in color sampling and in detail. If it's static then the encoder can do a great job. But what if we animate it, either in Vegas or in our CGI application. Lets look at a simple example. Create a vertical graduated fill in PS, save it in a lossless format, move the fill up one pixel in PS and save as a new frame. Now bring those two frames into Vegas and feed it to the encoder, Vegas feeds that at full res to the encoder, great you might think. Except we've now got two adjoining frames in which the value of every pixel has changed! Not a problem when rendering out to DV25 but a big ask for any mpeg-2 encoder. I'm suspecting using lossy compression to save the images would give the encoder much less stress. This is a pretty extreme example but it should show the issues you need to address, with almost all "natural" video the best quality input will give the best quality output, the same may not apply with generated media.
All compression systems, both for video and audio are based around how we see and hear. Normally they work just fine, however when we feed them things that aren't natural sources we need to be very careful lest we trip them up.
Some of what I've said here could have technical errors, anyone who knows better please feel free to correct me.
In any case my encoding workflow goes like this:
Check my source material for things I know will be hard to encode and fix them at the source, if I can't then at least I know not to blame the encoder. Check the encoded output, if I see something that looks bad address the issue at the source, you may well find that in some situations technically making your source worse will give a better result out of the encoder. Hollywood has way better encoders than most of us can afford and they still put a big effort into what goes into them.
With a moderate effort and without spending any more you should be able to get excellent results from the encoder that ships with Vegas. I'm not for a minute saying you cannot get better results with much more expensive encoders and if you have the budget then go for it. But even then the most capable encoders will give even better results if you prepare the material properly first.
Sorry for the long post, hope it at least gets a few heads thinking.
Bob.