Posted: Sat 13 Mar 2004, 21:39 Post subject: Suggestions Desired for Compression of an Advanced Slideshow
With Video Vegas LE 3.0 I have created a 5.5 minute photograph slideshow set to music. All of the photographs are shown with some combination of pans and zooms. The original photographs come from a dSLR camera, so they are very high quality and I want this to show in the final DVD. I am rendering the video as uncompressed video in Video Vegas and then using TMPGEnc for the MPEG2 encoding. Right now I am just experimenting with a small 10 second clip to try and get the compression settings right. I am using a CBR of 8000kbps and have found that changing some of the I, P, and B GOP settings make large differences. I found that raising the number of P pictures to 7 (from 1) drastically improved the quality. However, I can still tell the difference between the MPEG2 and the uncompressed video. As closely as possible I want to duplicate the uncompressed video. As long as the resulting MPEG2 can be burned to DVD and played on a standard DVD player, I have no real limitations regarding file size.
I have read the compression FAQ on this site, but I still feel uneducated regarding some of the finer points of I, P, and B GOP settings. I would really appreciate any help on recommended settings to that I don't have to continue learning via trial and error. Thanks!
Joined: 04 Feb 2003 Posts: 587 Location: Lisboa, Portugal
Posted: Mon 15 Mar 2004, 17:46 Post subject:
Using a lot of I pictures would give you great quality if you didn't have a bitrate limit. Unfortunately, DVD is limited to 9800 Kb/s (and you really shouldn't use more than 8000 for video, if you want it to be compatible with older players).
I pictures give you the best quality, but need very high bitrates (much higher than DVD supports). P pictures are slightly inferior in quality (especially if the image moves very fast) but need less bits. B pictures are worse than P pictures, but need much less bits, so they're good when you are limited to a lower bitrate.
If you use IP\, the compressor doesn't really have anywhere it can "save" bits, so there aren't enough to make the I pictures look good. Since P pictures are based on the previous I picture, this makes everything look terrible.
Fast motion sometimes looks better with IPPPP\, but if each frame is similar to the previous one, long sequences of P pictures will look fine, and save some bits that can be used to improve the I pictures. So IPPPPPPP\ or even IPPPPPPPPPPPPPP\ are good GOPs for 8000 Kb/s.
So that's probably as good as it gets. If your pans and zooms are reasonably slow, you can probably increase the number of P pictures (to 14, for example) and get slightly better quality.
But it will never look quite as good as the original (uncompressed, high-resolution) stills. Remember, DVD is meant for the same market as VHS; it's not a professional video format.
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