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In Reply to: RE: Looking for a way to record HD OTA broadcasts. posted by Jim Doyle on May 05, 2008 at 20:16:03
As I'm sure you know, people are downconverting HD to x264 and putting them in mkv containers. Typically, I see DVD-5 size, about 4.5 Gbytes, holding either 1 hour or 2 hours of originally HD material. Have you compared quality of these down conversions to the original pictures?
Follow Ups:
Hi there
Rather than "downconverting", converting OTA HDTV files in MPEG-2 to H.264/AVC is "transcoding". Downconverting implies somekind of reduction, presumably in spatial resolution. Transcoding implies no change in resolution, but converting from one codec to another (presumably with better compression but similar PQ).
Regards
Thanks for your answer. I am new to all this, having just gotten my first HD screen, a computer monitor. I have downloaded a couple of these x267 transcodes, one of which is amazing, the other which has some noticeable artifacts. I guess my question still applies. When these are turned into smaller files, has anyone compared to the original to see what might be lost?
Hi there
You have a good question, but I have not done any transcoding to H.264/AVC. One issue is that the PQ of TV shows varies and overall is not all that great. I've downconverted a few episodes of "Lost" and "House" to DVD resolution, and then upconverted for playback on a 720p CRT projector. The difference in PQ is not obvious to me. Some of the travel and nature shows on PBS have great PQ. If only the commercial broadcast networks matched that picture quality!
When transcoding, the digital artifacts will accummulate. And because these are lossy compression schemes, information is lost with each encoding. The concept of "perfect digital copying" does not apply here. Hope somebody can give you an answer.
Regards
But thanks for the clarity on "transcoding".
BTW I have an 8' screen and a JVC D-ILA, with which many (too many?) details can be seen.
clark
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