I too think there has been a little exaggerating going on in this thread.
Perhaps some of you should go to Doom9 or Doom10 and read some threads by Dark Shikari (x264 developer), on how constant quality x264 encoding actually works. Many knowledgeable people maintain that a constant rate factor (crf ) of ~18 or a bit lower approaches "transparency" at tune film presets. For you people with superhuman vision and enormous displays, let's put that at crf 17. I defy you to tell the difference between a pressed BD and a crf 17 re-encode reliably, during normal viewing. Normal viewing, that is.
Let's stipulate that yes, any encode/re-encode to a lossy codec will necessarily degrade picture quality, however slightly. And that includes the first one, from master. Also, the bitrate required is source-dependent. A grainy movie like Saving Private Ryan needs bucketloads of bitrate, whereas clean animation like, say, Wall-E needs much less. That's why the final output size of a crf encode is unpredictable, apart from the very general rule that a grainy/noisy source needs more bitrate than a clean one. Encoding the movie Saving Private Ryan at crf 17 will save essentially no space at all, while Wall-E will show a significant file size reduction. And that is despite the fact that main movie on the Wall-E Blu-Ray is considerably smaller than BD25 size. (Which allowed them to stuff all those extras on the disc.)
As has been hinted at, H.264 is far more efficient than MPEG2, and degrades more "gracefully" as bitrate is reduced. But the principle is the same: I,P,B frames in GOPs (Group Of Pictures). Keyframe (I), progressive frames (P) that reference the frame preceding, and bi-directional frames (B) that reference preceding and succeeding frames. Only the keyframe has the full information, the other types use motion vectors and what amounts to error correction. If a re-encode is not too aggressive (~crf 17), it may only reduce some of the redundant error correction. Yes, I've oversimplified, but there you are. Most discriminating viewers will find a crf 18-19 encode perfectly acceptable.
Edited by fritzi93 - 1/3/13 at 7:15pm
Perhaps some of you should go to Doom9 or Doom10 and read some threads by Dark Shikari (x264 developer), on how constant quality x264 encoding actually works. Many knowledgeable people maintain that a constant rate factor (crf ) of ~18 or a bit lower approaches "transparency" at tune film presets. For you people with superhuman vision and enormous displays, let's put that at crf 17. I defy you to tell the difference between a pressed BD and a crf 17 re-encode reliably, during normal viewing. Normal viewing, that is.
Let's stipulate that yes, any encode/re-encode to a lossy codec will necessarily degrade picture quality, however slightly. And that includes the first one, from master. Also, the bitrate required is source-dependent. A grainy movie like Saving Private Ryan needs bucketloads of bitrate, whereas clean animation like, say, Wall-E needs much less. That's why the final output size of a crf encode is unpredictable, apart from the very general rule that a grainy/noisy source needs more bitrate than a clean one. Encoding the movie Saving Private Ryan at crf 17 will save essentially no space at all, while Wall-E will show a significant file size reduction. And that is despite the fact that main movie on the Wall-E Blu-Ray is considerably smaller than BD25 size. (Which allowed them to stuff all those extras on the disc.)
As has been hinted at, H.264 is far more efficient than MPEG2, and degrades more "gracefully" as bitrate is reduced. But the principle is the same: I,P,B frames in GOPs (Group Of Pictures). Keyframe (I), progressive frames (P) that reference the frame preceding, and bi-directional frames (B) that reference preceding and succeeding frames. Only the keyframe has the full information, the other types use motion vectors and what amounts to error correction. If a re-encode is not too aggressive (~crf 17), it may only reduce some of the redundant error correction. Yes, I've oversimplified, but there you are. Most discriminating viewers will find a crf 18-19 encode perfectly acceptable.
Edited by fritzi93 - 1/3/13 at 7:15pm
). Like I said in my earlier posts, I generally don't bother to compress nowadays because storage is so cheap and I would rather not take the time, but bd rebuilder does an excellent job of compressing bd down should the need arise. I would love to be a fly on the wall with some of these posters claiming huge differences on a double blind test of a moderately compressed (say a 35gb movie file down to 20ish gb's) movie shown on a 65"+ display vs the original blu ray file on the same display. I can already invision them with their noses right up against the set during a paused frame saying "yup, theres a little smear there, must be the copmpressed one" lol....
