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1st May 2017, 13:20 | #25881 | Link | |
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1st May 2017, 13:25 | #25882 | Link | |
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In telecining the video is actually 23.976fps (24fps)... and then pulldown flags are used to repeat fields and a new frame is generated for every 4 that actually exists during playback. In simple iVTC you can just reset those flags and the result comes out at the original frame rate. Telecining was created so that 24fps films could be easily converted to NTSC (29.97fps) for broadcast. Pulldown flags can also be used for other conversions (like PAL->NTSC or FILM->PAL) but you don't see that as often. Last edited by jdobbs; 1st May 2017 at 13:33. |
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1st May 2017, 21:41 | #25884 | Link | |
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1st May 2017, 23:16 | #25887 | Link | |
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The comparison is after decoding, i.e. after reconstruction of the original data. Last edited by Sharc; 1st May 2017 at 23:25. |
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2nd May 2017, 00:34 | #25888 | Link | |
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An example of a lossless compressor is a program that produces TIFF images. MPEG-2, H.264 or H.265 encoders are lossy. Take a look at: http://stackoverflow.com/questions/7...ss-video-codec Google lossless video encoder for more places to look. |
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2nd May 2017, 01:48 | #25891 | Link | |
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Example: You display the individual frames and save them with no encoding. Is that not lossless? When you look at the frames after encoding it will match bit-for-bit. Now -- use a lossless encoding method (there are hundreds of them) -- when it recreates the image it is EXACTLY THE SAME BIT-FOR-BIT PICTURE as the original. Just because you don't understand something doesn't make it any less a fact. H.264, MPEG-2, etc are not typically lossless. But there are many, many encoding methods that reduce size without losing a single bit. When you zip a file, do you expect the same output as input? Yes, because a zip uses lossless compression. There are also video codecs that use lossless compression methods that are designed specifically for video. Last edited by jdobbs; 2nd May 2017 at 02:00. |
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2nd May 2017, 01:49 | #25892 | Link |
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A true lossless encoding doesn't change the original. It is an EXACT duplicate. That's the whole purpose of lossless encoding -- it has no changes between encoding generations. You could do 9000 generations and have absolutely no difference between the original and the 900th encode. I'm not talking about "almost lossless" I mean lossless. You'd probably also find that the intermediate (compressed) files are exact duplicates as well.
Last edited by jdobbs; 2nd May 2017 at 02:02. |
2nd May 2017, 04:30 | #25895 | Link | ||
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I do understand what I am talking about. I just do not seem to be getting the info across. |
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2nd May 2017, 04:50 | #25896 | Link | |||||
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You will also note that X264 has a lossless mode.
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Last edited by jdobbs; 2nd May 2017 at 05:09. |
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2nd May 2017, 05:13 | #25897 | Link | |||
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The general rule of thumb is that when you re-encode, in order to reduce the added artifacts, is to have at least a 2:1 bitrate difference. That means if the resulting bitrate is 10 Mbps, the source bitrate needs to be 20 Mbps, or more. Keep in mind that 20 Mbps MPEG-2 video is approximately equal to H.264 video at 40 Mbps. So, recoding 10 Mbps MPEG-2 video to 10 Mbps MPEG-2 video does nothing but add digital artifacts. It will not result in a better looking video. Recoding from 10 Mbps MPEG-2 video to 10 Mbps H.264 video will result in fewer digital artifacts due to the 2:1 ratio and the better H.264 encoder. But, in all cases, the resultant recoded video will not look better than the original.[/QUOTE] Argh, that 2:1 stuff is still very confusing to me. I under 4:3 is SD and 16:9 is Letterbox or HD...but otherwise... I don't think I'll ever be a fan of MiB and Mbps. I still love and understand MB and KB or Kb. But I get your idea. :-)
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2nd May 2017, 05:18 | #25898 | Link |
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Okay!! Ahhh, yeah, this I have read and I have used them some years ago. They are uncompressed images. Thanks, JD, I knew I remembered correctly. Like BMP can be compressed or not, same as the old IFF format the Amiga used to name a couple. Indeed, very large. A lot of people don't know what compression is that I know. When I talk about it I'm usually asked what it means. I don't go into the details that MrVideo does but it gets it across.
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2nd May 2017, 06:06 | #25899 | Link |
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I admit that I didn't know that x264/ffmpeg had a lossless mode. I found the following in the ffmpeg site:
[code]Note that lossless output files will likely be huge, and most non-FFmpeg based players will not be able to decode lossless, so if compatibility or file size issues you should not use lossless. If you're looking for an output that is roughly "visually lossless" but not technically lossless use a -crf value of around 17 or 18 (you'll have to experiment to see which value is acceptable for you). It will likely be indistinguishable from the source and not result in a huge, possibly incompatible file like true lossless mode.[/quote] A lot of my wording indeed left a lot to be desired. Posts, not just by me, went astray from just changing the frame rate. I got the impression from posts that usable lossless output could be created for use with BD-RB, or at least desired. Yes, I did not include DVD sources. I limited responses to HD sources and should have said so. For files that members want to change from 29.97 to 23.976 that do not have pulldown flags (a majority of MPEG-2/H.264 HD videos), lossless recoding is not really a choice. The files will be way too large and more-than-likely not playable. Most certainly can't be burned to Blu-ray by BD-RB, as is. So, in a broad sense, the way HD videos are used with BD-RB, lossless recoding doesn't exist. As noted in the above quote, "visually lossless" output is very possible. I do it all the time. Time to move on. We've each made our points. |
2nd May 2017, 06:15 | #25900 | Link | |
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BTW, the 2:1 ratio tends to be moot at extremely high bit rates. |
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