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  1. Member
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    Hi,
    I have read a fair bit on CBR, ABR, CRF and so on, but that applies to new rips.

    I have some existing rips in MPEG2 that are in CBR of pretty good 17Mbps. I want to convert them to H264.
    Would there be any reason not to choose the same 17Mbps CBR again for the conversion?
    Could I get any improvements anywhere in choosing VBR or CRF?
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  2. Mod Neophyte Super Moderator redwudz's Avatar
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    Just me, maybe, but I always use CBR. VBR may give you a bit smaller file size, but I seem to have less problematic playback with CBR and I have enough storage room.
    What H.264 conversion program are you using? I mostly use VidCoder, H.264/AC3 at 18.5 CQ.

    And welcome to our forums.
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  3. You can only decrease the qualitiy by re-encoding the existing MPEG2 files with h.264. If you go back the original sources you can get better quality at the same bitrate, the same quality at a much lower bitrate, or somewhere in between. If you recompress at the same bitrate the files will be the same size (aside from minor container overhead differences). Typically, h.264 can achieve the same quality as MPEG2 at around 1/4 the bitrate.

    I would recommend using CRF mode. For example, I know that CRF 18 at x264's Slow preset delivers pretty good quality with pretty much any video. Bitrate based encoding (ABR, 2-pass VBR, etc.) is really only useful when you need files of a particular size -- like when putting a lot of video on a CD/DVD. In cases like that you want to use the highest bitrate you can while still fitting on the disc.
    Last edited by jagabo; 28th Nov 2018 at 21:12.
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  4. Member
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    Originally Posted by jagabo View Post
    You can only decrease the qualitiy by re-encoding the existing MPEG2 files with h.264. If you go back the original sources you can get better quality at the same bitrate, the same quality at a much lower bitrate, or somewhere in between. If you recompress at the same bitrate the files will be the same size (aside from minor container overhead differences). Typically, h.264 can achieve the same quality as MPEG2 at around 1/4 the bitrate.

    I would recommend using CRF mode. For example, I know that CRF 18 at x264's Slow preset delivers pretty good quality with pretty much any video. Bitrate based encoding (ABR, 2-pass VBR, etc.) is really only useful when you need files of a particular size -- like when putting a lot of video on a CD/DVD. In cases like that you want to use the highest bitrate you can while still fitting on the disc.
    I am not re-encoding to try to get better quality. I do it to have all my movies in the AVC codec so they play well with subtitles on my Plex setups.
    But since I am doing it anyway, I was wondering if there is any advantage to change the original mode, which was CBR.

    You recommend CRF 18 - but what if the original video is not up to that quality? What will happen?
    And on the other hand, if the original quality is better than CRF 18, I would prefer to keep it that way. I have plenty of disk space.

    There is probably no answer to my questions, I will have to try.

    To the previous poster - I use Xmedia Recode for conversions
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  5. Member netmask56's Avatar
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    If you have plenty of disk space I would simply use MakeMKV, doesn't re-encode or change quality, basically size in = size out merely wraps the original in a MKV container. I've done this for my entire DVD and Blu ray collection. I have Plex on one of my setups and doesn't balk at any of my files. Basically I use a Popcorn A-500 media player connected via Ethernet to my NAS. If you haven't used MakeMKV it only takes a few minutes to process a DVD.
    BeyonWiz T3 PVR ~ Popcorn A-500 ~ Samsung ES8000 65" LED TV ~ Windows 7 64bit ~ Yamaha RX-A1070 ~ QnapTS851-4G
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  6. Originally Posted by aussie43 View Post
    I was wondering if there is any advantage to change the original mode, which was CBR.
    CBR is the least efficient encoding mode. ABR second worst. 2-pass VBR and CRF are about the same. The difference: with CRF you know the quality of the resulting video but not the size. With 2-pass VBR you know the size but not the quality.

    Originally Posted by aussie43 View Post
    You recommend CRF 18 - but what if the original video is not up to that quality? What will happen?
    The video won't be further degraded much (barely visible when comparing enlarged still frames).

    Originally Posted by aussie43 View Post
    And on the other hand, if the original quality is better than CRF 18
    MPEG2 at 17 Mbps? Not likely.
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  7. Member
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    MPEG2 at 17 Mbps? Not likely

    https://files.videohelp.com/u/286099/Screen%20Shot%2011-29-18%20at%2003.17%20PM.JPG

    Thanks, guys, I will try and see what happens if I select CRF 18
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  8. Member netmask56's Avatar
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    Code:
    Format                                   : MPEG-PS
    File size                                : 21.0 GiB
    Duration                                 : 2 h 18 min
    Overall bit rate mode                    : Constant
    Overall bit rate                         : 21.7 Mb/s
    
    Video
    ID                                       : 224 (0xE0)
    Format                                   : MPEG Video
    Format version                           : Version 2
    Format profile                           : Main@High
    Format settings                          : BVOP
    Format settings, BVOP                    : Yes
    Format settings, Matrix                  : Default
    Format settings, GOP                     : M=2, N=15
    Duration                                 : 2 h 18 min
    Bit rate mode                            : Constant
    Bit rate                                 : 20.8 Mb/s
    Maximum bit rate                         : 20.0 Mb/s
    Width                                    : 1 920 pixels
    Height                                   : 1 080 pixels
    Display aspect ratio                     : 16:9
    Frame rate                               : 24.000 FPS
    Color space                              : YUV
    Chroma subsampling                       : 4:2:0
    Bit depth                                : 8 bits
    Scan type                                : Progressive
    Compression mode                         : Lossy
    Bits/(Pixel*Frame)                       : 0.419
    Time code of first frame                 : 00:00:00:00
    Time code source                         : Group of pictures header
    GOP, Open/Closed                         : Open
    GOP, Open/Closed of first frame          : Closed
    Stream size                              : 20.1 GiB (96%)
    
    Audio
    ID                                       : 189 (0xBD)-128 (0x80)
    Format                                   : AC-3
    Format/Info                              : Audio Coding 3
    Commercial name                          : Dolby Digital
    Muxing mode                              : DVD-Video
    Duration                                 : 2 h 18 min
    Bit rate mode                            : Constant
    Bit rate                                 : 448 kb/s
    Channel(s)                               : 6 channels
    Channel layout                           : L R C LFE Ls Rs
    Sampling rate                            : 48.0 kHz
    Frame rate                               : 31.250 FPS (1536 SPF)
    Bit depth                                : 16 bits
    Compression mode                         : Lossy
    Stream size                              : 444 MiB (2%)
    Service kind                             : Complete Main
    BeyonWiz T3 PVR ~ Popcorn A-500 ~ Samsung ES8000 65" LED TV ~ Windows 7 64bit ~ Yamaha RX-A1070 ~ QnapTS851-4G
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  9. Member
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    OK, so I have the two files -

    "original" MPEG2 , CBR 17.2Mbps, size 12GB
    converted to H264 at CRF 18 size 4.6GB

    I was surprised that a pretty high quality setting will reduce the size so dramatically.

    The two files when played at normal speed look identical. But comparing them carefully side by side on VLC player, trying to find the same frame, the higher Mbps older MPEG2 codec seems to show some detail that I can't see on the H264 with much lower bitrate and size.
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    Originally Posted by jagabo View Post
    You can only decrease the qualitiy by re-encoding the existing MPEG2 files with h.264. If you go back the original sources you can get better quality at the same bitrate, the same quality at a much lower bitrate, or somewhere in between. If you recompress at the same bitrate the files will be the same size (aside from minor container overhead differences). Typically, h.264 can achieve the same quality as MPEG2 at around 1/4 the bitrate.
    mpeg2 is the original source, what do you think is on DVDs?
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  11. Originally Posted by surdelmavo View Post
    ou recommend CRF 18 - but what if the original video is not up to that quality? What will happen?
    Just like with a high quality source, you will get a video that's slightly lower quality than the source. Unless your source is very very low quality the resulting file will probably be smaller.

    Think of the CRF value as choosing how much quality to discard. At CRF=0 it is lossless -- you will lose no quality at all. But like with all lossless codecs you get a very large file. At CRF=12 it's difficult to see a difference between the source and the new file, even looking at enlarged still frames.

    Originally Posted by surdelmavo View Post
    And on the other hand, if the original quality is better than CRF 18, I would prefer to keep it that way.
    Any re-encoding with a lossy codec will reduce the quality. Even if you use a bitrate much higher than the source. The issue is how much quality you lose.

    Originally Posted by surdelmavo View Post
    I have plenty of disk space.
    Then why bother re-encoding?
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  12. Member
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    Originally Posted by jagabo View Post
    At CRF=12 it's difficult to see a difference between the source and the new file, even looking at enlarged still frames.
    Compare this statement with recommendations on other sites for using CRF 22 for blu rays. And my finding of some loss of detail at CRF 18.

    This is basically what I would like to see somewhere - a table showing relationship between CRF and bit rate.
    So if I have a rip, say, at CBR 20Mbps, and I need to re-encode, what CRF should I set to take advantage of the original high bit rate for the difficult frames, but save some storage space in the easy ones.
    I said that I don't have shortage of storage, but with a large number of files it eventually could be a factor, and maybe it could speed up the conversion process that takes hours.
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  13. Member
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    Some useful info here, look at the paragraph "How do quality and bitrate relate to each other"
    https://slhck.info/video/2017/02/24/crf-guide.html
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  14. Originally Posted by aussie43 View Post
    This is basically what I would like to see somewhere - a table showing relationship between CRF and bit rate.
    The correlation between the two is very low. The bitrate used in a CRF encode is entirely dependent on the complexity of the source. In crude terms, the more movement, the higher the bitrate needed for the same quality. Therefore, a 2-minute video of someone reading the news at CRF 18 will be a much smaller filesize than a different 2-minute video of a car chase also at CRF 18. Other variables should be the same (such as resolution, level, audio quality, etc.)

    So, you'll find no such table or graph.

    ...what CRF should I set to take advantage of the original high bit rate for the difficult frames, but save some storage space in the easy ones.
    Whatever CRF you choose already does that. That's what VBR (Variable BitRate) means - more bits for the complex scenes, fewer for the more static ones.
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  15. Originally Posted by aussie43 View Post
    This is basically what I would like to see somewhere - a table showing relationship between CRF and bit rate.
    There's no such thing. Different videos require different bitrates to retain quality. You could make such a table for one video but it may be meaningless for the next. For example, anime usually compress much more easily than a grainy live action film like The 300. Using CRF mode will automatically adapt to the content. So just encode a few test videos at different CRF values to find what you can live with. Then encode all your videos at (or near) that setting.

    I usually encode DVD rips around CRF 18, but Blu-ray rips around 20. The idea here is that the small defects will be made more visible when the small DVD frame is upscaled to full screen for viewing.
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