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  1. I often record “catch-up” broadcasts from french TV channel Arte, and recently, when comparing videos of programs which have already been broadcast a year or two ago, and which I already recorded at the time (either because I forgot that I already had them, or to check if the encoding quality had improved in the mean time), I noticed a dictinct color discrepancy. I know that this is generally due to the use of a correct or incorrect YUV-RGB color conversion matrix. It would seem like they now do the encoding with the wrong matrix. But before I try to report the issue (which is going to be tricky, both because there doesn't seem to be an easily accessible “contact” area anymore, and because those videos are not supposed to be downloaded...), could someone confirm that the colors appear to be wrong on the most recent videos, and not the other way around ? There seems to be a general blue/purple tint on the most recent videos, and the skin tones seem off, am I right ? Is there a likely explanation to this, considering that the encoding parameters haven't changed as far as I can see ? According to MediaInfo : same AVC profile, approximately same bitrate... But strangely the newer videos report a “BT.709” color conversion matrix, which should be correct, while the older ones didn't display that field – although it seems to vary, some recent videos don't have that field either. Is this relevant at all ?


    “Zétwal”, documentary broadcast on 2019-07-16 (screenshot 1) and 2020-07-21 (screenshot 2)
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    “Zapped”, documentary about Frank Zappa broadcast on 2017-03-17 (screenshot 1) and 2020-07-25 (screenshot 2)
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    (This one would have been an improvement if not for that issue, as the vertical logo is less disturbing over 4:3 archive footage which form the bulk of this documentary – which is excellent by the way.)

    “Toni Erdmann”, movie broadcast on 2018-11-12 (screenshot 1) and 2020-07-29 (screenshot 2)
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    MediaInfo report for “Zapped” 2017-03-17 :
    Code:
    Général
    Nom complet                              : F:\A CLASSER 2\Arte\2017\201703172223 - Arte - Zapped - Frank Zappa par Frank Zappa {vu 20170325 +++}.mp4
    Format                                   : MPEG-4
    Profil du format                         : Base Media / Version 2
    Identifiant du codec                     : mp42 (isom/mp42)
    Taille du fichier                        : 1,02 Gio
    Durée                                    : 1 h 0 min
    Type de débit global                     : Variable
    Débit global moyen                       : 2 420 kb/s
    Date d'encodage                          : UTC 2017-03-15 22:40:56
    Date de marquage                         : UTC 2017-03-15 22:40:56
    
    Vidéo
    ID                                       : 1
    Format                                   : AVC
    Format/Info                              : Advanced Video Codec
    Profil du format                         : Main@L3.1
    Paramètres du format                     : CABAC / 3 Ref Frames
    Paramètres du format, CABAC              : Oui
    Paramètres du format, RefFrames          : 3 images
    Identifiant du codec                     : avc1
    Identifiant du codec/Info                : Advanced Video Coding
    Durée                                    : 1 h 0 min
    Débit                                    : 2 290 kb/s
    Largeur                                  : 1 280 pixels
    Hauteur                                  : 720 pixels
    Format à l'écran                         : 16/9
    Type d'images/s                          : Constant
    Images par seconde                       : 25,000 Im/s
    Norme                                    : PAL
    Espace de couleurs                       : YUV
    Sous-échantillonnage de la chrominance   : 4:2:0
    Profondeur des couleurs                  : 8 bits
    Type de balayage                         : Progressif
    Bits/(Pixel*Image)                       : 0.099
    Taille du flux                           : 991 Mio (95%)
    Date d'encodage                          : UTC 2017-03-15 22:40:57
    Date de marquage                         : UTC 2017-03-15 22:40:57
    Gamme de couleurs                        : Limited
    Codec configuration box                  : avcC
    
    Audio
    ID                                       : 2
    Format                                   : AAC LC
    Format/Info                              : Advanced Audio Codec Low Complexity
    Identifiant du codec                     : mp4a-40-2
    Durée                                    : 1 h 0 min
    Type de débit                            : Variable
    Débit                                    : 125 kb/s
    Débit maximum                            : 168 kb/s
    Canaux                                   : 2 canaux
    ChannelLayout                            : L R
    Echantillonnage                          : 48,0 kHz
    Images par seconde                       : 46,875 Im/s (1024 SPF)
    Mode de compression                      : Avec perte
    Taille du flux                           : 54,3 Mio (5%)
    Date d'encodage                          : UTC 2017-03-15 22:40:57
    Date de marquage                         : UTC 2017-03-15 22:40:57
    MediaInfo report for “Zapped” 2020-07-25 :
    Code:
    Général
    Nom complet                              : M:\2020_07_2500_46 - Arte - Zapped - Frank Zappa par Frank Zappa.mp4
    Format                                   : MPEG-4
    Profil du format                         : Base Media / Version 2
    Identifiant du codec                     : mp42 (isom/mp42)
    Taille du fichier                        : 1 000 Mio
    Durée                                    : 1 h 0 min
    Type de débit global                     : Variable
    Débit global moyen                       : 2 311 kb/s
    Date d'encodage                          : UTC 2020-07-21 11:38:13
    Date de marquage                         : UTC 2020-07-21 11:38:13
    
    Vidéo
    ID                                       : 1
    Format                                   : AVC
    Format/Info                              : Advanced Video Codec
    Profil du format                         : Main@L3.1
    Paramètres du format                     : CABAC / 3 Ref Frames
    Paramètres du format, CABAC              : Oui
    Paramètres du format, RefFrames          : 3 images
    Identifiant du codec                     : avc1
    Identifiant du codec/Info                : Advanced Video Coding
    Durée                                    : 1 h 0 min
    Type de débit                            : Variable
    Débit                                    : 2 200 kb/s
    Largeur                                  : 1 280 pixels
    Hauteur                                  : 720 pixels
    Format à l'écran                         : 16/9
    Type d'images/s                          : Constant
    Images par seconde                       : 25,000 Im/s
    Norme                                    : PAL
    Espace de couleurs                       : YUV
    Sous-échantillonnage de la chrominance   : 4:2:0
    Profondeur des couleurs                  : 8 bits
    Type de balayage                         : Progressif
    Bits/(Pixel*Image)                       : 0.095
    Taille du flux                           : 944 Mio (94%)
    Date d'encodage                          : UTC 2020-07-21 11:38:15
    Date de marquage                         : UTC 2020-07-21 11:38:15
    Gamme de couleurs                        : Limited
    Coordonnées de chromaticité              : BT.709
    Caractéristiques du transfert            : BT.709
    Coefficients de la matrice               : BT.709
    Codec configuration box                  : avcC
    
    Audio
    ID                                       : 2
    Format                                   : AAC LC
    Format/Info                              : Advanced Audio Codec Low Complexity
    Identifiant du codec                     : mp4a-40-2
    Durée                                    : 1 h 0 min
    Type de débit                            : Variable
    Débit                                    : 125 kb/s
    Débit maximum                            : 170 kb/s
    Canaux                                   : 2 canaux
    ChannelLayout                            : L R
    Echantillonnage                          : 48,0 kHz
    Images par seconde                       : 46,875 Im/s (1024 SPF)
    Mode de compression                      : Avec perte
    Taille du flux                           : 54,3 Mio (5%)
    Date d'encodage                          : UTC 2020-07-21 11:38:15
    Date de marquage                         : UTC 2020-07-21 11:38:15
    Last edited by abolibibelot; 4th Aug 2020 at 23:29.
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  2. Member
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    I've seen this affect on my LG TV; the TV comes with xumo.tv built-in, a thing they call "channel plus".
    It's an adaptive stream over the internet. Quite often, when a channel is first selected, the picture
    is fuzzy (low resolution) and the color leans towards the magenta side.
    After a few seconds, the higher res picture comes in, and the color also corrects.

    I had always assumed the TV was using rec609 for a few seconds when the feed is low-res SD.
    then switches to rec709 when in locks in at 720p or better.

    Do you see this issue on the TV and PC? Perhaps the files are incorrectly encoded.
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  3. All screenshots have been made with VLC Media Player on the same system. The discrepancy seems constant throughout each set of videos of the same program. TV / PC seems irrelevant here (anyway I don't have a TV, watch everything on the computer screen). The videos were downloaded as standalone MP4 files from basic HTTP URLs (with a dedicated software called Captvty), not some sort of adaptive streams.

    Two of those are still available (the 2020 versions of course) :
    https://www.arte.tv/fr/videos/086911-000-A/zetwal/ origin HTML page which leads to JSON page with video URLs :
    https://api.arte.tv/api/player/v1/config/fr/086911-000-A which leads to direct link in 1280x720 :
    https://arteptweb-a.akamaihd.net/am/ptweb/086000/086900/086911-000-A_SQ_0_VOF-STF_0510...1MysEm7aG8.mp4
    https://www.arte.tv/fr/videos/048387-000-A/zapped-frank-zappa-par-frank-zappa/
    https://api.arte.tv/api/player/v1/config/fr/048387-000-A
    https://arteptweb-a.akamaihd.net/am/ptweb/048000/048300/048387-000-A_SQ_0_VO-STF_05128...1NGWUmreOk.mp4

    Perhaps the files are incorrectly encoded.
    That's what I asked : based on those screenshots, which of them are most likely incorrectly encoded ? The ones from 2017-2019 or the ones from 2020 ?
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  4. Well ? é_è
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    Originally Posted by abolibibelot View Post
    Well ? é_è
    Well what? I already inferred that the earlier images look more accurate (to me)
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  6. Well what? I already inferred that the earlier images look more accurate (to me)
    Well, no (or it was very subtly inferred), but now you have.

    I expected some sort of technical insight ; for instance the second set of screenshots shows a color chart, which must be used for the very purpose of checking if the colors are about accurate, so, shouldn't an experienced video technician, seeing the color chart on the second screenshot, immediately realize that something is wrong, with that glowing green strip in the middle ?
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    Originally Posted by abolibibelot View Post
    Well what? I already inferred that the earlier images look more accurate (to me)
    Well, no (or it was very subtly inferred), but now you have.

    I expected some sort of technical insight ; for instance the second set of screenshots shows a color chart, which must be used for the very purpose of checking if the colors are about accurate, so, shouldn't an experienced video technician, seeing the color chart on the second screenshot, immediately realize that something is wrong, with that glowing green strip in the middle ?
    Perhaps somebody else will provide some more specific info. I downloaded the Zappa file,
    the video levels are within the normal (limited) range.
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  8. One problem is VLC. Always double check with other tools than VLC, which is known to have various issues

    This is what it should look like for "048387-000-A_SQ_0_VO-STF_05128682_MP4-2200_AMM-PTWEB_1NGWUmreOk.mp4" for 709

    You can check with another player, or explictly control the RGB conversion
    Image
    [Attachment 54389 - Click to enlarge]


    But it's still "off". Black is correct, but white is neither 75% or 100% . Usually PAL EBU bars have white at 100%. Maybe they are supposed to be something else, but everything except black is off.

    I can't comment on the older videos, because you took those screenshots with VLC too...
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  9. Yes I remember being told, most likely by you, about VLCMP's unreliability with regards to screenshots, and color rendering in general, but in this case, since the screenshots were made from individual downloaded files which are otherwise similar, the discrepancy has to come from somewhere within the files themselves.

    Anyway, screenshots taken with AVSPMod (supposedly reliable) show the same pattern :

    Click image for larger version

Name:	Zapped 20170317 F100.png
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    screenshot from 20170317 file

    Click image for larger version

Name:	Zapped 20200725 F100.png
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    screenshot from 20200725 file

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    20170317 + 20200725 StackVertical

    Note : This is not the exact same frame as in the first post. In fact in the first post the two screenshots don't show the exact same frame, as I took them right at the beginning of the first subtitle, but I noticed that the first subtitle appears 2 frames earlier on the 2020 video. Here both are frame 100 and the actual footage begins at frame 122.

    Another set (frame 16315) :

    Click image for larger version

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    screenshot from 20170317 file

    Click image for larger version

Name:	Zapped 20200725 F16315.png
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    screenshot from 20200725 file
    Last edited by abolibibelot; 5th Aug 2020 at 18:47.
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  10. You can examine it using color picker. e.g. avspmod has one

    75% bars , when using full range RGB (computer RGB 0-255) should be 191 in the appropriate channel . For example "75% red" would be RGB 191,0,0 . "75% yellow" would be RGB 191,191,0 . It's normal to have slightly off +/-3 , rounding errors. Yes there is a discrepancy between each other, and both are "off" significantly if you assume those are supposed to be 75% color bars. You have to assume "white" is 75% white (it should be 191,191,191) . But EBU bars typically use 100% white
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  11. You can examine it using color picker. e.g. avspmod has one
    Where ? Is it the “hex” value at the bottom ?

    75% bars , when using full range RGB (computer RGB 0-255) should be 191 in the appropriate channel . For example "75% red" would be RGB 191,0,0 . "75% yellow" would be RGB 191,191,0 . It's normal to have slightly off +/-3 , rounding errors. Yes there is a discrepancy between each other, and both are "off" significantly if you assume those are supposed to be 75% color bars. You have to assume "white" is 75% white (it should be 191,191,191) . But EBU bars typically use 100% white
    Well, I don't know much about those broadcasting standards, but this is old archive footage edited into a documentary meant to be broadcast on current television devices, perhaps it was deemed too bright and was darkened somewhat to keep the global levels about consistent throughout the movie. What matters is the relative levels of colors and how accurately the video preserves the tones or the original material (in this case that means the “master” video file of that documentary used for the broadcast, which I would suppose is the same that was used in 2017). It seems to me that the colors are more “balanced”, for lack of a better word, on the 2017 version, and the skin tones seem more natural. Is this verified by the measurements ?
    Also, what about the newer standards, Rec. 2020 / Rec. 2100 ? How are the colors affected when footage encoded with Rec. 709 is mistakenly rendered with Rec. 2020 for instance ? (Those settings are not available in AVSPMod as far as I can see. Are they available in current versions of Avisynth, natively or through a plugin ?) Would it be possible that the broadcaster now uses those standards geared toward “4K” broadcast ? (Assuming that this makes sense, of which I'm not so sure right now.)
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  12. Originally Posted by abolibibelot View Post
    You can examine it using color picker. e.g. avspmod has one
    Where ? Is it the “hex” value at the bottom ?

    If you don't see it - you might not have it enabled for RGB

    options=> program settings => video => customize video status bar => add %RGB after %HEX . You can add %YUV too. In the status bar, when there is an * asterisk, it means converted value. So if input was RGB, RGB would not have an asterisk, but YUV and HEX would have an asterisk


    Well, I don't know much about those broadcasting standards, but this is old archive footage edited into a documentary meant to be broadcast on current television devices, perhaps it was deemed too bright and was darkened somewhat to keep the global levels about consistent throughout the movie. What matters is the relative levels of colors and how accurately the video preserves the tones or the original material (in this case that means the “master” video file of that documentary used for the broadcast, which I would suppose is the same that was used in 2017). It seems to me that the colors are more “balanced”, for lack of a better word, on the 2017 version, and the skin tones seem more natural. Is this verified by the measurements ?
    I don't have the old version to look at. "balanced" can be subjective ; and the lighting is not neutral in all shots; and the color and grading is inconsistent across different shots (rightly so, it's composed from different sources, cameras, times)

    Also, what about the newer standards, Rec. 2020 / Rec. 2100 ? How are the colors affected when footage encoded with Rec. 709 is mistakenly rendered with Rec. 2020 for instance ? (Those settings are not available in AVSPMod as far as I can see. Are they available in current versions of Avisynth, natively or through a plugin ?) Would it be possible that the broadcaster now uses those standards geared toward “4K” broadcast ? (Assuming that this makes sense, of which I'm not so sure right now.)
    You can convert using 2020 if you wanted to check. Or other matrices, or any combination. Those are available to you in avisynth / vapoursynth/ ffmpeg etc...

    e.g.
    ConvertToRGB24(matrix="Rec2020")

    Note many broadcasters still use 709 for UHD. And the assumption that the attached colorbars are valid or representative of the program is not necessarily true. Maybe they were attached at some 3rd or 4th generation stage, but different than the original program. There are dozens of places in the workflow where something could have gone wrong . Some guy pushes a button and you get a different color 3 years later.
    Last edited by poisondeathray; 5th Aug 2020 at 21:23.
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  13. options=> program settings => video => customize video status bar => add %RGB after %HEX . You can add %YUV too. In the status bar, when there is an * asterisk, it means converted value. So if input was RGB, RGB would not have an asterisk, but YUV and HEX would have an asterisk
    Alright, works. And so what is “hex” ?

    I don't have the old version to look at.
    I uploaded a 10s segment cut with ffmpeg -c copy -t 10.

    "balanced" can be subjective ; and the lighting is not neutral in all shots; and the color and grading is inconsistent across different shots (rightly so, it's composed from different sources, cameras, times)
    I mean, on those screenshots I provided. The green seems too bright and the red too dark, which from my admittedly limited experience indicates that a conversion was made with the wrong matrix.

    ConvertToRGB24(matrix="Rec2020")
    Works indeed – I didn't try it before since it wasn't among the options listed by AVSPM, so I assumed that it wasn't available the currently installed version of Avisynth.
    If I convert the 2017 version with "Rec2020" it doesn't produce a similar aspect to the 2020 version (the green is slightly lighter but not as much).
    But if I convert the 2017 version with "Rec601" the aspect is very close to the 2020 version converted with "Rec709" (frame 100 again).
    Click image for larger version

Name:	Zapped 20170317 RGB Rec601 + 20200725 RGB Rec709 StackV F100.png
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    Note many broadcasters still use 709 for UHD. And the assumption that the attached colorbars are valid or representative of the program is not necessarily true. Maybe they were attached at some 3rd or 4th generation stage, but different than the original program. There are dozens of places in the workflow where something could have gone wrong . Some guy pushes a button and you get a different color 3 years later.
    Again, what I noticed is a general pattern, seemingly affecting all videos from that provider recently. And the main question was : was it correct before and is it incorrect now, or was it incorrect before and is it correct now ? The first hypothesis seems more likely, but I'd like to be sure before I report it.
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  14. Originally Posted by abolibibelot View Post
    And so what is “hex” ?
    Hexidecimal value describing a "color" . A "color" can be expressed as HSL too

    e.g
    https://htmlcolorcodes.com/


    I mean, on those screenshots I provided. The green seems too bright and the red too dark, which from my admittedly limited experience indicates that a conversion was made with the wrong matrix.
    Yes, but both have issues.

    This is not as simple as a single matrix conversion error. Maybe primaries were adjusted (e.g. PAL has different slightly primaries than NTSC, but primaries are usually ignored), maybe matrix conversion a few times (other than 709/601) . There are other parameters that can be adjusted (other than matrix), and there are other matrices than 601/709/2020

    But if I convert the 2017 version with "Rec601" the aspect is very close to the 2020 version converted with "Rec709" (frame 100 again)
    Likely that's what happened.


    And the main question was : was it correct before and is it incorrect now, or was it incorrect before and is it correct now ? The first hypothesis seems more likely, but I'd like to be sure before I report it.
    If you assume the bars are correct, then neither is "correct" . But I'd say it's probably less correct now
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  15. This is not as simple as a single matrix conversion error.
    Likely that's what happened.
    This seems a bit contradictory...

    Maybe primaries were adjusted (e.g. PAL has different slightly primaries than NTSC, but primaries are usually ignored)
    What are primaries, in a nutshell ?

    There are other parameters that can be adjusted (other than matrix), and there are other matrices than 601/709/2020
    What would be the other commonly used matrices for standard YUV broadcasting ?
    Of course many things can be adjusted in video, but this shift to lighter greens and darker reds is quite characteristic.

    Would it be possible to tweak the levels in such a way that the bars appear perfectly standard, to see how it would affect the rest of the footage ?
    And is it possible to display a video converted with a wrong color conversion matrix so as to obtain the same aspect it would have if it had been converted with the correct matrix, or has some part of the color information been lost in the process ?
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  16. Originally Posted by abolibibelot View Post
    This is not as simple as a single matrix conversion error.
    Likely that's what happened.
    This seems a bit contradictory...

    2017 version was wrong to begin with (if you trust the bars). 2020 version is 2017 version + ~Rec601 shift on top (so it's "more" wrong) . That's what your observation suggested and I agree :
    But if I convert the 2017 version with "Rec601" the aspect is very close to the 2020 version converted with "Rec709" (frame 100 again)

    What are primaries, in a nutshell ?

    They describe the x,y coordinates of the "primary" colors (red, blue, green) . 709, "NTSC" and "PAL" have different values. (But in practice, the primaries are usually not adjusted for when conversion between different formats, but maybe that's contributing to why 2017 is "wrong" too)



    What would be the other commonly used matrices for standard YUV broadcasting ?
    Those are it.

    But it's people (some doofus) that make mistakes. This is common. Some guy runs the video though some software, but it uses different parameters. E.g. Many types of mac software use slightly different gamma /transfer characteristics.


    Of course many things can be adjusted in video, but this shift to lighter greens and darker reds is quite characteristic.
    Yes, for the 2017 version to 2020 version difference

    But I'm looking at the colorbars - they should be "known" reference colors. That's what they are there for. If it was a simiple 709/601 mistmatch then specifying the correct matrix or using colormatrix and reversing the transform should get you the correct results. ie. You should be able to fix 2017 to whatever earlier original "correct" result was

    Would it be possible to tweak the levels in such a way that the bars appear perfectly standard, to see how it would affect the rest of the footage ?
    And is it possible to display a video converted with a wrong color conversion matrix so as to obtain the same aspect it would have if it had been converted with the correct matrix, or has some part of the color information been lost in the process ?
    That's what the bars are for - if you assume they were correct and there since the beginning. Yes, it should possible , with color mixer or masks

    If it was a simple 601/709 shift, you should be able to easily "fix" 2017, but that's not the case . That suggests a bunch of other things were done to get that 2017 result. You can easily "fix" 2020 to get 2017 or "reverse" what had been done (e.g. colormatrix(mode="rec.709->rec.601",clamp=0) ) . But 2017 is still "wrong" according to the bars, and there is no easy 1 line fix to get the original bars
    Last edited by poisondeathray; 6th Aug 2020 at 16:42.
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