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  1. so I have dual screen, total of two potplayer instances active, calling it A.mp4 and B.mp4 two videos, one on each screen.

    how can I get both these videos to play at the same time, to view differences between video A/B etc.

    I have tried to set "play" (space bar in my case the default key) as global key and was hoping if i press spacebar/play it'll send the command to play both video at sametime but it only plays 1 video and its random.

    please help! or suggest any video player that can do this
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  2. I don't know of a player that'll do it. The same thing happens with MPC-HC. What I did is change the fullscreen mouse option to "middle down" because a double click for that seems mental anyway, then I set "left down" for Play/Pause. The result is you can left click on the video quickly in order to pause and play, without any chance of the player jumping in and out of full screen mode.

    It's not an ideal solution, but you can start one playing, start the second, then click on the first one to pause it and start playback again, and repeat the process until the second one has caught up.

    Another option might be to open each video with Avisynth, stack them horizontally, and stretch the player window to cover both monitors. You should be able to position it so you have a video on each monitor, and as there's only a single player, they'll always be in sync. Assuming you're an Avisynth user....

    A = FFMS2("SomeVideo.mkv")
    B = FFMS2("AnotherVideo.mkv")
    StackHorizontal(A, B)
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  3. I do A/B comparisons all the time in my NLE (Vegas Pro). However, I have never tried to place the two videos onto two different monitors. However, if the main goal is to simply look at two versions of the same video in order to spot differences, that is how I would recommend doing it. The advantage of an NLE is you have total control over the play head and can easily move backwards and forwards through the video; you can set markers to which you can quickly return; you can label each spot that requires attention; and if needed, you can make corrections to one of the videos right there in the editor.
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  4. Originally Posted by johnmeyer View Post
    I do A/B comparisons all the time in my NLE (Vegas Pro). However, I have never tried to place the two videos onto two different monitors. However, if the main goal is to simply look at two versions of the same video in order to spot differences, that is how I would recommend doing it. The advantage of an NLE is you have total control over the play head and can easily move backwards and forwards through the video; you can set markers to which you can quickly return; you can label each spot that requires attention; and if needed, you can make corrections to one of the videos right there in the editor.
    using video editing software with 2 video tracks and compare them is a nice idea, only problem I see with this, is that videos are extremely small.

    is it possible to stretch video to take up most of the screen have the two mp4/mkv side by side? with NLE vegas pro i mean.
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  5. Originally Posted by hello_hello View Post
    I don't know of a player that'll do it. The same thing happens with MPC-HC. What I did is change the fullscreen mouse option to "middle down" because a double click for that seems mental anyway, then I set "left down" for Play/Pause. The result is you can left click on the video quickly in order to pause and play, without any chance of the player jumping in and out of full screen mode.

    It's not an ideal solution, but you can start one playing, start the second, then click on the first one to pause it and start playback again, and repeat the process until the second one has caught up.

    Another option might be to open each video with Avisynth, stack them horizontally, and stretch the player window to cover both monitors. You should be able to position it so you have a video on each monitor, and as there's only a single player, they'll always be in sync. Assuming you're an Avisynth user....

    A = FFMS2("SomeVideo.mkv")
    B = FFMS2("AnotherVideo.mkv")
    StackHorizontal(A, B)
    so avisynth does not allow multiple instances but can open multiple video in 1 window?
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  6. About that NLE, as johnmeyer recommended, yes, we all get caried away to do everything in avisynth or vapoursynth now, but if you have Magic Vegas:
    - put videos underneath each other into tracks , set full screen view (with best, full preview) and just toggle pressing 'X' on keyboard, this wold make each track a 'solo', so you switch frames basically. If your NLE is something good, it might have this sort of 'tools'.

    This has the same effect as interleave it in Avisynth or Vapoursynth. Comparing videos next to each other does not work if looking for details, because light and angles, neighboring colors play tricks on you. You have to change frame and looking in the same spot, having video with frames, A1,B1,A2,B2, and when advancing one step back or forth a subtle changes just jump at you.
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  7. Originally Posted by wtfiwinomgs View Post
    so avisynth does not allow multiple instances but can open multiple video in 1 window?
    AviSynth allows any number of instances, just use two scripts and two players/editors. Two scripts:

    Code:
    FFMS2("SomeVideo.mkv")
    Code:
    FFMS2("AnotherVideo.mkv")
    Open them in two players. But there's no automatic syncronization between the players. It's basically the same as just opening the two videos directly in two players.

    Viewing two videos side by side is good for seeing motion artifacts. But if you really want to see even the minutest differences between two videos you want to interleave them frame by frame:

    Code:
    A = FFMS2("SomeVideo.mkv")
    B = FFMS2("AnotherVideo.mkv")
    Interleave(A, B)
    You can then swap back and forth between the same frame in the two videos using the forward/backward controls in an editor -- like VirtualDub with the left and right arrow keys. Combine that with a screen Magnifier (Windows built in magnifier is good for this) and you'll be able to see the tiny of differences. When I'm comparing two encodings I interleave three videos, the source, one encoding, and the other encoding. I like to do it this way:

    Code:
    source = "LWlibavVideoSource("source.mkv")
    enc1 = "LWlibavVideoSource("encoding1.mkv")
    enc2 = "LWlibavVideoSource("encoding2.mkv")
    Interleave(source, enc1, enc2, source)
    This lets you swap back and forth directly between the source and enc1, enc1 and enc2, and enc2 and the source. I used LWlibavVideoSource in that example because I usually prefer it over FFMS2.
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  8. I agree that AVISynth is totally the wrong tool for this job.

    I too use Vegas (I have the Pro version, but the simple version will work as well). The size of the video doesn't matter at all. I have edited videos as tiny as 160x120 pixels such as this one: Horses. That sample is from a 1991 first-generation digital video. You can enlarge and zoom into the video as much as you want to, and do it very simply, using a GUI interface rather than trying to do everything through code.

    So, to reiterate, I love AVISynth, but would never ever consider it for this task.

    P.S. Here's a link to a portion of the original 160x120 12 fps video before I performed restoration:

    https://www.mediafire.com/file/y76a852bflv2737/clip.avi/file

    That is what digital video looked like folks, when we first started out on this digital adventure, eventually leaving the analog domain behind.
    Last edited by johnmeyer; 29th Jun 2020 at 19:30. Reason: typos
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  9. P.S. Here are two similar videos, set up to play side-by-side in Vegas:

    https://forum.videohelp.com/attachment.php?attachmentid=54005&stc=1&d=1593478184
    Image Attached Thumbnails Click image for larger version

Name:	Drone side-by-side.png
Views:	15
Size:	982.8 KB
ID:	54005  

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  10. Originally Posted by johnmeyer View Post
    P.S. Here are two similar videos, set up to play side-by-side in Vegas:

    https://forum.videohelp.com/attachment.php?attachmentid=54005&stc=1&d=1593478184
    in your attached screenshot. that "video preview" window, can it go full screen?

    also I see its comparing two videos side by side but seems the two video are somewhat cropped on the horizontal length, meaning you can compare two videos but only see a portion of the two videos.

    most of my 2 videos most narrow will still be 640 x 480 so 4:3 and two of them side by side will become 4 by 6, i dont wish to have them each cropped and become a regular widescreen and lose some outer part of the videos.
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  11. Originally Posted by wtfiwinomgs View Post
    Originally Posted by johnmeyer View Post
    P.S. Here are two similar videos, set up to play side-by-side in Vegas:

    https://forum.videohelp.com/attachment.php?attachmentid=54005&stc=1&d=1593478184
    in your attached screenshot. that "video preview" window, can it go full screen?

    also I see its comparing two videos side by side but seems the two video are somewhat cropped on the horizontal length, meaning you can compare two videos but only see a portion of the two videos.

    most of my 2 videos most narrow will still be 640 x 480 so 4:3 and two of them side by side will become 4 by 6, i dont wish to have them each cropped and become a regular widescreen and lose some outer part of the videos.
    I spent 30 seconds doing this. A little more time and I could get closer to what you want.

    What exactly are you trying to do? If the goal is to see the differences, which is what you said in your initial post, this will work just fine, even if the video cannot be precisely full screen. You can easily get it to 90% of full screen, and you can get the videos to play side-by-side.

    However, there is no way you can play two HD videos side-by-side on a normal screen without cropping. This is a "square peg in round hole" problem, because any normal computer or TV display is designed to fit one HD video and when you put two side-by-side, basic geometry dictates that you will have to have black bars at top and bottom.

    If you absolutely insist on full screen, Vegas can easily squish the videos so they will conform to a 16:9 space, but they'll look like garbage and I think you'll have a tough time seeing the differences.
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