How can I play video while showing all informations in the file? - Page 1
Forum section: electronics / general

author: Logan
author_rank: Frequent Contributor
timestamp: June 26, 2022, 11:58:11 am
content: Hi friends.This is a strange problem I found recently. You can also test it:Block your camera lens, and set exposure to lowest. Record a video for several seconds.Play it on VLC, make a screenshot, then use some tool (such as fotoxx) to inspect the picture, all pixels would be #000000.On VLC menu > tools > effects and filters > video effects, turn up gamma until you will actually see something, like random hot pixels.Test on some other video players, all pixels are still #000000.So here you see the problem, most(if not all) video players do not show all available information in original file. Why? And How can I force it to show?I tried the tone mapping setting in VLC, which is the most relevant I think, but there's no improvement.Welcome to discuss. Thanks.

author: mariush
author_rank: Super Contributor
timestamp: June 26, 2022, 12:27:35 pm
content: You assume the video file actually had more information that other players don't show it.You're wrong.It makes more sense to put the blame on VLC. It may use some algorithms to adjust brightness or gamma that have some rounding errors or those algorithms may have some optimizations (for speed purposes) that cause artefacts in some rare cases or edge cases, but 99.999% of the time work perfectly well.Think of it like Quake's inverse square root -https://en.wikipedia.org/wiki/Fast_inverse_square_root- which produces a "eh, good enough" result in much much shorter time compared to regular calculations - an algorithm could use such approximations that produce that "eh, good enough" conversion to another gamma or brightness , but once in a while produce some artefacts.Oh ... and don't rule out the video codecs used to compress the video as I assume you don't use raw footage. Codecs work with blocks of 8x8 to 64x64 blocks of pixels, and compress the contents, and there's key frames, predicted frames etc etcIn addition to that, modern video codecs don't use RGB when compressing, they convert the image to YV12 (luminance and Chrominances YCbCr - in YV12 the luminance is stored fully, but Cb and Cr are stored as average of the value of 4 pixels at a time)It's possible for some bug in VLC to occur in the pipeline decode video to raw yv12 -> apply gamma/brightness --> convert yv12 to RGB --> copy to video card memory buffer and render on screen.

author: Logan
author_rank: Frequent Contributor
timestamp: June 26, 2022, 03:07:48 pm
content: Quote from: mariush on June 26, 2022, 12:27:35 pmThank you for your thoughts!But sorry I cannot agree with the quoted part.The "revealed" image are not the same with each video, and sometimes I can even see the "lens correction" pattern done by the camera.

author: DiTBho
author_rank: Super Contributor
timestamp: June 27, 2022, 02:27:20 pm
content: I had the same problem hacking a HDMI to Ethernet, the receiver needed a fine tuning so I had to use a video player to correct its setting on the fly.At the end, I gave up with VLC and used mplayer.It's not smart as VLC but it's easier to be hacked