WhatIs: Backdoor

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If there is a method for a computer to receive commands from someone else instead of the user, that method is called a backdoor. Backdoors that allow full control over the operating system are said to be "universal".

There can be backdoors in hardware or software.

Sometimes, backdoors that are designed for "legitimate" uses are exploited illegitimately.

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Intel 7th and 8th generation processor graphics driver for Windows 7/8/8.1

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AV1 vs VP9 vs AVC (h.264) vs HEVC (h.265): Part II - Fidelity

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In this part, we tested the lossy compression capability. "Lossy" means that in order to reduce data size, the data is inexactly approximated and part of it is discarded. To measure the fidelity of the reconstruction (encoded video) of lossy compression codecs in our tests, we used PSNR (Peak signal-to-noise ratio).The greater the PSNR of two videos, the more similar they are. If the encoded video is lossless, the PSNR will be infinity when compared to the original.We tried to match the PSNR and compared the video stream size, the smaller the size, the better the codec. But it is hard to make the PSNR exactly the same. As mentioned earlier, as of June 2018, the AV1 is still experimental and we were not able to set its constant quality mode as we expected. And AV1 is extremely slow. So we did the AV1 in its vibrate bitrate mode first. We have found that the VP9 produces better results when encoded in its 2-pass constant quality mode (can be set with "-crf"), so we c…
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AV1 vs VP9 vs AVC (h.264) vs HEVC (h.265): Part IV - Decode

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In this part, we tested the decoding speed. Especially for video coding formats designed for video transmissions over the Internet, decoding speed could be much more important than encoding speed. We tried to encode in 2-pass vibrate bitrate mode (VBR) to get almost the same file sizes and counted the time needed for converting the encoded videos into raw video files. we decoded in RAM, because decoding is fast and the raw video could be very large. We also encoded in RAM this time, but the improvement of encoding speed, if any, wasn't very impressive.ConclusionAt of June 2018, the AV1 decoder can only decode in a single thread. Decoders for H.264, H265, and VP9 utilize multi-threads.We were not able to play videos encoded with AV1 in Chrome, Firefox Nightly, VLC, both on Windows and LINUX, though those are claimed to be able to.To decode the files encoded with AV1, the CPU time was approximately 3.5-6x longer than that to decode files encoded with x264. This means that it require…
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AV1 vs VP9 vs AVC (h.264) vs HEVC (h.265): Part I - Lossless

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ConclusionIn terms of lossless compression, x264 and x265 took less time and produced smaller files. All video codecs produced smaller video files than LZMA/LZMA2, the general purpose compression algorithms.In our tests, AV1 takes approximately 160-190x more time than x264 to encode in their lossless mode. AV1 does have a lossless mode, but the output is not lossless at all.VP9 and AV1 can take advantage of multi-threading, but they can not load all CPU cores all the time as x264 and x265 do.NoteAt of June 2018, AV1 is still experimental.We used x264 as the AVC encoder.We used x265 as the HEVC encoder.We used pxz as the LZMA/LZMA2 compressor. LZMA is also the default algorithm of 7-Zip.The AV1 encoder ran with "--cpu-used=4" for "medium" speed, "--tile-columns=4" to enabling multi-threading. All encoders ran in their lossless mode, all other settings were as default.Test 1Source video
sintel_trailer_2k_480p24.y4m
© copyright Blender Foundation | durian.bl…
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OBS Studio settings for best quality (loseless) recording

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OBS - Open Broadcaster Software. Change Color Format to RGB. RGB is the color format in which computer hardwares talk, thus loseless. The lose in transformating to YUV is noticeable, especially for color gradients. H.264 video in RGB color format can be played by VLC and other FFmpeg-based players. Choose FFmpeg and select matroska as the container, libx264rgb as the video encoder, flac as the audio encoder.If your video editor does not support RGB format, select other color format and select libx264 as the video encoder.Decrease the keyframe interval if you have trouble playing the recorded video. For 1080p60fps videos, because the bitrate is so high, even though you set the keyframe interval to 60 (default is 250), you may still have trouble playing the video sometimes, That doesn't mean that the video is broken. If you don't care about playing the recorded video or you transcode it later anyway, you can set the keyframe interval to 600.Video Encoder Settings: preset=ultrafas…
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AV1 vs VP9 vs AVC (h.264) vs HEVC (h.265): Part III - Quality

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Visual quality is somewhat subjective. However, Efforts are still being made to quantify it. There is a perceptual video quality assessment algorithm developed by Netflix called VMAF - Video Multi-Method Assessment Fusion.We tried to tune different CRF values to encode the video clips we used in previous parts. But unfortunately, we found that decreasing the CRF did not increase the VMAF score, it even dropped a little bit. We are not able to do a quality comparison at this moment.Anyway, a feature of x264 called Psy RDO caught our attention: the human eye doesn't just want the image to look similar to the original, it wants the image to have similar complexity. Therefore, we would rather see a somewhat distorted but still detailed block than a non-distorted but completely blurred block. The result is a bias towards a detailed and/or grainy output image, a bit like xvid except that its actual detail rather than ugly blocking.This preference is quite easy to understand, people wear…
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Install VMAF on Fedora, CentOS/Red Hat (RHEL)

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