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When a Blu-ray disc is being read by the Blu-ray reader in a computer or a stand-alone Blu-ray reader, does any kind of conversion or decoding process take place? I.e., is the signal in any way changed before it enters the HDMI or DisplayPort signal cable? If so, can this decoding process be performed differently by different computers, Blu-ray readers and stand-alone players?

To put it in a different way: could the use of different bluray reading units result in different ones and zeroes entering the HDMI/DisplayPort cable, or is the conversion (if there is one) always done in exactly the same way?

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closed as off topic by Renan, 8088, Ƭᴇcʜιᴇ007, Tog, HackToHell Feb 25 '13 at 12:29

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The reflection of the laser off an optical disk (whether Cd, DVD or Bluray) has to be demodulated to extract a digital signal. The output of an optical drive (which is input to the PC) is digital data, just like a hard drive. The PC host reading this data really doesn't care, other than that an appropriate filesystem layer and audio/video codec have to handle the data. Lossy codecs that decompress this data do have leeway in trying to generate the original data (i.e. there have been codec bugs that produce artifacts, the euphemism for incorrect output). –  sawdust Feb 24 '13 at 23:08

2 Answers 2

The BluRay contains compressed audio/video (e.g. H.264 video), while HDMI carries uncompressed data. This means the data has to be decoded.

On a PC, decoding is done by the player software (either using the CPU or the GPU or a dedicated H.264 chip which is probably part of the GPU). Decoders will vary across players, but that should not affect the output. However, decoders and players will often have some kind of post-processing (optional most of the time), and that will affect the output. Also, it is easy to misconfigure your output (e.g. start with "black" at level 30 instead of 0).

So I think that the drive you use for PC BluRay playback doesn't matter, but the software used does. Hardware players may vary by postprocessing (if any).

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I'd say that it depends on the computer. Bluray readers are not directly connected to the video output on a computer. The bluray acts as a storage device, storing an encoded video. Since the stored, encoded video will not change, the computer is likely to decode the video to the same pixels each time you play a bluray.

So you would expect the output to be the exact same every single time you do so. But depending on the current workload the computer has to deal with, it may or may not keep up with de decoding process. The video output might experience stuttering or screentearing. Sometimes ever artifacts when a GPU has been overclocked too much or some hardware is failing.

Some video's are encoded with an algorithm that makes it possible to define a decode 'quality'. This means the software will choose a quality based on usersettings and the amount of work the CPU or GPU can handle.

HDMI often supports an audio output, and audio is very likely to put through some equalizing and possibly some other filters. This is done with all kinds of algorithms.

Even though you might expect the exact same binary signal, it could appear otherwise. I think it's very unlikely to measure the same signal twice, but I'm not saying it's impossible..

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