And why there are some 4-5 GB size blu ray movies available for download? If both the 50GB and 5GB versions are 1080p, what has been lost due to compression? Will there be a huge difference to visual & audio?
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EDIT: Thanks everyone, now I have a new found perspective on quality.
In: Technology
The size of blu-ray movies is driven by the size of the medium. There is no advantage of just using half the space of the disk when it cost just as much to produce a full disk. So the producers make sure to use compression settings which will make the movie take up the entire space of the disk.
Compression settings is quite complex. The number of pixels is just one setting and relatively insignificant to the quality at that. In reality the compression algorithms split the image into blocks and those blocks into smaller blocks and so on. The more bitrate the more details it can use per block making the result more and more like the original image. It is possible to make a low bitrate high resolution video but it will not look as good as the original. So when people compress a 50GB movie into 5GB they are losing a lot of detail. But the compression algorithm is quite good and you just lose the harder to spot details. You might still see lots of compression artifacts in some scenes though but the movie is perfectly watchable for the most part.
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