DVD replaced VHS, then Blu-ray came along in all its HD glory and now we have 4K Blu-ray taking the crown as the highest-resolution disc you can get – until 8K Blu-rays come along at some point.
These discs look alike and are the same physical size, so should you be rushing out to replace your film collection every time a new format comes out? Let's look at the differences.
The difference between the three different types of disc is how much data you can store on them. They're all the same physical CD-size we've been used to for years, regardless of the format.
Think of a movie or a TV show as a file on your computer – the higher the resolution, the sharper the image and the more space it takes up on the disc:
4K resolution films take up a massive amount of memory when compared with a 480p DVD file and you could never fit one on to a DVD disc. But a higher resolution doesn't necessarily mean great picture quality (keep reading to find out more).
Higher resolution makes for a sharper image, that's a given. But when it comes to colour and contrast, things are less certain.
How a film is mastered for each format makes a difference to the quality. A Blu-ray version of a film could have rich, vivid colours and a finely balanced contrast, while the 4K version could look washed out and bland. This is more of an issue when an older film that was never released in 4K, or even HD, before is remastered to take advantage of the higher-resolution format. If the remastering is done poorly, then you'll notice the problems with colour and contrast.
It's a hit and miss technology, though. When used badly it can make the picture too dark or bright, which blocks all that lovely 4K detail.
4K Blu-rays tend to have more advanced audio processing and formats, such as Dolby Atmos, DTS:X and other formats that allow for less compression of the sound. Which should mean higher quality.
These processing technologies could feasibly be on Blu-rays and DVDs, too, but often they are saved for the 4K releases.
The back of a Blu-ray box will tell you what audio formats and processing is on the disc.
If you have a DVD player, then you'll only be able to play DVDs. But Blu-ray players and 4K Blu-ray players are usually backwards compatible with the lower-resolution discs.
Not a DVD player, there's really no point. Very few are still made and we don't test them any more.
Ideally, you should buy a 4K Blu-ray player. Despite some 8K TVs now being released, 4K will be the main resolution used by the TV and film industry for years to come.
If you don't have a 4K TV already, then it's likely that you will when you next upgrade, and a 4K Blu-ray player will let you make the most of the display, as well as let you watch your existing Blu-ray and DVD collection if you choose the right model - use our to help you.
4K Blu-ray players are still expensive, though, so don't rush out to buy one if you're not mad keen on buying films at the highest resolution available. The cheapest we've tested is around £150, while a good-quality HD Blu-ray player for around £60.
As 4K Blu-ray players and discs become more common the costs will come down. This happened when Blu-ray was taking over from DVD. Blu-ray discs and players cost a fortune during the transition, but now they cost roughly what DVDs and players did then.