DisplayPort to HDMI adapters are necessary when you have a DisplayPort (DP) output, like a computer, and a high-definition multimedia interface (HDMI) input, like an HDTV. The computer industry has embraced DP, but the television industry has not. Consumers should note that the need for DP-to-HDMI is uncommon because most computer manufacturers who support DP also support HDMI, DVI, VGA, S-video and perhaps even RCA and SCART.
The notable exception to this rule is Apple. They generally prefer to use the mini versions of DisplayPort (mDP) and DVI (mDVI) at the exclusion of all else. Further complicating matters is that Apple’s port implementation of mDVI does not include support for audio. This was also the case with DP until the standard changed and somewhat forced their hand. Apple began adding sound support for mDP in 2009, and by the end of 2010, their entire lineup had it.
If you have a device with support for DP but not for HDMI, then it is very important that you establish whether your particular implementation has support for audio. If not, then like with a VGA or SCART port, you must output the sound independently. Sound isn’t a requirement, but of course, video without sound is only useful in certain scenarios. DP adapters are available with digital outputs, analog outputs and USB outputs for handling sound.
It is important to understand that VESA created DP not to compete with but to complement the high-definition multimedia interface. The reason why that’s important is that there is no conversion in the DP-to-HDMI exchange. If you have a 1080p source, a 1080p display and a 1080p rated cable, then you’ll have a perfect 1080p result. This is the reason to choose Mini DisplayPort or DisplayPort to HDMI over DVI or RCA or other display standards.
Cable rating is another important issue. Most manufacturers rate their cables at 1080p. However, some rate for 720p, and some outputs only deliver 720p, such as many of the MacBooks prior to 2009. The good news is that it is fine to use a 1080p adapter with a 720p source. In fact, you’re better off opting for it for the sake of future compatibility. The exception would be when you can significant money, but these days, that is rarely the case.
Something else to keep in mind when choosing your DisplayPort to HDMI adapter is cable distance. Most people use these adapters to connect a laptop to a TV and thus distance isn’t an issue. However, the DP standard advises no more than 50 feet, or approximately 15 meters. When using the DP connection for video and sound, it is best to avoid anything greater than 10 feet. If you need more, then it would be wise to buy a booster cable.