HD Voodoo?


More and more these days, movies and other media are being served to us for purchase or rental via online streaming or downloading.  This recently got some friends and me discussing the quality of such media sources.  Now, it seems you see the “1080p HD” label on just about EVERYTHING.  I wouldn’t be surprised if Detroit’s next car model is the “1080p”.  But what does “1080p HD” mean, really, and should it mean something else?

All “1080p” really means is that the resolution of the media is 1920×1080 pixels, and that it is progressive-scan, not interlaced, video.  Labeling something as 1080p does not in any way (unfortunately) indicate the quality of that video.  Although the FCC never set any guidelines on what qualifies as true high-definition video other than just resolution, I think that slapping the “HD” label on something should mean more than pixels.  One should be able to expect a stunning picture when you see the “HD” label.

In theory, one could take a 480p x 720 (that’s standard DVD resolution) video and scale it to a resolution of 1080p with no interpolation, and you’d get a 1080p resolution picture with absolutely zero change in apparent picture quality over the original, but substantially larger in file size. I highly suspect that a lot of the “1080p” content we see out there these days is what some might call “pseudo-HD”, and probably barely (if at all) better than a decent DVD picture of the same material.

For example, take the video streaming site, vudu.com, and Vudu’s ads for 1080p “instant” streaming.  Blu-ray discs can have a capacity of 50GB, with the movie alone taking up 30~40GB, and a bitrate anywhere from 15Mbps to 40Mbps.  How can a movie that large be available “instantly” with a standard broadband (e.g. 2Mbps speed) internet connection?  Answer: it can’t.

Warning: the following may seem like I’m picking on Vudu.  I’m not.  They offer a really cool, high-quality service.  I am picking on their marketing, and maybe a bit of their technological choices though

I think a lot of people forget that there’s more to HD picture quality than resolution. Bitrate is just as, if not more important than resolution. The only way these sites are streaming 1080p instantly is with a relatively low bitrate.  A low bitrate means high compression, and low picture quality, regardless of the resolution.

Think about how stunning a good Blu-ray movie is.  To me, it is surprising how much better some BD (Blu-ray disc) movies are than even a good off-the-air (OTA) HD broadcast. This is not because the resolution is different (1080i/60 from an antenna is easily and losslessly converted to 1080p/24 by most decent HDTV de-interlacers) but because the bitrate for a good BD flick is often twice that of most OTA HD broadcasts, and even more than twice the bitrate of most cable and satellite HD signals.

OTA 1080i HD signals max out at around 19Mbps, with most averaging around 12~15Mbps depending on how a given station allocates their bandwidth. Vudu however, based on their system requirements, caps its instant-HD bandwidth at just 2Mbps (the minimum bandwidth one must have to use their “watch instantly” feature). That’s less bandwidth (bitrate) than virtually all DVD’s have.

The trick of course, is new more modern codecs. DVD (and OTA HDTV broadcasts) still use the now outdated MPEG-2 codec, while everyone else (cable, streaming, and satellite) have switched to MPEG-4 or similarly modern codecs (H.264, etc.)  So 2Mbps gets you a lot more picture quality with H.264 than it does with an MPEG-2.  Okay, but most Blu-ray discs use either VC-1 or AVC (i.e. H.264) codecs.  Which brings us back to the question, how can you promise 1080p HD with 3Mbps bandwidth?  Even with buffering and the newer codecs, we’re still an order of magnitude away from the 30+ Mbps rates of many Blu-ray movies.

Don’t get me wrong – Vudu definitely has a great service. But I’m skeptical about their “HD 1080p” tag and its quality. (To be fair, it’s not just Vudu, Apple is touting HD streaming now too.)

Anyway, according to Vudu’s site, the minimum bitrate necessary to “watch instantly” is 2~3Mbp. This includes their 1080p HD content. It does NOT include however, their premium quality HD content, called “HDX”. HDX is just the tag they’re using for 1080p HD videos encoded with H.264 technology at a higher bitrate. HDX movies require 2 to 3 hours of buffering time before the box will let you watch the movie. They claim “near Blu-ray quality” and “virtually artifact free”. Those words sound like they’re hedging to me.  If we’re comparing to Blu-ray as a quality standard (which Vudu is doing), do the math: 2-3 hours of buffering before you can watch a HDX quality movie means that the file size is still only around 4~8GB.  That’s the size of a standard DVD movie.  Again the new codecs get you better picture quality for the same file size, but Blu-ray moves use these codecs and are 5 to 10 times larger in file size.  To call these “near Blu-ray quality” is really stretching the truth, in my opinion.

Regardless, HDX movies are pretty good, considering they are quasi-streamed.  You can order one from your work PC at 5 pm, and watch it by the time the kids are in bed and the dishes are done.  That’s really cool.  But is what you watch really comparable to a real Blu-ray disc experience?  I really don’t think so, especially on a large screen.

Vudu’s HDX format is “recommended for 40 inch and larger HD screens” which implies that their standard “HD” videos are NOT recommended for screens larger than 40″. Why? Given the low bitrate, this is probably because they are loaded with compression artifacts like macroblocking.  What I want to know then, is why do they waste bandwidth and file size making these videos 1080p resolution?  The same overall picture quality could most likely be had with lower resolution, the same or higher bitrate, and smaller overall file size.

Anyway, I guess my point is: buyer beware when you see “1080p HD” plastered everywhere.  Check the bitrate!  What are your experiences with streaming of so-called “HD” content?  What so you see as the future of streaming HD content to consumers vs. going to Blockbuster or Netflix and getting movies on a disc? Share your thoughts in the comments section below!

Kieran Coghlan