HD compromises – “near HD” – “HD Lite”
Aug/091
High definition video imposes huge requirements on bandwidth for the video data stream. The requirements are so high that many enthusiasts consider the bandwidth in the BluRay(40mbps) and HD-DVD(28mbps) to be inadequate to get a “decent fidelity” HD video playback. Well this is formally true … in some cases. In practice we’ve lived with the low standard definition(SD) content for more than two generations now. If the technology still struggles with single consumer solutions, what do we do with HD video on the web then? Besides the raw bandwidth there are other solutions improving the odds in our favor a bit.
The “modern” h.264 (MPEG4/VC1) codec used for nearly all “higher” resolution video on digital devices and the internet has several major benefits in comparison to previous generation codecs.
First and foremost IT IS A STANDARD! It may not sound like much, but that’s the basis on which all hardware and software vendors step. This ensures a variety of tools and hardware acceleration support, that wouldn’t happen otherwise. Without hardware acceleration you can forget about any video playback above 720p resolution.
Second there are better “tools” available in the codec specs to allow improved bandwidth allocation where it counts most and thus attaining better visual quality within the same bandwidth. With loss based compression algorithms this is what really counts, and it’s what makes the difference between two codecs actual results.
What happens in practice is that in many cases you can get better visual quality with a h.264(MPEG4) stream than a MPEG1 stream with double of it’s bandwidth. There is less(half) information stored in the h.264 stream, but there is more information that actually counts for the visual quality. The actual benefit from codec improvements depends very much on the use case and there are specialized codecs that outperform h.264 in many cases like animation, fast motion and low bitrate streams for example.
Third h.264 is a more flexible container format and allows deblocking techniques. Deblocking means that if a player doesn’t support some particular compression feature it may be “skipped” and the playback to continue. This also means low power devices can reduce the quality and still be able to play the stream. This concept allows for better standard acceptance and content interchange.
VP6 Flash video
Wen it comes to web, video flash video holds the big share … and for a couple of good reasons. If you, your service provider or your users are tight on bandwidth VP6 is still the best choice for near HD content. Some good time will have to pass before h.264 and theora tools mature enought to beat On2 VP6 on low bitrates.
The near HD / lite HD compromise
It is impractical in today’s web to mass publish high bitrate streams. The practical limits for different video hosting/video sharing services are different but they are usually bellow 2mbps with a high margin of up to 4mbps. If you use up to 540p resolution these rates can provide similar fidelity to the 9mbps HD-Lite TV broadcasts many people complain about.
Near HD is a marketing term used by many providers to indicate some support for higher resolutions. Near HD is used in reference to resolutions from 408p(720×480) to 720p(1280×720).
HD lite is also a market term related to horisontal resolution downscale done by some HDTV providers in order to sava bandwidth. With HD-Lite there is a pixel aspect ratio different than 1:1. i.e. the pixels are rectangles instead of squares. Common HD lite resolutions are 1440×1080 and 1280×1080 which are downscaled from 1080p(1920×1080) and are still representing a picture with aspect ratio of 16:9.
On the web many tricks have to be used in order to get better results within the technology limitations. Here are some tricks for getting better results when there are bandwidth restrictions imposed by your provider or your users’s connecitons:
- Never use resolutions higher than 720p(1280×720). Most user’s(>70%) can’t view that resolution and will downscale to 720p or lower anyway.
- Never use more than 30fps framerate on the mass web! Many people will get bad playback and it is a waste of bandwidth in general.
- If it is a slow motion video or you need to keep the resolution higher use slower framerate. 15FPS is quite good for many cases where resolution counts.
- If you have a fast motion video keep the framerate at 30fps (or 25fps both are good and you should not change between them) and lower the resolution! A 480p fast motion video looks far better than a video with the same bandwidth at 720p!
- When changing framerate only downscale and only by a whole number! If you have a 30fps source you will get better quality with 15fps than with 20fps. If you have a 25fps source you should scale to 12fps instead of 15fps.
- Do not insist on your content quality, but rather on your user’s experience! Many web users will access your content through slow connections and with low power devices like netbooks, PDAs and cell phones(like iPhone/gPhone/win mobile). These web users can hardly handle anything beyound 405p(720×405)
- Finally, respect your network! YouTube is losing half a billion and all other providers face huge costs for bandwidth and infrastructure, so the fact that they provide you a 540p resolution capability is a very nice thing on their side. We will all get to 1080p eventually. Be patient and make sure your content deserves it
