Blu-ray won the format war.
HD DVD players were the first one to reach the market in April of 2006 and captured the initial market share. However. Blu-ray has prevailed. Although HD DVD lost the format primacy a small amount of titles is still being released on HD DVD in early 2008. The amount of new releases is likely going to dwindle in the near future.
Blu-ray is capable of higher storage (100GB on quad layer discs) which is an important factor when it comes to HD size picture.
While a consumer browsing the menus of the same title on Blue-ray and HD DVD may not see any noticeable difference, the underlining architecture is very different between the two formats. This inherent difference makes it impossible to author a disc for both formats in a single process.
Alternate DVD formats created specifically for HD are VCD HD, HD VMD, EVD, FVD. None of these formats are significant competitors in the United States.
Disable unauthorized copying.
Content copy protection in consumer HDTV has another layer of protection previously unavailable in the SD world.
HDCP system scrambles the high definition signal between devices such as HDTV cable box and the monitor. Each device in the chain must be capable to “speak” the same encryption language. If a recording device such as a recordable HD DVD is introduced in the chain it also has to be able to decrypt the signal in order to perform the recording.
In case the device can not decrypt the signal HDCP protocol is intelligent enough to allow the downstream device to receive standard definition downconversion of the signal.
Many less expensive consumer displays that bear “HD Ready” label are incapable of displaying the full 1920×1080 raster size of the largest HD standard. They internally downconvert larger image to the maximum pixel resolution they can display. On such monitors it may be difficult to discern any visible difference between 1080 and 720 size signals.
Another set of numbers commonly seen on HD monitors is contrast ratio. This ratio describes the maximum dynamic range between darkest black and the brightest white.
Proper delay management is crucial.
HD size video takes a good amount of processing power. Almost all devices in signal chain will introduce noticeable video delay. While picture is “held back” the audio is passed without delay resulting in a loss of sync. The effect is cumulative in subsequent passes. Before you know it even a casual observer will report that a sound of a closing door is heard before it is seen.
Most flat screen displays also introduce delay which makes them difficult to use in a professional environment. Proper sync is critical for editing, sound and multi-camera control rooms (trucks).
The issue can be mitigated to some extent by placing proper audio delays to “hold” the audio signal back in line with corresponding video.
Asked to deliver 8 tracks of audio on HDCAM tape? Tough luck, but there may be a way.
Video tape recorders (VTRs) support different numbers of audio channels based on the format.
HDCAM 4 tracks
HDCAM SR 12 tracks
D5 8 tracks (older ones up to 4 tracks)
DVCPRO HD 8 tracks
VTR formats not listed here are not likely to be requested as delivery formats. Most common mastering format at this time is D5 and 8 channels is adequate although not perfect.
HDCAM’s 4 channels may not be enough in some situations. If you need to deliver 5.1 mix on an HDCAM tape how do you record 6 channels on a 4 channel tape? Dolby E process allows you to squeeze 6 digital audio channels into 2 channels.
Once encoded you can not play such audio back without a Dolby E decoder. The master can not be easily downconverted or run through standards converter while maintaining the integrity of the Dolby E tracks.
Standard for NTSC DVDs and beyond.
AC-3 (AC3) is a Dolby file format engineered to provide high quality 6 discreet channels of audio. The encoding is compressed in order to maximize limited bandwidth of the delivery media. AC-3 also supports stereo left & right configuration as well as mono configuration.
The system is in widespread use in movie theaters, NTSC DVDs and Digital TV broadcasting.
Commonly used in theaters and at home.
5.1 surround sound specifies three front channels, two rear surround channels and a low frequency channel totaling 6 discreet channels. It is commonly provided on DVDs and is used in Digital Theater System (DTS).
The track layout:
LFE (Low Frequency Effects)
Ls (Left Surround)
Rs (Right Surround)
HD deliveries often require 5.1 audio mix in addition to Stereo Left & Right Composite Mix. In case M&E is required another set of 5.1 M&E tracks will be needed totaling the number of tracks to 16. Additional audio can be folded into a smaller number of tracks using Dolby E process or the tracks can be delivered on an audio tape such as DA88.