HDV Compression

HDV is based on MPEG-2 video, which compresses data both within each frame (intraframe/spatial compression) and between frames (interframe/temporal compression). This is the same type of compression used for DVD video and many network TV broadcasts, and allows HDV to achieve high spatial resolution at low data rates compared to other HD recording formats. HDV 1080i uses a recording data rate of 25 Mbit/s (3.125 MB/s) while HDV 720p records at 19.7 Mbit/s (2.46 MB/s) compared to data rates of 50-100 Mbit/s and up for other HD formats.

Using MPEG-2 video enables HDV to achieve a higher compression ratio than recording formats without interframe compression, but at the cost of motion-induced artifacts in scenes of complex motion. The artifacts are a limitation of the compression technology and bitrate allocated to the video bitstream. Scenes with little motion are easier for HDV to compress than scenes with rapid movement, strobing lights, or other complex activity. For example, a scene of a moving river may exhibit regions of picture breakup, depending on the amount of movement in the water. A static scene of a mountain countryside, by comparison, will exhibit none of these visual problems.

Interframe compression also means that a recording dropout in HDV can affect several frames of video rather than just one, since the compression introduces dependency between frames. Hence it is best to use high-quality tapes for HDV recording such as "master quality" Mini-DV or specially formulated HDV tapes, and limit the reuse of tapes. Some users have got good results with HDV using generic Mini-DV tapes, but this is not generally recommended.

For audio, HDV uses (MPEG-1 Layer 2) compression to reduce the audio bit rate to 384 kbit/s, compared to 1536 kbit/s for DV video and 1411 kbit/s for audio CDs. This makes HDV audio less desirable for situations where sound quality is critical, but MPEG-1 audio at 384 kbit/s is considered 'perceptually lossless.' For general video recording with an on-camera microphone, HDV audio is not a significant limiting factor.

It is important to view HDV's compression limitations in the proper context. Other HD codecs using lower compression ratios need more bandwidth and storage capacity for a given amount of video, requiring significantly more complex and expensive recording solutions. For example, the Panasonic AG-HVX200 camera uses memory cards which can cost over $50 per minute of recording capacity, compared to a few dollars per hour for Mini-DV tapes. This cost differential has helped make HDV a popular HD recording format for consumers, independent videographers and low-budget TV programs.

HDV has some similarities to the more professional XDCAM-HD format, but the latter uses higher data rates for both video and audio signals.