Digital Video Rental for filmakers

MiniDV

The "L" cassette is about 120×90×12 mm and can record up to 4.6 hours of video (6.9 hours in EP/LP). The better known MiniDV "S" cassettes are 65 x 48 x 12 mm and hold either 60 or 90 minutes of video (11 GB) depending on whether the video is recorded at Standard Play (SP) or Extended Play (sometimes called Long Play) (EP/LP). 80 minute tapes that use thinner tape are also available and can record 120 minutes of video in EP/LP mode. The tapes sell for as little as $3.00 USD each in quantity as of 2007.

60-minute MiniDV tape will hold   approximately 13 gigabytes of data in this form of usage as the DV video format has a constant data rate of 3.6 Megabytes per second (3.6 MB/s×60 seconds×60 minutes = 12,960 MB per hour, divided by 1024 = 12.66 GB per hour).

Though originally intended for the consumer market as a high-quality replacement for VHS, L-size DV cassettes are largely nonexistent in the consumer market, and are generally used only in professional settings. Even in professional markets, most DV camcorders support only MiniDV, though many professional DV VTRs support both sizes of tape.

HDV

HDV was designed to offer existing video production environments a cost-conscious upgrade path from standard-definition (SD) to high-definition (HD) video. Since HDV operates at the same recorded datarate (25 Mbit/s) as DV, HDV recorders share the same physical (MiniDV) tape transport as existing DV equipment. For the camera, the main expense is concentrated in the optics and imaging electronics. Compared to HD video equipment built on more professional standards (such as HDCAM and DVCPRO HD), HDV enjoys a tremendous cost advantage. HDV camcorders open high-definition video acquisition to consumers, amateur videographers, and low-budget TV production.

Although 1080i HDV and DV share the same (DV) tape format and the same recorded datarate, they use different video compression technology. The DV codec uses strictly an intraframe (spatial) scheme, whereas HDV uses the MPEG-2 video format, including both intraframe(spatial compression) and interframe coding. This allows HDV to achieve its higher spatial resolution at the target bitrates of 19.7 Mbit/s (720p) and 25 Mbit/s (1080i). Compared to more expensive HDCAM and DVCPRO HD equipment, HDV suffers from significantly more spatial and temporal (motion) artifacts.

As a consequence of interframe (temporal) compression, HDV editing is more complex, and introduces some editing distortion near splice points (due to the interdependencies between video frames). Compared to conventional SD DV, HDV offers much higher spatial resolution and higher overall fidelity, so most observers are willing to accept these problems. While standard definition MPEG-2 broadcasts typically use only 2 to 4 Mbit/s, the 25 Mbit/s of HDV enables both high-definition video storage and a lower degree of compression artifacts, with much less visible artifacts. HDV audio uses lossy compression to reduce the audio bitrate to 384 kbit/s. DV audio uses uncompressed 16-bit PCM at 1536 kbit/s. As a result, HDV audio is technically inferior, although MPEG-1 at 384 kbit/s is regarded as 'perceptually lossless.'

Canon has started to ship consumer camcorders that are capable of 24 progressive frames per second. That is, 24 progressive 1080 frames are captured per second, each of which is stored as two coded fields in a 1080i bitstream. This allows decoders to display the progressive frames as full resolution 1080p frames at 24 frames per second or to use "2:3 pull-down" display to show it on a 60-field per second interlaced display.

Since HDV and DV use the same DV25 tape transport, at the same linear speed, recording times for DV and HDV are identical. That is, a 60 minute MiniDV cassette can store 60 minutes of either DV or HDV footage. As of yet, no HDV cameras can record HDV at LP speed, so the maximum record time on one tape is 80 minutes, as opposed to 120 with an 80 minute tape at LP.

Because HDV uses the same tape form factor as DV, users should be able to use any high quality MiniDV tape in their HDV camcorder. However, because HDV has a lower tolerance for drop-outs because of its long-GOP compression, many HDV users purchase either "master" quality Mini-DV tapes or specially formulated HDV tapes.

HDV compression

Although HDV and DV share the same tape format and the same recorded datarate, they use completely different video compression technology. The DV codec is strictly an intraframe (spatial) compression. Each DV video frame is recorded as an independent picture, with a fixed bit allocation and uniform placement on the videotape. The HDV codec is based on MPEG-2 video compression, which employs both intraframe and interframe (temporal) techniques. Interframe compressors store only a fraction of the frames in a video as independent pictures -- called I frames -- and encode the remaining frames as changes relative to them.

Consequently, HDV frames vary in size depending on their prior and future neighbors. In HDV 1080i, one in every 12 (25fps) or 15 (30fps) frames is an I frame. In HDV 1080p, one in every 12 (25 FPS) or 15 (24 or 30 FPS) frames is an I frame. In HDV 720p, one in every 6 (24, 25, or 30 FPS) or 12 (50 or 60 FPS) frames is an I frame.

MPEG-2 video enables HDV to achieve a much higher compression ratio than DV, 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. Motion artifacts are imperceptible for static shots and gentle pans, but may become increasingly detracting as motion complexity increases. For example, a moving riverbed may exhibit regions of picture breakup, depending on its portion of the total screen area. It is important to view these limitations in the proper context. Lighting, chroma content, camera motion, etc all play a role in the potential for artifacts.

Dropouts or errors in the compressed video bitstream affect HDV much more severely than DV. This is an unavoidable characteristic of interframe compression. Since frame data affects multiple frames (and not just the one it originated from), a dropout will impact all dependent neighbors. Frame-accurate editing is also made more difficult by the MPEG-2 codec. Any modifications to the video sequence require the surrounding group of frames to undergo a complete (and lossy) decompression/recompression cycle. However, virtually all professional non-linear editing software is now designed to work flawlessly with HDV.

For all its limitations, HDV is quite stunning on HD displays. Although free of motion-induced artifacts, DV tends to look fuzzy when scaled up to HD resolutions. Subjectively, most observers are willing to accept HDV's visual artifacts in exchange for a more detailed picture.

Resolution and aspect ratio

In HDV, the video frame is defined to have an aspect ratio of 16:9. Permitted resolutions are 720p and 1080i.

HDV 720p uses a resolution of 1280x720 square pixels. HDV 1080i uses a resolution of 1440×1080 pixels, but is still displayed with an aspect ratio of 16:9 (like SD widescreen formats, it uses a pixel aspect ratio of 1.33 instead of 1.0).

DVCAM

Sony's DVCAM is a professional variant of the DV standard that uses the same cassettes as DV and MiniDV, but transports the tape 50% faster. This leads to a higher track width of 15 micrometres. This variant uses the same codec as regular DV. However, the greater track width lowers the chances of dropout errors. The LP mode of consumer DV is not supported. All DVCAM recorders and cameras can play back DV material, but DVCPRO support was only recently added to some models like DSR-1800, DSR-2000, DSR-1600. DVCAM tapes (or DV tapes recorded in DVCAM mode) have their recording time reduced by one third.

DVCPRO P2 

(P2 is short form for "Professional Plug-In") is a 

professional digital video format introduced by Panasonic in 2004, and especially tailored to ENG applications. It features tapeless (non-linear) recording of DVCPRO or DVCPRO50 streams on a solid state flash memory card. DVCPRO HD recording on P2 is possible with the Panasonic AG-HVX200. The P2 Card is essentially a Raid of SD Memory cards with an LSI controller tightly packaged in a die cast pc card (formerly PCMCIA) enclosure, so data transfer rate increases as memory capacity increases. The system includes cameras, decks as drop-in replacement for VCR's, and a special 5.25" computer drive for random access integration with NLE systems. 

The cards can also be used directly where a PC card slot is available, as in most laptops  as a normal disk drive, although a custom software driver must first be loaded.

Since the memory capacity of the P2 card is relatively low as of January 2006, 2GB [4×512MB cards], 4GB [4×1GB SD cards] and 8GB [4×2GB SD cards] cards are available), cameras, decks and drives have multiple slots, with the ability to span the recording over all slots. This way, effective recording time is multiplied, allowing up to 80 minutes on five 4GB cards in normal DVCPRO 25 mode. 

Cards are recorded in sequence, and when a card is full, it can be swapped out while another card is recording, allowing unlimited recording time assuming an adequate supply of cards is available. If a card is partially full, the deck will record only until it is full. Unlike tape, old video cannot be recorded over accidentally. Old footage must be manually deleted.

The first pieces of equipment released by Panasonic which use the P2 format included the AJ-SPX800 (a 2/3" broadcast camcorder for ENG and EFP applictions), the studio recorder AJ-SPD850, the AJ-PCD10 offload device (basically, a five-slot PC card reader with USB interface designed to fit a 5-1/4" IT systems bay), and the memory cards themselves - AJ-P2C004 (4Gb) and AJ-P2C002 (2Gb). The AG-HVX200 consumer/semipro camcorder is not, despite common belief, the first P2 device, but it is the first to offer multi-rate standard and high definition recording.