Video Formats by Claire Buckley

Standard Definition and High Definition

Over the last few years, recording video in the High Definition format has become much more affordable, and accessible - no longer is it the singular domain of broadcasters and their professionals. The introduction of the HDV format in particular has seen a new entry into what is often described as the Prosumer market.

HDV as used by Sony and Canon produces a native image size of 1440 pixels wide (horizontal) by 1080 pixels high (vertical) in the 16:9 widescreen format. In comparison, a DV image size is 720 pixels wide by 576 pixels high with a 4:3 format - the aspect ratio of earlier television screens.

Available also is the XDCAM and AVCHD formats which produce an image size of 1920 pixels wide with the same height, 1080 pixels. Often preferred but not exclusively required by broadcasting organisations for HD production, the format does present some challenges when it comes to editing and file handling on a PC or MAC. A solution is to convert the raw files to a more manageable format.

Broadcast Acceptable HDV Format

The HDV format is accepted by broadcasters with a number of high profile and network produced programmes in distribution using HDV format content. Among these were a great number of the HD programmes made for The Discovery Channel. HDV Camcorders are smaller and lighter in weight and are often preferred in locations of limited space, or where there needs to be less intrusion during recording.

As can be seen, larger formats (Resolutions) such as 1440x1080 and 1920x1080 have more data and take up greater file space.

One of the main advantages of HDV from a cost point of view is the ability to capture the digital data using Mini DV Tapes in addition to solid state storage methods. Such tapes should not be confused with the old analogue tapes. MiniDV tapes record digital data, are relatively cheap and of excellent quality, with the advantage of being able to easily archive and source the original material for later use. Alternative digital storage in hardware often called a tapeless environment is still relatively expensive, insecure and inflexable often requiring large amounts of hardware storage memory to archive the original material. There are no noticeable quality differences in the final material using tapeless or tape storage methods.

For further information about HDV you can read more by going to HDV, Wikipedia

Progressive or Interlaced?

Television transmissions and screens of older type television receivers called Cathode Ray Tubes (CRTs) use an Interlaced method of display. This refers to the frame or vertical element and still applies even to more modern Plasma and LCD screens - the transmission is still an interlaced format. Simply, the television image uses odd and even numbered fields simultaneously combined to make a single frame of a television picture. The advantage of this in the real world is that the television signal uses less bandwidth, that is the amount of space allocated for the television transmission.

In the UK, the early receivers were locked or synchronised to the mains power AC frequency of 50Hz. In North America this was synchronised to a mains frequency of 60Hz. The frame rate is the reason that some people are able to perceive a small amout of flicker in the displayed image - the eye is fooled into seeing a complete image, not two simulatenous images. With higher frame rates, the effect is less pronounced.

With the advent of computer monitors and LCD display screens, the Progressive scanning system was introduced. This eliminated the screen flicker effect with material viewed recorded in the Progressive format. Viewing Interlaced material on a Progressive scanning system like a computer screen shows as jagged edges during scenes where there is fast movement - the interlacing becomes very noticeable. However, HDV and other formats provide the ability to record in either Progressive or Interlaced and at different frame rates, depending upon the requirements of the delivery system and creative needs - the often described Filmic Effect using 24p (24 frames per second, the film frame rate with a progressive scanning system).

Blu-Ray DVD or Standard DVD?

Because the HDV format picture contains much more digital information (data) compared to a Standard format DV picture, a new type of storage and playback system is required. The introduction of Blu-Ray or BD, provides a much larger storage capacity (up to 25 Gigabytes - single layer, 50Gb - double layer) compared to the Standard DVD format (up to 4.75 Gigabytes - single layer, 8.5 Gigabytes - double layer). In addition a higher data Read-Write speed (Transfer Rate) can also be accomplished - that is the ability of the system to sample and transfer much larger amounts of information over a period of time.

At Moving Memory we are able to record HD content for Standard format playback using a Standard DVD in order to minimise cost, as Blu-Ray writeable DVDs can be expensive. By using specific coding techniques, we retain a very high Transfer Rate to make sure the quality is the best it can be on the Standard DVD system. We like to see what goes in, is of similar quality (within acceptable allowances) as that which comes out. INPUT >> minimal losses and artifacts >> OUTPUT. This same philosophy relates to the whole of our workflow.

If HD material is required to be played and viewed as a true HD programme on a HD television, then we use a Blu-Ray DVD.

More information about Blu-Ray can be found by going to Blu-Ray, Wikipedia.