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Digital Video Details

Just a few years ago, the work of amateur and professional videographers was separated by a vast difference in image quality. This was primarily due to the limitations of consumer tape formats. But times have changed. Digital video for consumers encompasses all of the 25Mbps DV formats. So, if you have a DV camcorder, be it Mini DV or Digital8, it uses the same recording scheme that professional DVCAM (Sony) and DVCPRO (Panasonic) camcorders employ. That means your $600 Mini DV camcorder records the same image data as a $10,000-plus DVCAM or DVCPRO model that the pros use. Consider the following similarities:

  • Mini DV, Digital8, DVCAM and DVCPRO all use the same 25Mbps data rate.
  • They all use the same 5:1 DCT intra-frame compression scheme.
  • They all use the same 4:1:1 sampling scheme (NTSC).
  • They all deliver the same 720x480 resolution (NTSC) and frame rate.
  • IEEE 1394 (FireWire) is supported in all four video formats.

    Compression
    Visual and audio information that comes into a camcorder is encoded into a digital format. Raw or uncompressed, full-frame size, full-frame rate NTSC video data might occupy 30MB (megabytes) for every second of video, which is a huge amount of space. For pragmatic reasons, therefore, the video is usually compressed. This compression can result in a loss of image quality and can be very computationally intensive, depending on the complexity of the compression scheme. Digital Video (DV - with a capital "D" and a capital "V") uses a compression scheme that is relatively lossless and is not difficult for a computer to work with. The data compression ratio for DV is about 5:1, which results in one second of video taking up approximately 3.6MB of disk space. Expressed more appropriately in terms of megabits per second, the data rate for DV is 25Mbps.

    While there are many other digital video formats, such as DVCPRO50, which has a 50Mbps data rate, when we talk about DV we are talking about a 25Mbps data rate. Digital8, Mini DV, DVCAM and DVCPRO all have the same data rate and, therefore, the same potential level of quality. DV compression happens only within individual independent frames (intra-frame) and uses a Discrete Cosine Transformation (DCT) algorithm, which is the mathematics used to compress …

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    • Charles Bloodworth | August 2002

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