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Forums Compression Techniques New – help with basics of codecs, formats, etc.

  • New – help with basics of codecs, formats, etc.

  • Mike Nibeck

    July 6, 2009 at 1:46 pm

    I’m poking around threads, and picking up bit of information here and there, but it’s such a daunting and complex subject. I plan on grabbing some of the DVDs from the store (“A Guide to Creating Web Video”. etc), but I’m also trying to get the basics down.

    Anyone care to offer up some basic info for things like:
    – Compression
    – Containers
    – File formats

    More important how they relate to one another.
    H.264 is a codec, but not a file format?
    Flash is a container, but not a codec?
    .mov vs. .flv?

    All terribly confusing.



  • Brian Alexander

    July 7, 2009 at 1:56 am

    I would suggest you start reading other postings in this forum just to read them. Soon things will start making sense.

    Digital video is one of those subjects where the more you learn the more you will begin to understand which questions you should be asking which will lead to more precise questions and answers and more confusion until one day all the information will build up in your brain and just before you feel like you’re going to explode you will reach your stage of enlightenment.

    I have been regularly studying Digital Video for quite some time now and I’ve come to a point of confident knowledge but it does take time. I am still discovering things I did not know all the time. The way the industry is changing I doubt anyone knows everything. Just when you think you have all the answers they change all the questions.

    Here are some basic answers to your questions:

    Container Formats optimize video for specific applications. For instance, MPEG 2 is wrapped in a VOB format for DVD and it is wrapped in a GXF format for some broadcast media players and servers.

    Compression is deep. One of the most widely used forms of compression is GOP (group of pictures). Basically, instead of every frame of video being an entire picture (like a strip of film) a GOP will use one frame, an i-frame, as reference then only encoded the moving parts of the picture of the subsequent frames (p and b frames) before creating another i-frame. This is basic information and each CODEC has its own specific ways of using GOP based compression; this is a study in and of itself.

    Compression comes in many forms besides Codecs (COmpressors DECompressors): Interlacing, Chroma Subsampling, and odd pixel aspect ratios are also forms of compression (just to name a few).

    FIle Formats? This is the same as a container.

    Here are a few extra tidbits to get you on your way:

    NTSC SD resolution is 720 x 486 analog and 720 x 480 digital. It is the same pixel count for 4:3 and 16:9.

    Although 1080 HD video is displayed using square pixels at 1920 x 1080, not all HD codecs use that pixel space: some are 1440 x 1080 or 1280 x 1080!

    720p provides a higher quality image than 1080i! (I’m sure some will argue with me here but at any given instance in 1/60 of a second, you will find a full image at 1280 x 720 and half image at 1920 x 540.)

    An HD image in ProRes (SQ) @ 147 Mbps and h.264 @ 8 Mbps taxes the computers processor about the same. Why? h.264 requires decoding and ProRes is all i-frame based – nothing to decode.

    I could go on…

    Just remember, Wikipedia is your friend.

    Brian Alexander
    Sr Video Engineer
    Freeman AVS

  • Mike Nibeck

    July 7, 2009 at 2:25 pm

    Brian, excellent info, thank you. I will certainly keep reading and learning. Never enough time in the day 🙂 I was actually involved in some digital video projects many many years ago. Working with items like the VideoVision Studio cards, etc. Long time ago, much forgotten.

    Thanks again!


  • Daniel Low

    July 8, 2009 at 2:18 pm

    [Mike Nibeck] “Working with items like the VideoVision Studio cards”

    I used to sell and support those back in the day as well as VideoVision Telecast which was way ahead of its time.

    Two years from now, spam will be solved. – Bill Gates, World Economic Forum 2004

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