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  • Wednesday, November 16, 2005

    Converting video capture to VCD format


    Question : My laptop has over 700 mega-bytes of random access memory. I'm using a software to convert video camera capture to VCD format. Which format do I need to choose before I start capturing the image?

    Answer : Since you're going to be recording to video CD, we will recommend MPEG-2. Actually, we recommend MPEG-2 as an all-purpose general format. It's a fairly good compression protocol and should only need to be converted if the video is going to be recorded on a "standard" VCD.

    Question : During conversion from a 60-minute tape, it needed almost a whole day to complete the job (from image capture to rendering to copy to VCD). How can I cut down on the time taken?

    Answer : It's not the capture that takes time (which takes place almost instantaneously), but it's the conversion and burning. Video conversion is very processor-intensive, so a faster processor will help in this respect. If the video can be captured in MPEG-2 (for Super VCDs/DVDs) or MPEG-1 (for VCDs), then the conversion process can be eliminated. This will speed things up considerably.

    Also, because different software use different ways to convert video, some software will be faster than others.
    The speed of the DVD-RAM/RW writer will also matter, of course. Some DVD-RAM/RW writers have faster access times; some are capable of recording at higher transfer "speeds" (SMILY_.png as opposed to 4X, for instance).
    All these factors will have an impact on how fast the work gets done.

    Question : Sometimes, after I finish the job and play the VCD, I find that the quality is lacking - the picture breaks into little squares. Did I choose the wrong format?

    Answer : One problem with video is that if you pan (swing the camera from one side to another) too fast, the video may break into little squares. This happens because of the way the video is rendered.
    To save on bandwidth, many codecs use what is called "delta compression". This type of compression chops the image into small squares. The squares are independent of each other and can be updated independently of each other. This saves bandwidth because in any moving image, there are large parts of the image that don't move, or don't move all the time.

    For instance, if you take the standard "reporter at a crime scene" video, you can see that most of the time, the only things that move are parts of the reporter's face and maybe the cars on the road. A building behind the reporter, for instance, usually never moves. So, by dividing the screen into square sections and updating only the sections that change, a codec can save bandwidth.

    The main drawback with this approach is, if the whole screen suddenly moves all at once, all the sections will need to be constantly rendered and updated. If there isn't enough bandwidth to update the whole screen at once, the video will break into squares as different sections of the screen update at different times. To prevent this, avoid moving the camera too quickly. Increasing the bandwidth (for instance, by recording to DVD video instead of VCD) will also help.

    Another possible reason for "squares" on a video is the capture bit rate is set too low. The capture bit rate of a particular movie can usually be set on the capture device or camera.


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