Video Codecs

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How-tos


General

Video is increasingly used in professional event planning and in theatre as a medium for information and design. This is due in part to improved processing, and ever cheaper and more powerful output devices such as video projectors and LED matrices. From a technical point of view, when being played back a video signal must always be compressed; otherwise the data rate (bandwidth) would be too high.

A so-called video stream goes through a number of stages before it is viewed on an output device. Firstly, the data must be read from the hard disk or DVD, then copied into memory, and then unpacked by the CPU (Central Processing Unit), before an unpacked stream is sent to the graphics card, where it perhaps undergoes further processing. Only then can the signal be sent to the projectors. Naturally, each of these stages must have the corresponding capacity to be able to play back the video stream at the highest possible quality.

This is where the so-called codecs come in. Some codecs (e.g. DV) involve less compression than other codecs (e.g. H264), but require more hard disk space and a faster hard drive for playback, and thus higher bandwidth. Conversely, DV requires relatively little CPU computing time in comparison to highly compressed formats.

The rule of thumb: more compression = more demand on the CPU = lower bandwidth


MXWendler Recommendations

For smooth video playback, you can use eg.

  • XGA Size ( 1024x768 )
    • PhotoJPEG, 75% and ALAC Audio
  • HD Size and beyond
    • MPEG2 Video and MPEG3 Audio
    • h264 Video and ALAC Audio
  • Looping footage
    • Intra-Frame codecs like eg. Cinepak

Framerates

Whenever framerates do not match, video playback becomes jerky and stuttering. The framerates we are talking about here are

    • Video framerate
    • MXWendler framerate
    • Monitor framerate

Unfortunately today the most video output devices like monitors and video beamers have a 60Hz refresh rate following the tradition of the NTSC standard. Europeans are used to 50Hz PAL framerate, so most of the video material is produced in 25 FPS ( frames per second ). This produces the following situation:

    • 25Hz Video
    • 25Hz MXWendler
    • 60Hz Monitor

Since monitor and MXWendler does not match, the monitor has to show every 5th image twice, which will look unfluent. A better solution would be

  • Switch monitor to 75Hz framerate
    • 25Hz Video
    • 25Hz MXWendler
    • 75Hz Monitor
  • Switch video production to 30Hz framerate
    • 30Hz Video
    • 30Hz MXWendler
    • 60Hz Monitor
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