• How to reduce the frame rate in a transcoded stream (SkipFrameCount)

    Wowza Transcoder always provides transcoded streams that use the same frame rate as the original video source. Some clients may not be able play streams with high frame rates. For example, you have a video source with a high frame rate, say from an HD video source encoded at 60 frames per second (fps) and you want to restream to devices that can't play at more than 30 fps. You must reduce the frame rate of the transcoded output stream(s) to support these devices.

    To reduce the frame rate of the transcoded output stream(s), add a SkipFrameCount XML tag to the <Encode>/<Video> section in your transcoder XML template. The SkipFrameCount XML tag must be positioned below the <KeyFrameInterval> block as shown in the following example:
    <KeyFrameInterval>
    	<FollowSource>false</FollowSource>
    	<Interval>60</Interval>
    </KeyFrameInterval>
    <SkipFrameCount>1</SkipFrameCount>
    The SkipFrameCount XML tag cuts the frame rate by using the following formula:

    Encoded frame rate/([SkipFrameCount value] + 1)

    So for example, a SkipFrameCount value of 1 cuts the frame rate in half, a value of 2 by a third, and so on. In the HD video source example discussed above, where the input source is 60 fps, a SkipFrameCount value of 1 reduces the transcoded stream frame rate to 30 fps. A SkipFrameCount value of 2 reduces the transcoded stream frame rate to 20 fps. The transcoded output rendition can then be played on many devices that have lower frame rate playback capability.

    Originally Published: For Wowza Streaming Engine on 08-19-2013.

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