What effect does the media type string inserted in a gstreamer pipeline have

[manickam palaniappan]

Hi,

Iam quite a newbie to gstreamer. Could somebody pls answer my below queries:
I have seen this kind of pipeline-running commands in gstreamer:

e.g.,gst-launch-1.0 videotestsrc ! video/x-raw, format=I420, framerate=25/1, width=640, height=360 ! xvimagesink
And I have read in some pages that "video/x-raw, format=I420, framerate=25/1, width=640, height=360 " specifies the media-type. But Iam not able to understand what effect would it make - is it transforming the input to the specified framerate/format/width/height etc.. or is it just like specifying the input is in this framerate/width/ht already ? and What effect it would have on the pipeline if it is just specifying the input is in this framerate etc... instead of transforming.
And is it really necessary or we can ignore it ?
Thanks,
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