MediaShout does not have a firm rule as to what the "maximum" file size is for video playback.  However, it probably (partially) depends on how much RAM you have in your computer.  However, if the file is over 500 MegaBytes (MB) it's probably too large to play effectively.  Most likely, you're not compressing the video but rather trying to play the video full screen, uncompressed.

Try rendering the video using different video compression formats.  Our rule of thumb is that any format that is supported by Windows Media Player will play in MediaShout.  So, for example, if you want to use Divx, (which we would recommend for quality v/s compression ratio), you would need a Divx video decoder.  The best web site for this codec is Divx.com.