To change and resize the width and height of the video we are going to display, we can add a function to the theme's function.php to do this for us.
I got this function from Vinod Kumar explained here:
Dynamically Change Width and Height in embed code

So put this function into your functions.php first:

// the function to resize oembed videos
function resizeMarkup($markup, $dimensions)
{
$w = $dimensions['width'];
$h = $dimensions['height'];

$patterns = array();
$replacements = array();
if( !empty($w) )
{
$patterns[] = '/width="([0-9]+)"/';
$patterns[] = '/width:([0-9]+)/';

$replacements[] = 'width="'.$w.'"';
$replacements[] = 'width:'.$w;
}

if( !empty($h) )
{
$patterns[] = '/height="([0-9]+)"/';
$patterns[] = '/height:([0-9]+)/';

$replacements[] = 'height="'.$h.'"';
$replacements[] = 'height:'.$h;
}

return preg_replace($patterns, $replacements, $markup);
}

Having this code activated by putting it in functions.php, we can use it as explained in Vinod's post (link above).

We want to use this function to change width and height attributes throughout the oembed code we retrieved before from the WordPress database.
As explained here: http://forum.go41.de/topic/get-the-oembed-code-of-a-video-in-a-wp-29-post-from-postmeta we have already a variable assigned to the oembed code, now we just pass this variable to the function 'resizeMarkup' with new values for width and height and echo the resized video clip.
To do this we put into the loop this code:

<?php if(function_exists('resizeMarkup')) {
	$resizedvideo = resizeMarkup(($embedhtml), array(
	'width'=>300,
	'height'=>250 ));
	echo $resizedvideo; } ?>

Any questions? Sign up and ask, you are welcome.

Working inside the loop, we are going to get the unique meta_key of a post starting with oembed. If in a post is this meta_key we assign this to a variable (here: $oembkey)
Next we get the value of this key, which is actually the full html embed code (here: $embedhtml)

Finally we can echo $embedhtml to display only the video without the_content or the_excerpt.

The code to get only the embeded video:

<?php
  $custom_field_keys = get_post_custom_keys();
  foreach ( $custom_field_keys as $key => $value ) {
    $valuet = trim(substr($value, 1, 4));
	if ( 'oemb' == $valuet ) { // look if a oembed key exists
    $oembkey = $value; //now set the the key we found as oembkey
	$oembvalue = get_post_custom_values($oembkey); //get the value of oembkey as oembvalue
	if (isset($oembvalue[0])) {
		$embedhtml = ($oembvalue[0]);
	  }
	}
  }
?>

and now echo it:

<?php echo $embedhtml; ?>

In another topic I will explain how to resize this player here:
Change width and height in oembed code on the fly WP 2.9