We can easily add videos on our posts by using blogger post editing tool bar but by default blogger post's video size is small and doesn't fill the whole post width
The small size can affect your video impact on readers.
You can follow the following steps to increase the size:
1- Login to your blogger account
> Dashboard > Template > Edit HTML
2- find the line (by pressing ctrl+f )
</head>
3- add the following script before it:
<script src='//ajax.googleapis.com/ajax/libs/jquery/2.0.3/jquery.min.js' type='text/javascript'/>
<script>
$('.YOUTUBE-iframe-video').ready(function(){
$('.YOUTUBE-iframe-video').parent().css({
'position': 'relative',
'padding-bottom': '56.25%',
'height': '0',
'clear': 'both',
'text-align': 'center',
'margin': '20px 0'
});
$('.YOUTUBE-iframe-video').css({
'position': 'absolute',
'top': '0',
'left': '0',
'width': '100%',
'height': '100%',
});
});
</script>