Several types of objects are embedded in a post or a page via what WP calls shortcodes. Among others –
• Youtube shortcode:
• Vimeo shortcode:
|[vimeo NUMBER HERE]||or||[vimeo http://vimeo.com/NUMBER HERE]|
• Poll shortcode:
|[polldaddy poll=NUMBER HERE]|
• Audio player shortcode: 
|[audio URL HERE]||or||[audio=URL HERE]|
• Gallery shortcode: 
As the WP FAQ says (with some amount of bullshitting), the shortcode business means “you do nifty things with very little effort”: “just one line” instead of “lots of complicated, ugly code”. Unfortunately it also means that all or most parameters are rigidly predetermined and outside your control. Videos, for instance, are center aligned; polls, on the other hand, as well as the audio player, are left aligned; in all three cases, text or another object will follow below them. You cannot change any of that by using the alignment buttons of the editor.
You can do it, however, by enclosing the shortcode in suitable html codes (in the html post or page editor, of course):
Video left aligned (no text wrap)
Cazzati: Ciaconna. Ensemble L’Arpeggiata, dir. Christina Pluhar.
Video left aligned but indented
(The number is arbitrary – you can change it.)
Stravinksy: The Rite of Spring (ending). Wuppertal Dance Theater, chor. Pina Bausch.
Video left aligned, with wrap-around text
Bach: Es ist vollbracht, from the St-John Passion.
Panajotis Iconomou, boy alto.
Christophe Coin, viola da gamba.
Concentus Musicus Wien, dir. Nikolaus Harnoncourt.
“Es ist vollbracht.
O Trost für die gekränkten Seelen;
die Trauernacht läßt mich die letzte Stunde zählen.
Der Held aus Juda siegt mit Macht und schließt den Kampf.
Es ist vollbracht.”
[Translation:] It’s finished now. Oh consolation for the souls that suffer; this night of woe makes me the final hour ponder. The Judahn hero wins with might and ends the strife. It’s finished now.
[Cf John 19:30: “When Jesus therefore had received the vinegar, he said, It is finished: and he bowed his head, and gave up his spirit.”]
Series of left aligned videos, with text blocks next to each video
This way each video/text pair will be vertically centered; if you want their tops aligned, change each opening td tag to this:
Series of left aligned videos, with text running next to them
See this post, under “Two columns”.