You should use YouTube API v2.0 – Using Batch Processing.
You may post an XML like this:
<feed xmlns="http://www.w3.org/2005/Atom" xmlns:media="http://search.yahoo.com/mrss/" xmlns:batch="http://schemas.google.com/gdata/batch" xmlns:yt="http://gdata.youtube.com/schemas/2007">
<batch:operation type="query" />
<entry>
<id>http://gdata.youtube.com/feeds/api/videos/weRefE-qw9</id>
</entry>
<entry>
<id>http://gdata.youtube.com/feeds/api/videos/kkT-t894YSa</id>
</entry>
...
</feed>
To this URL:
http://gdata.youtube.com/feeds/api/videos/batch
This is a quote from documentation:
The YouTube Data API supports batch processing, enabling you to
execute up to 50 operations with a single API request rather than
submit a separate request for each individual operation. A batch
processing request can combine multiple query (GET), insert (POST),
update (PUT) and delete (DELETE) operations. Each operation is
contained within an <entry>
tag in the request. This section explains
how to format batch processing requests and handle the API responses
to those requests.