As I learned by trial and error, and as Keith from the Yammer team confirmed in the comments on Yammer 201, there is a limit on the file sizes you can share through Yammer: 20 MB. I had tried a 35 MB file, but that was rejected as being too large.
But there doesn’t seem to be a file type limitation. I did a 1:25 video yammercast (17 MB) yesterday and it worked well. I interviewed myself via Flip and then sent the QuickTime file via Yammer to one of my work teams.
It did take them a couple of minutes to download, so when you yammercast a larger file you may want to be sure to include some significant text in the Yammer post, so that in case the recipients don’t download the video they would still get the main point of the communication.
Keith included a helpful link to the Yammer blog that gives more detail on the file-sharing feature.
Yammer has built a lean, efficient platform for sharing. I like how photos that can be suitably displayed through the Yammer interface are embedded in posts, but larger, more complicated audio and video files can just be downloaded to be seen or heard in QuickTime or Windows Media Player.
If you want to share video with the world, YouTube is your great choice. But if you want to confine the distribution to your company, or to a work group within your company, try a yammercast.