Videos that you upload to Yammer might not be available to play for a few moments after you upload them. That's because uploading the video into Yammer, and encoding the video so that it can play on Yammer, are separate processes. Encoding doesn't begin until uploading is complete, and the video can't play on Yammer until it's done encoding.
Whether the video is attached in a message or uploaded into the Files tab, it's available only as a downloadable file while it's encoding. Once encoding is finished, the video then is also available to play within Yammer. Unless the video is a very large file (remember the maximum upload size Yammer allows is 100 MB on free networks and 5 GB on premium networks), encoding should only take a few minutes.
Tip: Encoding happens in the background, so you can post the message or do other work while the video encodes.
Yammer encodes a video only once. For example, if you attach a video from the Files tab to a message, it doesn't need to encode again, and is available to view in Yammer immediately.