Uploading and encoding of large video files already happens, Tangram is just the encoding service to make the compression and the conversion of these files faster and cheaper than traditional services (like Amazon AWS). Tangram is built to be compatible with cloud storage services like Amazon S3, to encode files in multiple profiles stored by video content providers without relying on large infrastructures or high costs.  
Also, Tangram splits the video files in chunks and the nodes of the network only encode little parts of the file. Tangram starts the transcoding process while the file is being uploaded on its network