In this instance, the video file is downloaded to the handset completely before the handset starts playing it. Since the video is played when fully received on the handset, an ad server cannot detect whether the video content and ads are actually watched in their entirety. Due to the nature of the underlying technologies used, the quality of the received video files is as good as the quality of the source file on the network servers. Since the video files are stored complete on the mobile handset, copyright concerns are more apparent here. The most popular underlying technology is OMA download.