Mobile Video Testing

Mobile Video is Reality

Mobile video covers the realm of both creating and forwarding video clips as well as watching content created by others. There are two types of mobile video content services: downloadable and streaming. Video clips can be downloaded, stored, and played back on mobile devices. Or data can be retrieved in the form of stream video content, which is a better option for viewing longer clips because data isn't stored on phone. User also have the option to tune in to live video feeds using streaming.

Operators being challenged on image clarity are looking at test systems that can accurately simulate video quality as perceived by subscribers. The following condensed essay provides an introduction to mobile video applications along with quality measurement considerations and solutions.  For a full treatise on video testing an Ascom white paper can be downloaded.

Common Mobile Video Uses

• Phones equipped with a camera can record clips which can be send to others by email, Video MMS, or over a wireless connection using Bluetooth technology or infrared
• Watching streamed news, sports, music videos, and movie trailers
• Watching live camera views such as road conditions, concerts, parties, etc.
• To access MMS video subscription services such as daily news, weather, or cartoons
• To store favorite videos on a Multimedia memory cards
• Mobile telephony allows the two parties to see each other during their conversation

How It Works

Unless the desired video is already stored on a mobile memory card (MMC), the phone must be able to connect to the Internet in order to access video files. This means a phone with a GPRS, EDGE, WCDMA or other network connection; Streaming video requires a phone that supports EDGE or WCDMA. Video Telepony is a person-to-person service supported in 3G networks.

Overview of Mobile Video Applications

Video MMS

MMS is a store and forward service using the MMS-Server as an intermediate storage element between two end-users. Associated with the MMS-Server is the MMS-proxy relay, which is responsible among other things for converting (adapting) messages to the capabilities of the receiving device. For instance, if a terminal sends a high-resolution color image to an older MMS mobile phone, the MMS proxy will convert the picture to black and white and adapt the resolution. Sometimes this transformation is not correct. This can occur, for example, if there are incorrect configuration settings in the MMS user database. In this case, the result of the picture can be completely different from the original. Errors like these are independent of the quality of the transmission path and can be easily detected by stationary tests between specific mobile phones over the MMS-server of interest.

Video Download

Video Download refers to the delivery of video clips to a mobile phone. After discovering clips of interest during browsing, a user can initiate a TCP/IP session where the video clip is sent to the handset and where it can then be viewed or stored.

The TCP/IP protocol insures correct transmission of the content. As long as the player buffer in the mobile phone or in the PDA is not emptied, the video clip content will be exactly the same as the original one on the media server. The price for this excellent video quality is download time.

Video Streaming

Video Streaming is a method for transferring moving pictures in such a way that the recipient can start viewing the material before the entire content has been transmitted. Data transmission rates of GPRS and WCDMA make streaming of audio and video a reality in mobile networks.

The same video content can be downloaded or streamed. As described above, downloading will give a perfect reproduction but it takes time and requires storage capacity. Real streaming, alternatively, needs minimum network bandwidth.

Video Telephony

Video Telephony is a full-duplex/real-time audio-visual communication between or among end users. Video telephony connects people face-to-face, over any distance. In this age of Email, instant text messaging, Video Telephony brings the personal nuances that only come from face-to-face communications. Inflections, expressions, and other non-verbal cues that are lost in cyberspace will be preserved with video telephony.

QVoice Perceptual Quality Measurements Explained

All mobile video services are vulnerable to transmissions errors that can be distracting and unpleasant to subscribers. Accurate measurement and assessment of these perturbations are realized in QVoice using absolute perceptual metrics algorithms that take into account the image content and frame data of the video resulting from the given coding and transmission conditions.

Absolute metrics is ideally suited for in-service quality measurement of video streaming which allows real-time testing of quality at any point in the content reproduction and delivery chain. Absolute metrics are particularly useful for monitoring quality variations due to network problems.

The most common artifacts in video (described below) as perceived by a human viewer are easily recognized even by inexperienced people. QVoice absolute metrics simulates these artifacts and provides an automatic measure that correlates with human perception.

Jerkiness

Jerkiness is perceptual measure of frozen pictures or motion that does not look smooth. Transmission problems such as network congestion or packet loss are the primary causes. Because video transmission is a time-critical process, missing data packets cannot simply be retransmitted. If substantial parts of the video stream are not available when they are needed for display, decoders often show the last good picture until they can resume play back.

Blockiness

Blockiness is a perceptual measure of the block structure common to all DCT-based image and video compression techniques. DCT, usually performed on 8X8 blocks in the frame, are quantized separately, leading to discontinuities at the boundaries of adjacent blocks giving a blockiness effect to the image sequenced.

Blur

Blur is a perceptual measure of the loss of fine detail and the smearing of edges in the video. It is due to the attenuation of high frequencies by course quantization which is applied in every lossy compression scheme. It can be aggravated by de-blocking filters or low-pass filtering such as that used in digital-to-analogue conversion.