Final Project Report Customized and manageable streaming service using a file-converting server

Transcription

1 Final Project Report Customized and manageable streaming service using a file-converting server Seunghoon Jeong {sejeong@cs.ucsd.edu} November 30, 2006 Abstract Thanks to enhanced codec technology and powerful processing ability of CPU, large-sized and highquality multimedia files are increasing. Even though recent PCs can play highly compressed video files without any loss of quality, those files are inadequate to be played in cell phones or PDAs. Even the most recent cell phones have processing powers of PC several years ago and they do not have a sufficient amount of storage to save them. The streaming service can be a good solution to resolve the problem. However, present streaming services are only for their subscribed customers and the content scale is incomparable to the one available for PC: the Internet content. Furthermore, the present streaming services do not support enough dynamic controls over the stream, which are natural in non-streaming format files. In this project, I designed and implemented a model that enables cell-phones to play and control video files formatted for PC by customizing and streaming them using a file-converting server. 1 Introduction It is now common that we can see TV programs and movies with a cell phone. Increasing number of them are now equipped with web-accessible ability. Processing ability of recent cell phones is now similar to that of PC several years ago and they can play multimedia files through web access. It is a big merit that mobile cell phone can play multimedia files made for PC. However, the problem is that plenty of the files are not directly usable for cell phones. Large-sized non-stream format files are difficult to be played in cell phones with limited storage. Even though recent cell phones contain large storage than old ones, video file size is also increasing beyond the capacity of cell phones.in addition, even if cell phones have enough storage to save large video files, they still have the limited resource environment: low processing ability and small view size. Since most recent video files are formatted by advanced codec with wide view size configuration, cell phones are unable to play the quality that is expected to be shown. Playing high-quality video files for PC in the low-quality environment of a cell phone is inefficient and resource-wasteful. Streaming service can be the solution of the two problems. However, present streaming services also have limits. Most of them are for subscribed customers and contents are limited. Moreover, they support little dynamic controls over the stream, which are very natural for non-stream format files. In cell phones dynamic control functions are more important due to their resource and power constrains than those of PCs. Since computer performance and network speed has greatly enhanced, we can utilize a third party file-converting server for customized and manageable streaming services for cell phones 2 Related Works For better streaming service, a lot of works have been done across various research areas. In streaming codec aspects, ASX, ASF, WMA and WMV, which were proposed by Microsoft, are widely used. Several Internet Protocols for streaming services have been suggested and adopted [1] [2]. A typical streaming protocol is the Real Time Streaming Protocol, RTSP, which is an application-level protocol for control over the delivery for data with real-time properties. Some researches related to system designing introduce new methods for 1

2 Figure 1: scheme scenario better performance in streaming services [3], [4]. QoS is one big issue in streaming service. Some researches like [5] are about estimating streaming quality. The topic of the customized streaming service has been more prevalent in commercial services rather than research area. Most major TV broadcasters such as CNN and NBC now provide their TV materials, but majority of them are aimed for PC users accessible to the Internet. Last year South Korea started to provide the satellite Digital Multimedia Broadcasting service, which is a big advance in mobile streaming service. However, present mobile streaming services are restricted only to certain models and their content is very limited. There have been little attempts to utilize a third party server to customize Internet video files for heterogeneous cell phones with dynamic controls. 3 Goals The project was performed to achieve the following goals assuming that PXA27x behaves as a cell phone. 1. Since cell phones do not have sufficient storage to save large-sized non-stream format video files, URLs of the video files are redirected to a third-party server and cell phones get streaming services from the server. 2. Since plenty of video files in the Internet are formatted for PCs and each cell phone has different capability, the server customizes the streaming file through optimizing process; it prevents waste of resources in cell phones to play streaming videos. 3. By making the client and the server have seeking functionality of a streaming data, cell phones can control the stream dynamically. Figure 1 shows an imaginable scenario. First, a cell phone obtains a URL of a video file from the Internet. Then, the client in the cell phone redirects the URL with its running information such as the screen size and the CPU speed to the server. Next, the server downloads the requested file and converts it with the optimizing process. During the process, non-stream format is converted to streaming format and the video file is optimized to the cell phone Finally, the server starts a manageable streaming service to the cell phone; the client may send dynamic control requests such as FF/REW and the server responds to the corresponding commands. 2

3 Figure 2: System Model Figure 3: User Menu Tree 4 Design and Implementation 4.1 Client Figure 2 shows the communication model between the client and the server.the client contains three modules: user command processing module, mplayer wrapping module, mplayer and communication module. 1. User command processing module: this module shows a tree-like menu as shown in Figure 3. It gets input and applies the corresponding commands. File control menu is for commands to request an Internet video file and a streaming service to the server. View control menu is for commands to dynamically control streaming video streams: PAUSE, FF/REW, SEARCH, RESIZE. At first, this module was designed to read a XML file, which contains a command list with corresponding execution information, and to automatically build the command tree for extensibility. However, since some XML libraries were not supported by arm-linux, XML-based input module could not be implemented. 2. Mplayer wrapping module: The client includes an mplayer wrapping module, with which the client operates as a frontend of mplayer executing mplayer as a slave mode. When run with slave mode, mplayer will read primitive commands from stdin and returns the results to stdout. Since the client need to communicate directly with mplayer between the user and mplayer, the client wrapping module forks mplayer program and communicates with it through a pipe line, through which control primitives are delivered and mplayer applies the commands. 3. mplayer: To enable a dynamic control of FF/REW in mplayer, I intended to add to mplayer source code a functionality requesting a streaming data of a certain position and make a streaming server facilitate the requests. After analyzing the mplayer source code I found that mplayer has a minimal support for the dynamic control over streaming video and I used the mechanism with some modifications to compile. Figure 4 shows the streaming protocol and how FF/REW dynamic control mechanism is performed based on the streaming protocol. In dynamic control over streams, some commands like 3

4 (a) streaming protocol (b) a streaming control process Figure 4: Dynamic controlling PAUSE and FF/REW are implemented directly with supported primitive commands: pause and seek. However, a RESIZE control function could not be applied directly to the running stream. For that object, several consecutive phases were used: saving the stream position, rerunning mplayer with specified view size and relocating the position. 4. Communication module: the communication module is the interface to communicate with a server. It may request to retrieve a playable file list, add a video file with URL, and start a streaming service for an available streaming file. The communication was implemented on TCP/IP socket programming, and several protocol type and data structure were defined for the communication. 4.2 Server Server consists of three modules: a communication module, a downloading and converting module, a streaming module. The communication module permits multiple connections from clients. It accepts a connection from a client and delivers request commands to the corresponding module. The downloading and converting module uses wget and ffmpeg internally for downloading and coverting process. For a requested URL of video file from the client, this module executes downloading and converts the saved file into streaming format for the client with optimizing process. When the server is ready to start streaming service, the module notifies the client and the streaming module does streaming service for the client. To facilitate the dynamic control requests from the client, mplayer/libmpdemux/netstream and mplayer/tools/netstream source code were analyzed and used with some modification 5 Conclusion By designing and implementing the model, I could verify several benefits what I expected. First, using a third party server, the client could play a large sized non-stream video file in the Internet without using NFS and without client s need to save files, which is the actual scenario of the most cell phones. Second, during the testing process, I could see waiting time for a client to play a movie file is greatly reduced without loss of video quality. Thanks to the stable and fast wired network speed of the server, downloading time was greatly shortened and the conversion process reduced the saved file size below one fifth of the original 4

5 one thanks to optimizing process. It is required to prevent resource waste in cell phones. Finally, dynamic control over the streaming was enabled with the support of streaming server, which is necessary function for the resource-constrained cell phones. 6 References 1. RFC RFC F Yu, Q Zhang, W Zhu, YQ Zhang, QoS-adaptive proxy caching for multimedia streaming over the Internet, Circuits and Systems for Video Technology, IEEE Transactions, ieeexplore.ieee.org 4. H Zheng, Optimizing wireless multimedia transmissions through cross layer design, Multimedia and Expo, ICME 03. Proceedings. 2003, ieeexplore.ieee.org 5. M Ries, R Puglia, T Tebaldi, O Nemethova, M Rupp, Audiovisual Quality Estimation for Mobile Streaming Services, Wireless Communication Systems, nd International, ieeexplore.ieee.org 6. YF Chen, H Huang, R Jana, S John, S Jora, A, Personalized multimedia services using a mobile service platform, Wireless Communications and Networking Conference, 2002., ieeexplore.ieee.org 7. SI Kang, J Song, SK Bae, HK Lee, Access emulation and buffering techniques for streaming of nonstream format video files, Consumer Electronics, IEEE Transactions on, ieeexplore.ieee.org 5