在資訊傳遞的過程中；視覺訊號的傳遞不僅是較直接的方式同時也是一種較有效率的呈現方法，隨著無線網路機制的日益成長；可攜式無線影像播放器之需求必定成為未來消費市場的主流，例如剛推出的”影像手機”就是一個例子。

目前市面上有許多可以播放多媒體的產品；例如：PDA、Webpad與Tablet….但由於多功能的因素往往造成產品成本的提高，這樣的結果使得單一功能的產品較有競爭力。舉例來說：如果只想聆聽音樂；可以選擇MP3隨身聽即可；而不是高價位的PDA。基於這個理由，將如影隨行的產品定位在：一個具有高畫質、低成本的單一功能影音播放器。

“如影隨行”的基本理念是使用一片彩色TFT的LCD加上StrongARM處理器來完成，在無線傳輸方面則使用802.11b的無線區域網路技術來實現，將影音資料流藉由乙太網路傳送到Access Point，使得Server端的影像得以傳播到任何一組如影隨行播放器。利用這樣的機制；使用者可以用 ”走到哪show到哪”的方式來達到無線影像接收的目的，這也就是取名為”如影隨行”的主要原因。而數位化的便利性將使本系統具有:畫質優異、資料處理便利、無失真傳輸、提昇與數位系統整合性…等優勢。
由於使用作業系統是ARM Linux kernel；在作業系統核心、驅動程式、影音輸出函式庫、應用程式….等我們都提出精簡與移植的方法。而在StrongARM不支援浮點運算進而導致播放音質不佳的情況下；我們也提出了一套定點化的解決方案。

軟體開發過程中完全不採用商用的開發軟體，而使用網路上的open source免費軟體來完成，這樣的方式將使得軟體開發成本有效的降低。在模組化的設計下；未來如果有更好的通訊協定或是技術；只要使用替換模組的方式便可以提昇本系統的網路頻寬與影像畫質。

實驗結果方面，如影隨行的畫質比市面上iPAQ PDA更為流暢，在使用一台Access Point 情況下，同時間最多可播放四個不同的頻道。另外在應用上，我們也達到即時壓縮編解碼播放的功能；使得無線數位電視得以實現。

論文的實作中，我們研究並設計了一套具單一播放影音功能的軟硬體架構；同時達到低成本、高畫質的需求。在產品應用方面；如影隨行的應用範圍也相當廣泛，例如：資訊家電、影像保全系統、數位電視、無線影像公佈欄、動畫式廣告傳播、導覽系統….等

In the data transmission area, visual communication is not only a direct way but also an effective form of expression. With the continuing growth of wireless network, an embedded wireless multimedia player must be an important electronic device in the future market. For instance, we can use a mobile phone with image expression function.

There are several multimedia devices with the benefit of multifunction, for instance, PDA, Webpad and Tablet, etc., but the cost is higher than the device with single function. For example, if we just want music; we can choose an MP3 player instead of PDA. In this case, we proposed a specialized multimedia player with better image quality and high competition of price.

The basic idea of our “Inseparable Image” is to make a wireless multimedia player based on a TFT LCD and a StrongARM processor. In the aspect of wireless communication, the 802.11b is used as our Wireless LAN transmission protocol. The multimedia streams are transmitted from a server over the Ethernet to the Access Point, and every player can receive them under wireless environment. By means of this portability, users can receive the real-time data stream in everywhere they are, and it is why we call it “Inseparable Image”.

By using digital transmission, several benefits such as high quality, easy to store and compatible with other device, etc., are also obtained.

According to the ARM Linux kernel, the modifications of drivers, O.S., audio/video output library, drivers and application programs are proposed. As the StrongARM processor doesn’t provide the capability of floating-point computation, we also proposed a fix-point solution for it. Due to modularized designing style, the bandwidth and image quality supported by the proposed system can be easily upgraded by better wireless protocol or technology in the future.

We have done the experiment of multi channel playing mode, 4 players can work simultaneously with one access point and keep good image quality. In comparison with the iPAQ PDA, our system also has better performance. Besides, we also have the capability of real-time encoding and decoding.

In summary, we designed a low cost, high performance software and hardware structure focused on multimedia playing. Our system also has high flexibility to achieve various applications such as information appliance, secure system, digital TV, advertisement board, bulletin board, etc.

[1] VideoLAN www.videolan.org
[2] 台灣鉅格系統科技公司 www.mastia.com.tw
[3] ARM Linux on Assabet
http://www-2.cs.cmu.edu/~wearable/software/assabet.html
[4] Embedded Linux Survey, Copyright Blue Mug,
Inc. 2001, 2002 www.bluemug.com
[5] Linux iPAQ: Mobile Multimedia Platform http://internet2.motlabs.com/ipaq/#vic
[6] Qt / Embedded http://www.trolltech.com/
[7] GTK http://www.gtk.org/
[8] Serial Cable Connections for the H3600
http://handhelds.org/
[9] The Familiar Project
http://familiar.handhelds.org/
[10] SHARP’s SL-5000 http://more.sbc.co.jp/slj/hw.asp