近年來市面上出現很多數位型態的多媒體產品，數位產品的特點就是攜帶方便、流通性強，但由於近年來網路技術進步很快，再加上數位儲存媒體日新月異，不僅攜帶更方便儲存容量也變更大，再加上網路頻寬也變大很多，使得數位產品的傳播性更強，也因此出現許多不法之徒利用不正當的行為，竊取他人所製作的數位產品的內容，所以許多電影業者和音樂製作者都遭受到巨大的損失。
而為了達到保護數位內容的目的，方法和手段其實有很多，我們可以在數位內容裡加入一些訊息或者是訊號，可以是一張數位內容製作者的影像，或者是一段宣示版權的文字內容，這些保護訊號在此我們通稱為浮水印技術( watermarking techniques )，浮水印的目的主要是要宣告版權所有，和有效嚇阻不法者對數位內容進行不法的行為，而一個好的浮水印技術則必須具備幾個特點：無法察覺性、強韌性、即時性的藏匿動作、不模稜兩可的、取出浮水印不需原始影像。
本篇論文中提出了一個以H.264為實驗標準的浮水印技術，所提出的浮水印技術具有很低的計算複雜度，所以可以即時的加入浮水印於影片中，本方法在取出浮水印時也不需要原始影片，對於被加入浮水印的影片而言，其影像品質不會毀損過多而能保持相當好的視覺效果，而且加入在影片中的浮水印能抵抗基本的重複壓縮攻擊；所提出的浮水印方法是將浮水印藏在適當的4x4編碼區塊中，我們會根據不同頻率所給於的權重值α、β、γ和自訂的門檻值T，以及一個切斷索引值c來挑選適當的編碼區塊，藉由移除編碼區塊中的DCT係數來修改編碼區塊，因此可以讓適當的編碼區塊可以符合浮水印藏匿的條件。

Key words: H.264, watermarking, weighting
A low complexity watermarking method in the compressed domain for H.264 is proposed. It embeds the watermark in a quantized 4x4 coding block. Because DC coefficient affects the quality of video very much, we just modify the remaining 15 AC coefficients for embedding the watermark. We divide the AC coefficients in the embeddable block into two groups. The coding block is embeddable if the watermark embedding function of the coefficients in these two groups is greater than a threshold. It is embeddable. The block is embedded with 1 or 0 according to the weighting functions of these two groups. The proposed method has higher capacity and could resist basic recompression attack by mean of comparing other algorithms. The experiment result shows the proposed method could maintain video quality.

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