A Modified H.264 Encoder to Stream Video for Narrowband Networks

隨著公共跟家庭安全日益重要，為了安全的考量，在一個監視系統內，盡可能有越多的監視器監看特定的區域越好，但由於經濟上的考量，通常不會有足夠的頻寬可以傳送所有監視器影像，尤其在窄頻網路中更是如此。了處理這個問題，我們提出了一個解決方法：一個改良型的H.264編碼器，它可讓使用者用很少的頻寬去盡可能傳送更多的串流影像。改良型編碼器主要想法就是把所有影像縮小並集中在一個影像後傳送出去。因為我們只是要從監視器內知道特定環境內發生了什麼事，對於傳送過來的影像是不是高畫質並不重要，只要還看得清楚就好，所以傳送過來的影像應該是要小而不是要求高畫質。在畫質仍然夠清晰，不影響觀看流暢度前提之下，把這四個從網路監視器傳送的影像輸入到系統，先把每一個都縮小，然後組合起來成一個較大的影像後傳送出去，如此一來減少監控時傳輸畫面的頻寬需求，同時也在可忍受的失真範圍內。考慮到每一個影像的畫面速率都不一定相同，不可能在每段時間裡所有的區域都有畫面可以取得，我們再針對有些區域沒有取樣時加以處理，加快壓縮速度。最後，將組合後的影像用改良後的H.264編碼器壓縮，然後透過網路傳送出去。評估系統時，我們比較了沒有經過縮小跟組合的傳統網路攝影機跟透過系統壓縮後所需的頻寬，以及比較原始的跟改良型H.264編碼器的編碼速度。經由效能評估，可以證實我們提出的改良型H.264編碼器，可以在有限的硬體花費之下，在傳輸頻寬跟壓縮時間上擁有較傑出的效能。Public and home safeties are important in human life. For the sake of security, it is necessary to have as many monitors of the surveillance system as possible to monitor specific regions. However, there is usually not sufficient bandwidth of networks to return all video streams, especially in narrowband networks.o solve this issue, we propose a modified H.264 encoder, which uses little bandwidth to transfer more video streams as possible. The key concept is to compress all input video streams into one. Because we just know what happens in specific regions, it is not imperative to store high-quality video. The video should be small size instead of precise. We shrink four observed videos to one-quarter and combine them into one as long as the quality is distinct and smooth enough. This way, it is able to reduce the needed bandwidth and have acceptable quality. Still, each video has different frame rate, it is impossible to get samples in all regions when sampling. We modify the original encoder to improve encoding time when some regions get no sample. Finally, we encode the combined image by using modified H.264 encoder.or evaluations, we compare the needed bandwidth of output generated by our system with that of traditional IP camera which is no scaling and combining on the input files, and the encoding time of modified encoder with that of original encoder. As confirmed by performance evaluations, the proposed modified H.264 encoder with limited hardware cost can achieve excellent performance in term of the bandwidth of transmissions and encoding time.口試委員審定書 i謝 ii要 iiiBSTRACT iv目錄 vi目錄 viiHAPTER 1. 緒論 1.1. 背景 1.1.1. 監視系統 1.1.2. 視頻編碼標準 2.2. 動機 4.3. 章節介紹 6HAPTER 2. 相關工作 8.1. H.264 8.2. FFMPEG 12.3. X264 13HAPTER 3. 系統設計與實作 15.1. 系統架構 15.2. 實作功能 18.2.1. Video Sampling 18.2.2. Video Scaling and Video Combining 19.2.3. Video Encoder 20HAPTER 4. 效能評估 25.1. 測試環境及方法 25.2. 測試結果與說明 26HAPTER 5. 結論與未來工作 29.1. 結論 29.2. 未來工作 30考文獻 3