| 摘要: | H.264 在各式各樣的應用上皆可達到前所未有的壓縮效率，例如廣播、DVD、視訊會議、隨選視訊、串流播放，以及多媒體傳訊。而且在其先進的設計下，H.264 可在各式各樣的作業範圍內提供絕佳的畫質，包括3G 至 HD 等等。無論是行動電話、iChat、Internet、廣播或衛星播送，只要您需要高品質視訊，H.264 皆可利用超低資料傳輸率，產生卓越效能。
H.264因為擁有超低資料傳輸率，很適合應用於遠端傳輸，我們希望能夠架設一個當我們出差到國外時，也可以看到家鄉各種節目的平台，但最常發生的問題就是網路頻寬不足或是受到干擾的現象，所以我們提出了一種Auto bit-rate的方法，來降低當頻寬不足或是網路不穩定時，仍舊能夠收看穩定得影音品質，雖然要犧牲掉解析度，但穩定的影音品質會比失真率來的更好，我們之所以提出此種架構是因為，便利那些不懂得調整影音畫質的人，讓系統可以自動的調整最穩定的品質和當時網路可以傳輸的最高解析度。
為了驗證Auto bit-rate可行性,所以使用的測試平台為嵌入式平台，本文使用平台MCU為STR9105內建MAC及USB，執行速率方面約為200MHz，另外加H.264媒體處理晶片Ｍobilygen MG1264，是一個適合用在H2.64編碼與解碼的IC，由MG1264將影音訊號編碼成H2.64再由MCU透過MAC傳出網路封包，所以必須另外架設一台PC來做接收播放來做確認影像是否有即時與影像是否有延遲。
透過實驗平台，模擬各種實際網路可能發生的因素，並調整RTCP偵測時間的長短與計算bit-rate的大小，我們發現，在一定的頻寬下，若bit-rate調整的太小，雖然可以播放的順暢度變好，但是在播放影片時，播放的品質不好，解析度變差，若bit-rate太大，雖然影像品質變好，但所造成的影像延遲會無法即時順暢播放等等缺點，因此現實的網路系統中，因為環境並不是像網內頻寬這麼好，所以模擬實際環境與自動調整bit-rate是目前最重要的課題，我們將可以了解，該如何去設置bit-rate的大小，不但可以讓H.264播放的更順暢，也可以進一部的達到管理順暢度與解析度的目的。
H.264 format is a compressed technique that matchs to all kind of applicated terms.Such as broadcast、 DVD、media-meeting、VOD ( Video on Demand ) 、media-stream and multimedia ,In advance ,H.264 technique is able to offer the excellent picture quality in every kind of applicated condition including mobile phone、iChat、 Internet、boardcast and transmission of satellites. H.264 technique works excellently as providing high picture quality by low ratio data-rate.
Because the characters of H.264 technique form as low ratio data-rate transmited, it is very suitable to apply the remote transmission .Hopefullly , we wish to be able to wath all domestic TV-programs by installing some platform when being far away outdoor even oversea.It always happens to lack enough bandwidth or get worst signal , thus the Auto bit-rate technique improves the above two points; Althouh it may loss fine dpi , the stable AV quality is still worth overall.That is why we promote the Auto bit-rate technique with more convenience for tuning the optimal configuration in system.
We monitor all kinds of situation by experiment ; meantime , with tuning the timing RTCP detect and computing bit-rate . After all , it goes smoothly with lower bit-rate under limited bandwidth ,but the picture quality isn’t fine enough . As oppositely speaking , the picture quality is better with larger bit-rate; meantime , it also impact the system such as the whole loading and etc.Therefore , in the real network system ,with the limited bandwidth , it is not overemphasized to make the whole system optimal automatically as Auto bit-rate.We also realize how to configure the size of bit-rate ; not only for making the H.264 format more smoother , but for realizing the capacity of unhindered and the optimal managerment in advance. |
