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Design and Implementation of Software-Based MPEG-4 AVC/H.264 encoder on Multi-Core Processors
No full textMPEG-4 AVC/H.264 是現今最先進的影像編碼技術。相較於昔之技藝，MPEG-4 AVC/H.264可節省大約50%的儲存空間並且提供更優良的視覺效果。然而在達到更優秀壓縮效能的同時，MPEG-4 AVC/H.264需要更高的計算複雜度。根據運算時間的分析結果顯示:在高解析(High Definition)的影片中，移動估測(Motion Estimation)使用了超過百分之75以上的計算量。因此，在本論文中，我們探討如何降低移動估測中各個編碼工具(Coding Tools)的複雜度。在MPEG-4 AVC/H.264中，移動估測使用了相當多先進的編碼工具，包括多重參考畫面(Multiple Reference Frame)，可變動區塊大小(Variable Block Size)，以及1/4像素精準度的移動向量(1/4 pixel motion vector)。針對多重參考畫面，我們利用空間中相鄰畫面間的相關性設計出一快速演算法，可減低計算的複雜度並保留此編碼工具的優點。此外，針對其他編碼工具，我們探討並實做不同演算法來降低運算的複雜度，並藉以瞭解不同演算法在高解析度的影像下，壓縮效果的差異。藉由上述的方法，移動估測的計算複雜度下降至整體編碼時間的38%，而整體編碼時間則加速了14倍，此外這些的加速方法僅帶來些微的畫質衰退或壓縮比的降低。
隨著各種不同應用的需求，多核心的處理器架構逐漸被廣泛的採用。在嵌入式系統中，非對襯型處理器架構被用以來處理不同性質的工作; 而對襯型處理器則被視為下一代個人電腦的主流。然而，一般的影像編碼器僅為單執行緒，無法使用多核心處理器的優點，因此本論文著重於多核心影像壓縮技術的研發。傳統的多核心壓縮著重於同時處理不同的資料，譬如：Slice ;然而這種方式通常適用於對襯型處理器。為了適用於非對襯處理器，我們分析影像壓縮的流程，探索各項工作間的相關性而設計出一平行處理不同編碼工具的架構(Function parallel scheme)。此外，我們亦結合昔之同時處理不同資料的技術，提出一混合的架構(Hybrid parallel scheme)，可提高在對襯架構下的效能。我們所提出的兩種架構可提高MPEG-4 AVC/H.264在多核心架構下編碼的效能，並且不增加系統資源的使用量。The latest video coding standard, MPEG-4 AVC/H.264, achieves better coding performance than prior codec. As compared to MPEG-4, H.263, and MPEG-2, MPEG-4 AVC/H.264 saves about 37%, 48%, and 64% bit rate, respectively. However, the better performance is contributed by advanced coding tools which result in higher computation complexity. And the higher complexity limits the application scenarios. According to the time profiling analysis, temporal domain prediction takes about 75% execution time on HD resolution videos. Therefore, our work accelerates the temporal prediction via several efficient algorithms without serious side effects. First, we propose a fast algorithm for multiple reference frames based on correlations between temporal adjacent frames. In addition, several simplification methods for block-matching, variable block size motion search, and fractional pixel search are studied and implemented to reduce the required computation load. While those algorithms are applied, the temporal prediction requires only 38% of the computation load. Besides, as compared to the H.264/AVC reference software, our encoder achieves about 12X speed up without inducing serious quality degradation and compression ratio drop.
Nowadays, the multi-core processor architecture becomes more and more popular and is widely adopted in many areas. In the embedded systems, asymmetry multi-core processors are applied to complete tasks with different attributes while symmetry multi-core processors are considered the next generation of CPU on personal computers (PCs). However, the common H.264 encoders are single-threaded and can not take the advantage of multi-core processors and therefore, several parallel schemes have been proposed. The traditional methods aim to manipulate multiple data sets, such as slices, in parallel but are only applicable on symmetry architectures. In our work, we exploit the dependency relationship between coding tools and design a function parallel scheme for asymmetry architectures. Furthermore, we utilize a wave-front macroblock encoding order to avoid the inter-dependency between data sets and propose a hybrid parallel scheme applicable for both symmetry and asymmetry architectures. With the proposed schemes, the encoding process is further accelerated.1 Introduction : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 1
1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Encoder Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Software-based Encoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4 Multi-threaded Encoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.5 Thesis Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2 H.264/AVC Coding Tools Overview : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 9
2.1 Pro‾les and Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Temporal Domain Prediction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.1 Multiple Reference Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.2 Variable Block Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.3 Quarter-Pixel Displacement Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3 Spatial Domain Prediction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.4 Transform and Quantization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.5 Adaptive Deblocking Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.6 Entropy Coding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.6.1 Exponential-Golomb Entropy Coding . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.6.2 Context-based Adaptive Variable Length Coding . . . . . . . . . . . . . . . . . . . 23
2.6.3 Context-based Adaptive Binary Arithmetic Coding . . . . . . . . . . . . . . . . . 25
3 Temporal Domain Prediction : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 27
3.1 Motion Vector Search in a Single Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.2 Motion Vector Search in Multiple Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.2.1 Fast Multiple Reference Frame Search . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.2.2 Skippable Multiple Reference Frame Search . . . . . . . . . . . . . . . . . . . . . . 36
3.2.3 Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.3 Motion Vector Search for Variable Block Sizes . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.3.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.3.2 Top-Down Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.3.3 Bottom-Up Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3.3.4 Merge&Split Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
3.3.5 Motion Vector Re‾nement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.3.6 Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.4 Motion Vector Search for Fractional Pixel . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
3.4.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
3.4.2 Prediction-based Directional Fractional Pixel Search . . . . . . . . . . . . . . . . . 71
3.5 Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
The Value of Stop Loss Strategies：The Evidence from Taiwan Stock Market
No full text根據過去國內外的研究指出，停損策略可以避免投資人發生錯置效果，也就是急於賣出獲利的股票，卻捨不得賣出手中虧損的股票；然而，對投資人來說，最重要的仍是報酬率。因此，本研究欲探討的是停損策略是否能為投資人帶來較高的報酬率，或是減低少投資人的虧損。 與過去研究不同的是，本研究以2004-2014年台灣股票市場所有股票為樣本，並以每檔股票過去的報酬率標準差為基準設定停損點，以防止因波動性不同而造成跌至停損點難易度的不同，並且不設定任何買進訊號。除此之外，本研究以迴歸模型的方式，探討是否有股票特性能影響停損策略的有效性，最後檢定停損策略是否能降低投資風險。 研究結果顯示，停損策略不能為投資人提高報酬率，或是減少虧損，且無法由特定股票特性判斷停損策略的有效性；然而，停損策略可以顯著地為投資人降低投資風險，避免投資人承受一次性的巨大虧損。According to domestic and foreign researches, stop-loss strategies can prevent investors occurring disposition effect, that is holding their losing investments too long and selling the stocks which are winners early. However, the most important thing to investors is return. Therefore, this thesis examine whether stop-loss strategy can lead to higher return or reduce losses for investors. Different from the past research, this thesis uses all the stocks in Taiwan stock market from 2004 to 2014. To avoid the difference of volatility causes different degree of difficulties to reach the stop price, this thesis sets the stop price based on every stock’s daily return standard deviations. In order to prevent other factors making effects on the result, this thesis does not set any specific condition and signal to buy the stocks. In addition, this thesis uses regression to examine whether stock characteristics can affect the validity of stop-loss strategies. In the last we examine whether stop-loss strategy can reduce investment risk. The result shows that stop-loss strategies neither reduce the losses nor increase the return, and investors cannot judge the validity of stop-loss strategies by specific stock characteristic. However, stop-loss strategies are able to reduce investment risk for investors significantly, avoid investors having a huge loss in one investment
Motion Transitive Based Fast Multi-frame Motion Estimation Algorithm for MPEG-4 AVC/H.264
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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