# Frame-Based and Subpicture-Based Parallelization Approaches of the HEVC Video Encoder
## 4 Results and Discussion
### Subpicture Parallel Algorithms Analysis
\begin{table}
\begin{tabular}{l c c c c c c} \hline \hline  & \multicolumn{3}{c}{**QP = 37**} & \multicolumn{3}{c}{**QP = 22**} \\ \hline  & **Y-PSNR** & **Bitrate** & **Bitrate** & **Y-PSNR** & **Bitrate** & **Bitrate** \\ \hline
**NP** & **(dB)** & **(kbps)** & **Increment** & **(dB)** & **(kbps)** & **Increment** \\ \hline  & & \multicolumn{3}{c}{**Traffic**} & \\ \hline
1P & 34.0490 & 18,438 & & 43.2888 & 101,513 & \\
2P & 34.0469 & 18,464 & 0.14\% & 43.2883 & 101,559 & 0.05\% \\
4P & 34.0428 & 18,520 & 0.45\% & 43.2873 & 101,680 & 0.16\% \\
6P & 34.0385 & 18,560 & 0.66\% & 43.2849 & 101,748 & 0.23\% \\
8P & 34.0336 & 18,627 & 1.02\% & 43.2845 & 101,902 & 0.38\% \\
9P & 34.0319 & 18,658 & 1.19\% & 43.2837 & 101,980 & 0.46\% \\
10P & 34.0293 & 18,669 & 1.25\% & 43.2815 & 101,984 & 0.46\% \\ \hline  & & \multicolumn{3}{c}{**ParkScene**} & \\ \hline
1P & 32.7629 & 7271 & & 41.6499 & 52,608 & \\
2P & 32.7617 & 7291 & 0.27\% & 41.6496 & 52,647 & 0.07\% \\
4P & 32.7551 & 7319 & 0.66\% & 41.6485 & 52,710 & 0.19\% \\
6P & 32.7514 & 7354 & 1.14\% & 41.6473 & 52,766 & 0.30\% \\
8P & 32.7470 & 7388 & 1.61\% & 41.6463 & 52,843 & 0.45\% \\
9P & 32.7430 & 7397 & 1.73\% & 41.6451 & 52,858 & 0.47\% \\
10P & 32.7399 & 7413 & 1.95\% & 41.6446 & 52,897 & 0.55\% \\ \hline  & & \multicolumn{3}{c}{**FourPeople**} & \\ \hline
1P & 35.1856 & 6866 & & 43.7515 & 30,072 & \\
2P & 35.1721 & 6920 & 0.77\% & 43.7487 & 30,190 & 0.39\% \\
4P & 35.1617 & 7010 & 2.09\% & 43.7465 & 30,371 & 0.99\% \\
6P & 35.1503 & 7089 & 3.25\% & 43.7425 & 30,538 & 1.55\% \\
8P & 35.1298 & 7182 & 4.60\% & 43.7408 & 30,750 & 2.25\% \\
9P & 35.1336 & 7272 & 5.90\% & 43.7366 & 30,882 & 2.69\% \\
10P & 35.1190 & 7316 & 6.55\% & 43.7354 & 30,980 & 3.02\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Coding performance of the slice-based parallel algorithm. \begin{table}
\begin{tabular}{l c c c c} \hline \hline  & \multicolumn{3}{c}{**Speed-Up (QPs)**} \\ \hline
**NP** & **QP = 37** & **QP = 32** & **QP = 27** & **QP = 22** \\ \hline  & \multicolumn{3}{c}{**PartyScene**} \\ \hline
2P & 1.90 & 1.92 & 1.92 & 1.91 \\
4P & 3.49 & 3.46 & 3.54 & 3.61 \\
6P & 4.91 & 5.00 & 5.02 & 5.12 \\
8P & 6.90 & 6.80 & 6.88 & 7.04 \\
9P & 7.49 & 7.30 & 7.43 & 7.55 \\
10P & 7.98 & 7.97 & 8.04 & 8.24 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._Now, we analyze the performance of the tile-based parallel algorithm in order to see how the tile partitioning affects both the speed-up and the coding efficiency. First of all, we will analytically study the influence of the frame partition into tiles, i.e., how the nature of the video data may affect the algorithm performance. As stated in Section 2, we have selected the most homogeneous tile partitions for each number of processes that we have tested (2, 4, 6, 8, 9, and 10). In Table 4, we show the tile partitions (layouts) used for the 4 different video resolutions tested (\(2560\times 1600\), \(1920\times 1080\), \(1280\times 720\), \(832\times 480\)). The _AvgCTU_ column indicates the average number of CTUs per tile. For the 1P layout, this column indicates the total number of CTUs per frame. The _M_axCTU column shows the number of CTUs of the biggest tile for every layout. With the values of these two columns, we can obtain the percentage of workload balance (Bal %) of each partition. A load balance percentage of 100% indicates that all the tiles of one frame have the same number of CTUs, so the workload is perfectly balanced for all processes. Low values in this column (e.g., in the \(1\times 10\) layout for \(1280\times 720\) resolution) mean a heavily unbalanced workload distribution, which will probably lead to low parallel efficiencies. As we will see later, the election of an unbalanced layout may lead to underwhelming results. An N/A value in the table means that the corresponding layout is not possible for that resolution. For example, a division of a frame using a \(1\times 10\) layout (1 column, 10 rows) is not possible for the \(832\times 480\) resolution, where there are only 8 rows of CTUs in a frame.