November 15, 2017
By Jan Ozer 特约编辑
专题文章

HLS中的HEVC:它如何影响设备性能?

If you're considering adding HEVC to your HTTP Live Streaming (HLS) videos, 其中一个问题是播放视频所需的CPU, 因为这会影响播放帧率和电池寿命. To prepare for a 流媒体西部 pre-conference session on producing HLS with HEVC (co-produced with David Hassoun and Jun Heider from Realeyes Media)，我们比较了H.264 and HEVC playback on two phones and three computers, using files prepared and hosted for us by Bitmovin. It's not a lot of data, but we found it both interesting and useful.

To start, 让我们来看看iOS 11的兼容性矩阵, which is what you'll need to playback HEVC and HLS on iOS devices like iPhones and iPads.

Figure 1. iOS 11兼容性矩阵来自 Apple

iPhone 6

As Figure 1 shows, iOS 11可以在iPhone SE/5S这样的老手机上运行, 但我们测试的最老的手机是iPhone 6, 第一个用HEVC硬件解码. Specifically, we used the System Status App to capture the processor utilization charts shown in Figure 2 大约两分钟的视频播放. On the left is H.264，右边的HEVC.

As you can see, H.H . 264期间的平均利用率约为50%.264播放，而HEVC则略微超过60%. As you may remember, 苹果在iPhone 6上为FaceTime添加了HEVC播放功能, and it seems like it’s being used for HEVC playback with HLS as well. Still, 基于这个实验, you would expect some minor decrease in playback time with HEVC as opposed to H.264, though that’s difficult to estimate based solely upon CPU utilization.

Figure 2. iPhone 6的CPU利用率

iPhone 7

如果你已经升级到iPhone 7, however, 您会发现CPU需求非常相似, as you can see in Figure 3. 如果你已经升级到iPhone 8或iPhone X, 使用比iPhone 7更先进的处理器, 你不会期望太多, if any, 电池寿命受HEVC影响.

Figure 3. CPU consumed by H.264和HEVC在iPhone 7上

What About iPads?

这与当前的iPad型号有何关系? 因为我们没有单元可以测试，所以我们只能推测. Note that the iPhone 6 uses Apple A8 system on a chip (SoC), 和iPad mini 4一样, so you'd expect a similar increase in CPU utilization on the mini 4. 标准版iPad使用的是A9芯片, 哪个应该比A8更有效率, 但我们没有相关数据. The 10.5" and 12.9英寸的iPad Pro使用A10X, 哪个比iPhone 7的CPU更先进, so both these devices should be at least as efficient as the iPhone 7, 这意味着HEVC对电池的影响很小或没有影响.

Regarding iPhones, iPhone 5使用的是苹果A6 SoC, 比iPhone 6使用的A8晚了两代, 并且没有HEVC加速. 我希望CPU利用率远高于H.264, but you never know until you test (and if you have tested, please let us know in a comment). When you consider that the iPhone 5 shipped more than five years ago in September 2012, this model is likely not a concern for most streaming producers.

Overall, 不过我们对iPhone的测试有限, it appears that deploying HEVC within HLS will have minimal impact on most devices, iPhone 7和更新的手机绝对没有, 以及可能使用相同soc的ipad.

电脑怎么样??

2010年iMac和High Sierra

Figure 4 显示High Sierra的兼容性矩阵, 为了在HLS中支持HEVC，您需要升级到哪个版本.

Figure 4. 你需要一台这样的电脑才能在HLS中播放HEVC.

On a 2010 iMac that barely snuck into the compatibility grid, CPU利用率在HEVC和H之间非常一致.264，如你所见 Figure 5. This could be because this computer was equipped with an ATI Radeon HD 5670 graphics engine, though this card pre-dated HEVC so obviously doesn't support HEVC decoding. Of course, battery life doesn't matter on a device that only works when plugged in, but it was good to see that the video played at or close to full frame rate.

Figure 5. 两种格式在2010年iMac上的CPU负载.

MacBook Pro和High Sierra

MacBook Pro没有漂亮的图片, where we had to rely up CPU-related results from Activity Monitor to distinguish the playback load between the two formats. Our mid-2014 notebook had a four-core Core i5 CPU with Intel Iris graphics. On this notebook, overall CPU utilization was around 44% for H.264和50%的HEVC, 这应该会导致电池寿命的减少, 但可能不是戏剧性的.

MacBook Air

看看图4所示的计算机, 最年长的一代令人担忧, since they're equipped with intel Core 2 Duo CPUs that lack the hyperthreading and other architectural advancements of the newer Intel Core i3 and i5 CPUs. However, in 2011, the MacBook and MacBook Air notebooks got a refresh to a Core i5 CPU with more than sufficient power for either H.264 or HEVC.

For example, the last computer we tested was a 2011 MacBook Air with a 1.6 GHz Intel Core i5, and you can see the CPU required for playback of the two formats in Figure 6. Again, 差异大约是整个CPU的7%, but it’s clear that even this six-year-old computer had plenty of power to spare.

Figure 6. 2011年MacBook Air 1的播放CPU.6 GHz Intel酷睿i5 CPU

Overall, while you may have issues with the oldest generation of supported mobile devices and computers, the next generation in all cases show only a slight increase in CPU utilization for HEVC playback, 而新款iphone至少表现出了相对的平价. Publishers considering deploying HEVC should do so without concerns that the higher-end format will create significant battery life issues for most potential viewers.