HEVC vs. H.264: Bandwidth and Cost Savings

The case for moving from ubiquitous older video codecs like H.264 (AVC) to newer codecs like AV1 or HEVC (H.265) 通常用编码效率来表示，从而转化为带宽和成本节约. For major content companies like Warner Bros. Discovery that have adopted H.265，他们的经历在多大程度上证实了这个假设? In this clip from Streaming Media Connect 2023, Streaming Learning Center’s Jan Ozer and Alex Zambelli, Technical Product Manager at Warner Bros. Discovery, discuss the real-world ramifications of H.264-to-H.265迁移，其中已实现的回报已被证明是显著的，并且它不太明显. As it turns out, 采用一个闪亮的新编解码器来进行明显低于4k的编码和传输，当在编码阶梯上的所有阶梯上平均时，并不总是值得的.

在回答Ozer关于WBD在哪些方面看到了节省的开放式问题时 HEVC over H.264, Zambelli explains that it varies “depending on resolution. When you're looking at HD resolutions and 4K resolutions, 有时候，HEVC比AVC更容易节省25%到40%的成本. 因此，我们期望从HEVC中获得的各种节省的承诺在更高的分辨率下确实实现了. 但是当你降低分辨率时你仍然需要支持一个完整的编码阶梯, and so often you find yourself encoding 320x180 video, the bitrate savings are not as huge. And so I would say across the board, 比特率的平均节省可能比AVC接近15%或20%.

以获得实际的成本节省——这只是部分地与带宽节省成比例地增加, 由于其他因素也在起作用，ozer要求Zambelli考虑并评论两个成本——“编码两种格式和缓存效率”——以及它们是如何影响的. 

事实证明，与HEVC编码相关的计算成本的增加在一定程度上减少了迁移到较新的编解码器的好处, 尽管向云计算的转变和编码器的改进有助于公平竞争. "There are certainly higher compute costs for HEVC," Zambelli says, “尽管我认为编码器在过去几年里已经变得更好了. 而且，大多数云计算平台在CPU产品方面都有所改进, 所以我们在云端拥有高度多线程的cpu. 现在大多数编码也是并行的，”他解释道. “所以，如果你正在构建一个视频转码平台，需要处理大量内容, you're going to parallelize it so that you're not necessarily encoding one video in one machine; you're going to spread it out across multiple machines. 所以当我们这样做的时候，计算成本从HEVC增加了. It's certainly there, 但它并没有重要到阻止我们做HEVC," he explains. “所以我们肯定会到达一个点，我认为HEVC编码将变得足够便宜，它几乎就像一个免费的附加组件, on top of the AVC encoding."

As for the fragmentation of caching, Zambelli says, “I haven't seen much of an impact from that, because all of our devices support AVC, and so obviously that's going to be highly cached. Over 75% of the devices support HEVC, 所以HEVC的缓存效率也很高. 所以我想说，我们没有看到缓存碎片对体验质量的任何负面影响.”

谈到底线，Ozer问道:“成本呢? Aren’t you paying for two times the caching?”

Zambelli’s response: it’s complicated. “我觉得很多时候，人们都认为CDN成本节约和更高级编解码器的速率节约之间存在直接的一对一映射. 但我发现事实并非如此。. “Because if everybody in the world had unlimited bandwidth, if we all had unlimited connection speeds, then that would perhaps be true. But in reality, if you reduce the barrier, for example, 你的1080p编码从每秒6兆AVC下降到, let's say, 4.5 Mbps in HEVC, 使用3mb连接的用户仍然可以获得3mb的视频. 所以你不一定会减少你提供给这些人的数据量. And as it turns out, 还有很多人——不仅在美国，而且在世界各地——的连接速度低于每秒4或5兆比特. 所以真正的CDN节省最终可能接近5%或10%如果你节省20%的比特率. 所以这两者之间肯定不是一对一的映射.”

Learn more about the the state of video codecs at the next Streaming Media Connect in November 2023.