Telestream帮助启动开源x265/HEVC项目

本周, Telestream 宣布开放源代码的可用性 H.265 (HEVC) 编码器，共同创立和管理的 MulticoreWare公司. I had a chance to speak with Telestream CTO Shawn Carnahan about the venture.

He explained that Telestream first started working with MulticoreWare when it included the x264 编解码器 in several of the company’s encoding tools. While x264 is generally regarded as the highest quality H.264 编解码器, 它缺乏高效的GPU并行化, 所以在多核计算机上不能有效运行. 随着OpenCL在麦金塔上的发展势头, and CUDA acceleration very prevalent on Windows computers, the ability to efficiently utilize these available resources was a priority.

Telestream reached out to MultiCoreWare for assistance with multicore CPU and GPU acceleration. Telestream还涉及到Jason Garrett-Glaser, x264项目的首席开发人员, who provided guidance on how to best apply parallelization to the x264 编解码器. The three-way collaboration worked so well that Telestream decided to apply it to the next generation x265 编解码器.

使用x264编解码器，x264许可由 CoreCodec公司, 通过网站 x264licensing.com该公司同时提供GPL和商业许可证. 短暂的, 在GPL许可下, all products that include the source code must also be open source, which obviously isn’t desirable for commercial products. This is why companies that sell encoders using the x264 编解码器 opt for the commercial license, 哪个没有开源需求.

The new open source HEVC encoder will be offered under similar terms, 可通过x265网站获得许可 x265.org. 当我查看网站的时候, source code was available with an executable that you can download and run from the command line. 和x264一样, Carnahan expects that a robust group of open source and commercial products will soon utilize the new 编解码器.

在结构方面，x265.org website lists Telestream as a “sponsor” and MultiCoreWare in a project coordination role. It appears that Garrett-Glaser and his team will continue to be involved, as one of the project goals is to “build on the x264 编解码器 ... 创造出最好的HEVC (H.世界上最先进的视频编码器.” At the time of this writing, the only two “members” are Telestream and MulticoreWare.

In discussing Telestream’s motivation for sponsoring the project, Carnahan noted that Telestream had frequently licensed third-party 编解码器s for their products, and often “the third-party vendor’s development focus wasn’t the same as ours.“基本上, Telestream的投资, and the investment of other parties he expects to soon join the group, will allow them to help direct the future development of the x265 编解码器.

正如卡纳汉解释的那样, HEVC比AVC复杂得多, and it’s very difficult for any one company to develop HEVC and meet all relevant goals, whether it’s faster-than-real-time performance via parallelization or the ability to ‘fan out,’ or efficiently produce multiple file iterations from a single source for adaptive distribution. This team produced such good results with the quality and performance of x264 that we decided to apply the same principles, 但是涉及到更多的人和更多的用例.”

版税仍然适用

与x264许可一样, any royalties for the commercial license will be exclusive of that sought by the HEVC patent group, and Carnahan had no 信息 as to when such a license may be available, 或者它的项是什么. 他是, 然而, more definitive regarding the performance and quality of the existing HEVC implementation.

尽管编解码器仍然是一个正在进行的工作, Carnahan related that the HEVC 编解码器 was running about 2 times slower than the x264 编解码器 when producing a 1080p file to a comparable signal-to-noise ratio. 具体地说, 使用现有代码, an 8-core computer can encode a 1080p file at between 10-30 frames per second without GPU acceleration. This is good news, since some initial reports pegged HEVC encoding at 10X H.264编码时间. Carnahan also indicated that the speed improvements at this point in development are consistent with the short-term goal of real-time encoding of 1080p content on an 8-core machine with 4X real-time encoding with GPU acceleration.

On the quality front, when encoding most aggressively (e.G速度更慢/质量更高), Carnahan stated that a 1080p HEVC file could deliver equivalent quality to x264 at 50% of the data rate, though that number dropped to a 20-30% bitrate saving when encoding in real time. 这也是个好消息, since several initial reports indicated that 30-35% would be the maximum savings produced by any first-generation HEVC encoder.