ARM Community: x264 on ARM: Bringing a wider application of video conferencing (Part 3) - ARM Community

In part one and part two of this blog series, we introduced the video conferencing use case requirements and performed tuning of x264 for optimal tradeoff between bit rate, frame rate and video quality… In this part, we will test and analyze encode performance for optimal execution on the target ARM platform.

1 Test result of on the target ARM platform
Using the results from the previous step, we test the options “default”, “--preset ultrafast”, “--preset superfast” and “--preset very fast” with our optimal settings on the ARM platform and evaluate the performance against our use case requirements for video conferencing.

1). List of Combinations (settings tested)


2). Result


3). Conclusion
According to above information, we can conclude:


2 Summary of the optimal settings
According to the test results above, we might conclude: when rc-lookahead is set to 1, the bit rate is the minimum and the frame rate is the maximum. When ref is set to 1, the frame rate is increased. When subme is set to 1/0, both frame rate and bit rate are increased. When me is set to dia, the frame rate is increased. When partitions is set to none, the frame is split up into 16x16 macro blocks during compression. This helps to decrease operations. No-8x8dct disables adaptive spatial transform size, which helps to decrease operations too. No-mixed-refs means encoder selects refs on a per-macro block, rather than per-8x8 partition basis. This decreases operations.

So we might thus have the most optimal settings to the real-time encoder for video conferencing application.


3 Configuring x264 with optimal settings
Struct “x264_param_t “is defined in file x264.h and contains all the parameters that the encoding process needs. The parameters have default value. If you want to implement the optimal settings as above, set the following parameters as listed below.


Conclusion
Technologies like ARM NEON SIMD instructions are enabling video to become an ever increasing part of the user experience for consumer electronics by supporting a wide range of encode and decode use cases across an array of products powered by ARM Cortex-A processors. x264 is just one example of the capabilities of ARM NEON technology in action.

Blog Series: x264 on ARM: Bringing a wider application of video conferencing
Part 1
Part 2

Yang Zhang, Home Software engineer - Home Software Enabling team, ARM, Yang has several years of experience working on projects related to video codec, including H.264/AVC, H.263, MPEG4, MPEG2, VC-1 and AVS. She has a deep understanding of video codec algorithm. Being Home Software Engineer , she specializes in the digital multimedia system for ARM Home. Yang graduated from Zhejiang University with the degree of Master. She is currently based in Shanghai, China.

张洋(Yang Zhang) 是ARM的家庭软件工程师. 她拥有多年工作经验并致力于视频编解码领域， 曾经参与了H.264/AVC, H.263, MPEG4, MPEG2, VC-1和AVS等相关项目的开发， 深入理解视频编解码算法。作为家庭软件工程师，她专注于和家庭相关的ARM数字多媒体系统架构技术。 Yang 硕士毕业于浙江大学。 她的工作地点在中国上海.