Detailed white-paper on our results from AVX512 acceleration

By Pradeep Ramachandran

A month or so back, we published a white-paper that gave high-level results on the encoder gains that we saw from our recently implemented AVX512 kernels in x265. We have now published a more detailed paper that tears the results down into more detail, including per-kernel gains for AVX512 over AVX2. The paper can be accessed from here. We hope you find the detailed analysis more informative to understand the reasons behind the results that you see on your hardware.

Do share your findings with us. As you have probably already noticed, AVX512 is part of the recently-released v2.8 of x265!

x265 Version 2.8 Released

x265 version 2.8 with cool new features including AVX512 accelerating, dynamic refinement (that enables optimized encoding for ABR streaming), support for measuring VMAF has been released! More details in our release notes at

x265 turns 5!

As it turns out, the x265 project turned 5 a couple of months back; our first commits from the HM encoder date back to March, 2013. And being the geeks that we are, we didn’t even realize it!

Many thanks to all those who have enabled x265 accomplish all that it has over 5 years! We continue to innovate inside x265 to improve both quailty, and performance and look forward to celebrating our 10th anniversary with you.



Thanks for a great NAB 2018

By Pradeep Ramachandran

Now that the dust has settled, it is time to thank all the contributors for enabling a great showing by x265 at NAB 2018. We showed-off our new ML-accelerated content adaptive encoding for ABR, AVX-512 acceleration, and the recently added support for HDR10+/HLG at NAB. We received great feedback on what people would like to see in the coming releases, and will be working hard to continue to innovate in that space. We’ve also formed a committee to guide the future development of x265, and other open source media codecs that we will blog about more in the coming weeks; read this article for an initial idea of what this is about.

Until our next showing, don’t hesitate to reach out to us on the developer mailing list, doom9 (), or Facebook to talk.

And finally, avx512 in x265!

By Pradeep Ramachandran

Finally, the acceleration that we’ve all been waiting for is here! We’ve been working extensively with Intel for the last few months to use Intel Advanced Vector Extensions 512 (AVX-512) to accelerate x265. After much effort, we’re delighted to share that we’ve been able to accelerate 4K HDR encoding in main10 profile by over 15% for high-quality offline encoding. Checkout this white-paper on the Intel site for more information.

The patches will be pushed to the default branch soon. Let us know the results of your tests – you know where to find us!

Excited about AV1 closing doors, but…

By Pradeep Ramachandran

After what seems to have been a long delay, AV1 finally froze its bitstream last week! Like many folks in the industry, we have been waiting for this moment for a long time to see what a truly ‘royalty-free’ codec can can bring in terms of tools to the encoding space.

A few months ago, we stopped looking further into how AV1’s tools compare to that of HEVC due to this peer-review paper  published in a leading journal from leading researchers in the field of video coding. That paper reported that the HM encoder provide average bitrate savings of 30% relative to AV1 with an encoding speed that was 25X that of the AV1 encoder; the informed would know that x265’s veryslow is very comparable in encoder efficiency to the HM encoder. While optimizations could bridge the gap in speed, bridging the gap in encoder efficiency would be hard unless some fundamental improvements (that are not covered by the HEVC-patents, mind you) are made. Now that the bitstream is frozen, we will be digging to see what new tools have been brought to the table that were not included in this comparison in the hope to answer the question “Is AV1 fundamentally better than HEVC as a standard?”. Stay tuned here to hear more, or share your thoughts on doom9/x265-devel mailing list.

And of course, there is the issue of patent royalties and licensing, but we will leave that up to the lawyers to deliberate and decide; lets talk more tech here!

NAB 2018, of course we will be there!

By Pradeep Ramachandran

MulticoreWare, the developers of x265, will be available to discuss all things media at NAB 2018 in Las Vegas from April 9th – 12th in their booth at SU-14708. Swing by to talk about the soon-to-publish AVX512 acceleration, content adaptive optimizations for ABR encoding with x265, or if you just want a selfie with the creators of the world’s most popular HEVC encoder.

See you in Vegas!

PS: Make sure to mention this blog post if you stop by to stand a chance to win some open-source memorabilia!

x265 version 2.7 released!

By Ashok Kumar Mishra

x265 version 2.7 is now out! The key new improvements include support for RADL pictures, moving from YASM to NASM assembler and reduced x265 build time by more than 50%.

The tarball of this release can be downloaded from here. The latest release notes are available here.

Happy Compressing!

x265 Incorrectly Represented in MSU’s 2017 Codec Comparison I

By Pradeep Ramachandran

MSU recently released their 2017 codec comparison, where they compared x265 against other HEVC encoders, VP9 encoders, and the AV1 encoder. While the efforts that go into such large scale tests are appreciated, we as the x265 developers have to respectfully disagree with your conclusions drawn from this MSU report as we believe it is incomplete.

If you notice, these tests use v1.9 of x265 which is over 20months old! Since then, x265 has had 7 versions with an imminent 8th version. As anyone would expect, x265 has made considerable progress in speed and quality during this time. Specifically, we’ve made big changes to the lambda tables which considerably improved visual quality as reported by both consumers and customers.

That said, it is possible that maybe AV1 is a better codec than HEVC (at least in quality); maybe so is VP9. Maybe they have tools that are competent and can challenge HEVC. However, for the above said reasons, these results do not conclusively prove so, in our opinion!

Now as to why MSU used a 20month old encoder, there is some history there about the reservations of the x265 team to the validity of MSUs past tests as only objective scores were looked at. Quoting my dear friend, ‘we look at video and not at graphs!’. It is encouraging to see the MSU tests taking a turn towards doing subjective testing, which, in our opinion, is the right direction. Hopefully we will work with their newly mended ways in future for a more fair and realistic evaluation!

x265 version 2.6 released

By Pradeep Ramachandran

New features
1) x265 can now refine analysis from a previous HEVC encode (using options –refine-inter, and –refine-intra), or a previous AVC encode (using option –refine-mv-type). The previous encode’s information can be packaged using the x265_analysis_data_t data field available in the x265_picture object.
2) Basic support for segmented (or chunked) encoding added with –vbv-end that can specify the status of CPB at the end of a segment. String this together with –vbv-init to encode a title as chunks while maintaining VBV compliance!
3) –force-flush can be used to trigger a premature flush of the encoder. This option is beneficial when input is known to be bursty, and may be at a rate slower than the encoder.
4) Experimental feature –lowpass-dct that uses truncated DCT for transformation.
Encoder enhancements
1) Slice-parallel mode gets a significant boost in performance, particularly in low-latency mode.
2) x265 now officially supported on VS2017.
3) x265 now supports all depths from mono0 to mono16 for Y4M format.
API changes
1) Options that modified PPS dynamically (–opt-qp-pps and –opt-ref-list-length-pps) are now disabled by default to enable users to save bits by not sending headers. If these options are enabled, headers have to be repeated for every GOP.
2) Rate-control and analysis parameters can dynamically be reconfigured simultaneously via the x265_encoder_reconfig API.
3) New API functions to extract intermediate information such as slice-type, scenecut information, reference frames, etc. are now available. This information may be beneficial to integrating applications that are attempting to perform content-adaptive encoding. Refer to documentation on x265_get_slicetype_poc_and_scenecut, and x265_get_ref_frame_list for more details and suggested usage.
4) A new API to pass supplemental CTU information to x265 to influence analysis decisions has been added. Refer to documentation on x265_encoder_ctu_info for more details.
Bug fixes
1) Bug fixes when –slices is used with VBV settings.
2) Minor memory leak fixed for HDR10+ builds, and default x265 when pools option is specified.
3) HDR10+ bug fix to remove dependence on poc counter to select meta-data information.