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Bug#1103936: Bug# #1103936 ffmpeg: Wrong result for h264 encoding on ppc64el



Hi Trupti,

On Fri, 22 Aug 2025 10:57:12 +0530 Trupti <trupti@linux.ibm.com> wrote:
I've investigated this build failure on ppc64el and have confirmed the root cause is a bug in the Altivec code within libx264.

While recompiling libx264 with assembly disabled (--disable-asm) fixes the build, it's not a viable solution due to a massive performance regression. A benchmark I ran showed that the:
6.9s with Altivec and 54.3s without Altivec .

Given the performance impact, how would you recommend we proceed with resolving this?

I am not involved in libx264 maintenance, I'm lurking as a Release Team member. Reporting upstream sounds like a smart move, maybe upstream already even found and fixed the issue, if not they may be helpful. I guess somebody with knowledge of ppc64el assembly needs to have a look and come up with a patch. Seems like a fitting job for a porter.

An alternative route is to check for newer upstream versions. This library hasn't seen a Debian update since one year ago. Might be that the problem is already fixed.

Paul

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