Contributing to x264

Another project I contribute to is x264. As per the previous post on the topic I’ll try to summarize how things work.


Coding style

x264 has a coding style and on review you will get asked to follow it, sadly the sources do not contain a document about it, you have to look around the code and match what is there.


x264 has an amazing test harness that doubles as benchmark harness to add support for additional architecture-specific optimizations. checkasm is really good in helping you write new code for this kind of purpose and make sure it is really faster.

It is automatic to use if you are adding a function already implemented in other architectures, if you want to extend the coverage for something new it is moderately difficult, mainly because you have to read the code since no documentation is available otherwise.

Submitting patches

Submitting code to x264 requires you to sign a cla, the process is sort of manual and involves exchanging emails with the person in charge to provide and collect the cla pdf once you signed it.

Once you are done on that you should rebase your changes over the sandbox branch, that’s somehow similar to the next branch on other projects and send them to the developer mailing list using git send-email.


The review process will happen in the mailing list and you are supposed to be subscribed to it and interact with the reviewers there.


  • Mimic the coding style used in the project and hope you get it right
  • Peruse checkasm to make sure what you are doing works as intended and it is fast
  • Subscribe to the developer mailing list and learn how to use git send-email.
  • Be patient and wait for review comments in the mail box.