README.chromium

Name: ffmpeg
URL: http://ffmpeg.org/
License: LGPL 2.1
License File: CREDITS.chromium
Upstream Git: git://source.ffmpeg.org/ffmpeg.git
Last Upstream Merge: adf72718a41943bb62b3fabd5dbe33f5b9a6e63e, Dec 11 2020

This file documents the layout of the Chromium copy of FFmpeg, some common
tasks, and how to create the build files and related configurations.

FFmpeg Layout:
==============

Chromium's copy of FFmpeg is a fork of the upstream git repository, see the
tags above for the latest merged upstream revision.  All of the
Chromium-specific bits, minus the gn files, are located under the chromium/
folder off the root.

    BUILD.gn: Has the targets for building FFmpeg for Chrome.

    ffmpeg_generated.gni: Pregenerated listing of files necessary to build
      every platform.  See chromium/scripts/generate_gn.py for more details.

    chromium/scripts: Utilities for building the gn and config files.

    chromium/config/...: Pregenerated FFmpeg config options for each platform
      and architecture; e.g., ChromeOS: ARM-Neon, Linux: X64, etc.

    chromium/patches/README: Details of Chromium-specific changes that haven't
      yet made it upstream.


Help w/ Common Tasks:
=====================

-- Submitting changes to Chromium's FFmpeg Git repository.

The goal of Chromium's FFmpeg repository is to just be a mirror of the upstream
Git repository.  This means every change made must be upstreamed.  If you make
a change, please add an entry to chromium/patches/README with a link to the
tracking issue and code review for your change. Reviews are performed with
Gerrit at https://chromium-review.googlesource.com.

  1) Create a branch and make a local, single commit. Gerrit differs from
     Rietveld in that you must have a single commit, so use git commit --amend
     if you need to make changes. Verify that your commit contains a
     Change-Id field, which is how Gerrit coalesces separate patch sets into the
     same code review.

  2) Upload for review:
     git cl upload

  3) Commit via https://chromium-review.googlesource.com once approved.

  4) If needed, submit a Chromium-side change to update DEPS.

-- Upstreaming a patch.

  <checkout copy of upstream repo>
  git checkout <hash of last Chromium FFmpeg, see tag above> -b my_patch
  git apply <patch. pulled from code review or cherry-picked from this repo>
  git rebase origin/master
  < Follow FFmpeg guide: http://ffmpeg.org/developer.html#Submitting-patches-1 >

Once your change has been upstreamed, please update the chromium/patches/README
file with the status.  The next time an upstream merge is done, the committer
will clear out all the patches which have been upstreamed.

-- Cherry-picking a patch from upstream.

  # Tell our repo about the upstream one.
  git remote add upstream git://source.ffmpeg.org/ffmpeg.git
  git fetch upstream

  # Create a new branch based off of master for committing our patch.
  git checkout origin/master -b my_new_branch

  # Pull the patch out of upstream.
  git cherry-pick -x <hash of commit in upstream>

  <Follow rest of "Submitting changes to Chromium's FFmpeg Git repository.">


Performing An Upstream Merge
============================

Currently this is an extremely tedious process that requires access to a Linux,
Mac, and Windows development machine and lot of blood, sweat, and tears.

The instructions are also prone to going stale, so in the interest of
collaboration and sharing tips we have moved to a public document:
https://docs.google.com/a/chromium.org/document/d/14bqZ9NISsyEO3948wehhJ7wc9deTIz-yHUhF1MQp7Po/edit#