Table of Contents
- 1 Introduction
- 2 Basics Usage
- 2.1 Get Git
- 2.2 Cloning the source tree
- 2.3 Updating the source tree to the latest revision
- 2.4 Rebasing your local branches
- 2.5 Adding/removing files/directories
- 2.6 Showing modifications
- 2.7 Inspecting the changelog
- 2.8 Checking source tree status
- 2.9 Committing
- 2.10 Writing a commit message
- 2.11 Preparing a patchset
- 2.12 Sending patches for review
- 2.13 Renaming/moving/copying files or contents of files
- 3 Git configuration
- 4 FFmpeg specific
- 5 gpg key generation
- 6 Pre-push checklist
- 7 Server Issues
This document aims in giving some quick references on a set of useful Git commands. You should always use the extensive and detailed documentation provided directly by Git:
git --help man git
shows you the available subcommands,
git <command> --help man git-<command>
shows information about the subcommand <command>.
Additional information could be found on the Git Reference website.
For more information about the Git project, visit the Git website.
Consult these resources whenever you have problems, they are quite exhaustive.
What follows now is a basic introduction to Git and some FFmpeg-specific guidelines to ease the contribution to the project.
2 Basics Usage
2.1 Get Git
You can get Git from http://git-scm.com/ Most distribution and operating system provide a package for it.
2.2 Cloning the source tree
git clone https://git.ffmpeg.org/ffmpeg.git <target>
This will put the FFmpeg sources into the directory <target>.
git clone email@example.com:ffmpeg <target>
This will put the FFmpeg sources into the directory <target> and let you push back your changes to the remote repository.
git clone firstname.lastname@example.org:ffmpeg-web <target>
This will put the source of the FFmpeg website into the directory <target> and let you push back your changes to the remote repository. (Note that gil stands for GItoLite and is not a typo of git.)
If you don’t have write-access to the ffmpeg-web repository, you can create patches after making a read-only ffmpeg-web clone:
git clone git://ffmpeg.org/ffmpeg-web <target>
Make sure that you do not have Windows line endings in your checkouts, otherwise you may experience spurious compilation failures. One way to achieve this is to run
git config --global core.autocrlf false
2.3 Updating the source tree to the latest revision
git pull (--rebase)
pulls in the latest changes from the tracked branch. The tracked branch can be remote. By default the master branch tracks the branch master in the remote origin.
--rebase (see below) is recommended.
2.4 Rebasing your local branches
git pull --rebase
fetches the changes from the main repository and replays your local commits over it. This is required to keep all your local changes at the top of FFmpeg’s master tree. The master tree will reject pushes with merge commits.
2.5 Adding/removing files/directories
git add [-A] <filename/dirname> git rm [-r] <filename/dirname>
Git needs to get notified of all changes you make to your working directory that makes files appear or disappear. Line moves across files are automatically tracked.
2.6 Showing modifications
git diff <filename(s)>
will show all local modifications in your working directory as unified diff.
2.7 Inspecting the changelog
git log <filename(s)>
You may also use the graphical tools like
or the web interface available at http://source.ffmpeg.org/.
2.8 Checking source tree status
detects all the changes you made and lists what actions will be taken in case of a commit (additions, modifications, deletions, etc.).
git diff --check
to double check your changes before committing them to avoid trouble later on. All experienced developers do this on each and every commit, no matter how small.
Every one of them has been saved from looking like a fool by this many times. It’s very easy for stray debug output or cosmetic modifications to slip in, please avoid problems through this extra level of scrutiny.
For cosmetics-only commits you should get (almost) empty output from
git diff -w -b <filename(s)>
Also check the output of
to make sure you don’t have untracked files or deletions.
git add [-i|-p|-A] <filenames/dirnames>
Make sure you have told Git your name, email address and GPG key
git config --global user.name "My Name" git config --global user.email email@example.com git config --global user.signingkey ABCDEF0123245
Enable signing all commits or use -S
git config --global commit.gpgsign true
Use --global to set the global configuration for all your Git checkouts.
Git will select the changes to the files for commit. Optionally you can use the interactive or the patch mode to select hunk by hunk what should be added to the commit.
Git will commit the selected changes to your current local branch.
You will be prompted for a log message in an editor, which is either set in your personal configuration file through
git config --global core.editor
or set by one of the following environment variables: GIT_EDITOR, VISUAL or EDITOR.
2.10 Writing a commit message
Log messages should be concise but descriptive.
The first line must contain the context, a colon and a very short summary of what the commit does. Details can be added, if necessary, separated by an empty line. These details should not exceed 60-72 characters per line, except when containing code.
Example of a good commit message:
avcodec/cbs: add a helper to read extradata within packet side data Using ff_cbs_read() on the raw buffer will not parse it as extradata, resulting in parsing errors for example when handling ISOBMFF avcC. This helper works around that.
ptr might be NULL
If the summary on the first line is not enough, in the body of the message, explain why you made a change, what you did will be obvious from the changes themselves most of the time. Saying just "bug fix" or "10l" is bad. Remember that people of varying skill levels look at and educate themselves while reading through your code. Don’t include filenames in log messages except in the context, Git provides that information.
If the commit fixes a registered issue, state it in a separate line of the
Fix Trac ticket #42.
The first line will be used to name
the patch by
Common mistakes for the first line, as seen in
git log --oneline
include: missing context at the beginning; description of what the code did
before the patch; line too long or wrapped to the second line.
2.11 Preparing a patchset
git format-patch <commit> [-o directory]
will generate a set of patches for each commit between <commit> and current HEAD. E.g.
git format-patch origin/master
will generate patches for all commits on current branch which are not present in upstream. A useful shortcut is also
git format-patch -n
which will generate patches from last n commits. By default the patches are created in the current directory.
2.12 Sending patches for review
git send-email <commit list|directory>
will send the patches created by
git format-patch or directly
generates them. All the email fields can be configured in the global/local
configuration or overridden by command line.
Note that this tool must often be installed separately (e.g. git-email
package on Debian-based distros).
2.13 Renaming/moving/copying files or contents of files
Git automatically tracks such changes, making those normal commits.
mv/cp path/file otherpath/otherfile git add [-A] . git commit
3 Git configuration
In order to simplify a few workflows, it is advisable to configure both your personal Git installation and your local FFmpeg repository.
3.1 Personal Git installation
Add the following to your ~/.gitconfig to help
git format-patch detect renames:
[diff] renames = copy
3.2 Repository configuration
In order to have
git send-email automatically send patches
to the ffmpeg-devel mailing list, add the following stanza
[sendemail] to = firstname.lastname@example.org
4 FFmpeg specific
4.1 Reverting broken commits
git reset <commit>
git reset will uncommit the changes till <commit> rewriting
the current branch history.
git commit --amend
allows one to amend the last commit details quickly.
git rebase -i origin/master
will replay local commits over the main repository allowing to edit, merge or remove some of them in the process.
git commit --amend and
rewrite history, so you should use them ONLY on your local or topic branches.
The main repository will reject those changes.
git revert <commit>
git revert will generate a revert commit. This will not make the
faulty commit disappear from the history.
4.2 Pushing changes to remote trees
git push origin master --dry-run
Will simulate a push of the local master branch to the default remote (origin). And list which branches and ranges or commits would have been pushed. Git will prevent you from pushing changes if the local and remote trees are out of sync. Refer to Updating the source tree to the latest revision.
git remote add <name> <url>
Will add additional remote with a name reference, it is useful if you want to push your local branch for review on a remote host.
git push <remote> <refspec>
Will push the changes to the <remote> repository.
Omitting <refspec> makes
git push update all the remote
branches matching the local ones.
4.3 Finding a specific svn revision
Since version 1.7.1 Git supports ‘:/foo’ syntax for specifying commits based on a regular expression. see man gitrevisions
git show :/'as revision 23456'
will show the svn changeset ‘r23456’. With older Git versions searching in
git log output is the easiest option (especially if a pager with
search capabilities is used).
This commit can be checked out with
git checkout -b svn_23456 :/'as revision 23456'
or for Git < 1.7.1 with
git checkout -b svn_23456 $SHA1
where $SHA1 is the commit hash from the
git log output.
5 gpg key generation
If you have no gpg key yet, we recommend that you create a ed25519 based key as it is small, fast and secure. Especially it results in small signatures in git.
gpg --default-new-key-algo "ed25519/cert,sign+cv25519/encr" --quick-generate-key "email@example.com"
When generating a key, make sure the email specified matches the email used in git as some sites like github consider mismatches a reason to declare such commits unverified. After generating a key you can add it to the MAINTAINER file and upload it to a keyserver.
6 Pre-push checklist
Once you have a set of commits that you feel are ready for pushing, work through the following checklist to doublecheck everything is in proper order. This list tries to be exhaustive. In case you are just pushing a typo in a comment, some of the steps may be unnecessary. Apply your common sense, but if in doubt, err on the side of caution.
First, make sure that the commits and branches you are going to push
match what you want pushed and that nothing is missing, extraneous or
wrong. You can see what will be pushed by running the git push command
with --dry-run first. And then inspecting the commits listed with
git log -p 1234567..987654. The
git status command
may help in finding local changes that have been forgotten to be added.
Next let the code pass through a full run of our test suite.
- if fate fails due to missing samples run
make fate-rsyncand retry
Make sure all your changes have been checked before pushing them, the test suite only checks against regressions and that only to some extend. It does obviously not check newly added features/code to be working unless you have added a test for that (which is recommended).
Also note that every single commit should pass the test suite, not just the result of a series of patches.
Once everything passed, push the changes to your public ffmpeg clone and post a merge request to ffmpeg-devel. You can also push them directly but this is not recommended.
7 Server Issues
Contact the project admins at firstname.lastname@example.org if you have technical problems with the Git server.
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