How to Contribute to GStreamer

This document provides instructions and guidelines for submitting issues, feature requests and patches to GStreamer. The following applies to all these operations:

  • Please use freedesktop.org GitLab to perform any of the aforementioned operations. You will need to create a freedesktop.org GitLab account if you don't have one yet (yep, that's just how it is. Sorry for the inconvenience) If you don't want to create a new account you should also be able to sign in with a Google, GitHub or Twitter account.

How to File Issues and Request for Enhancements

Where to File Issues and Feature Requests

  • Create a new issue if there is no existing report for this problem yet. The GStreamer bugs page also has shortcuts for the major components and simple search functionality if you'd like to browse or search for existing issues, or use the GitLab search bar for the GStreamer project at the top of the page.

  • If you are filing a feature request (i.e. anything that is not supposed to work already, that is anything not an issue), please add the Enhancement label. Feel free to add any other appropriate already existing labels. Please don't create new labels just for your issue. This won't affect the way we prioritise the issue, but it will make triaging easier for us. In particular, do not add the Blocker label to an issue just because an issue is important to you. This label should be added only by GStreamer maintainers.

  • If your issue is about a specific plugin, element or utility library, please prefix the issue summary with element-name:, plugin-name: or lib: and keep the rest of the description as short and precise as possible.

    Examples:

    • id3demux: fails to extract composer tags
    • tsdemux: does not detect audio stream
    • Internal flow error when playing matroska file

    This makes sure developers looking through the list of open issues or issue notification mails can quickly identify what your issue is about. If your text is too long and only contains fill words at the beginning, the important information will be cut off and not show up in the list view or mail client.

  • If you don't know which component to file the issue against, just pick the one that seems the most likely to you, or file it against the gstreamer-project component. If in doubt just pop into our IRC channel #gstreamer on the freenode IRC network, which you can connect to using any IRC client application or the freenode IRC webchat. In any case, if it's not the right component someone will move the issue once they have a better idea what the problem is and where it belongs.

  • Please mention:

    • what version of GStreamer you are using
    • what operating system you are using (Windows, macOS, Linux)
    • if you're on Linux, please mention your distro and distro version
    • if this is on an embedded device please provide details
  • Try to describe how the issue can be reproduced. If it is triggered by any specific file, try to make the file available somewhere for download and put the link into the issue. The easier it is for us to reproduce the issue, the easier it is to fix it.

  • If you experience a crash (that is: the application shuts down unexpectedly, usually with a segfault or bus error or memory access violation or such), please try to obtain a stack trace. If there are criticals or warnings printed right before the crash, run with the environment variable G_DEBUG=fatal_warnings set, then it will abort on the first warning, which should hopefully give an indication to where the problem is. You can then obtain a stack trace from where it aborts.

  • If the application errors out, please provide a gst debug log. You can get one by setting the GST_DEBUG=*:6 environment variable, combined with GST_DEBUG_FILE=/tmp/dbg.log. The resulting file might end up being very large, so it's advisable to compress it with xz -9 /tmp/dbg.log before sharing. You may also be asked to provide debug logs for specific debug categories rather than everything (*:6).

How to Submit Patches

Where to Submit Patches

Patches need to be submitted through GitLab in form of a "Merge Request" (MR), which is the same as a "Pull Request" (PR) in GitHub, and uses the same workflow.

In order to submit a merge request you first need a personal fork of the project / gstreamer module in question. To fork a module go to the module in question (e.g. https://gitlab.freedesktop.org/gstreamer/gstreamer) and hit the fork button. A new repository will be created in your user namespace (https://gitlab.freedesktop.org/$USERNAME/gstreamer). You will be redirected there automatically once the forking process is finished. For big repositories the forking might take a few minutes.

Once this is done you can add your personal fork as new remote to your existing checkout with

git remote add my-personal-gitlab-fork git@gitlab.freedesktop.org:$USERNAME/gstreamer.git

Check with

git fetch my-personal-gitlab-fork

that it is accessible and working.

If you have not done so already, you may need to first set up SSH keys in your GitLab User Settings.

Next, you make a git branch with one or more commits you want to submit for review and merging. For that you will first need a local branch which you can create with e.g.

git checkout -b fix-xyz

You can then push that branch to your personal fork git repository with

git push my-personal-gitlab-fork

You can use

git push --dry-run my-personal-gitlab-fork

for testing to see what would happen without actually doing anything yet.

After you have pushed the branch to your personal fork you will see a link on the terminal with which you can create a merge request for the upstream repository. You can also do this later by going to the branch list of your personal repository at https://gitlab.freedesktop.org/$USERNAME/gstreamer/branches and then hitting the 'Merge Request' button when ready. This will open a new page where you can enter a description of the changes you are submitting.

Couple of additional points:

  • If you are submitting a Merge Request for an issue (or multiple issues) that already exist, please add 'Fixes #123' to the commit message of one of your commits, so that there is a cross-reference in GitLab and the issue will be closed automatically when your Merge Request is merged.

  • You do not have to file an issue to go with each Merge Request, it's fine to just submit a Merge Request on its own.

  • Please enable the "Allow commits from members who can merge to the target branch" checkbox when submitting merge requests as otherwise maintainers can't rebase your Merge Request when they want to merge it, which means they won't be able to merge it.

  • If your proposed changes are proposed for review but not ready to be merged yet, please prefix the Merge Request title with WIP: for Work-in-Progress. That will prevent us from inadvertently merging it and make clear its status.

  • Please make sure the 'Author' field in your commit messages has your full and proper name and e-mail address. You can check with e.g. git log or gitk.

  • If your change is for an enhancement (anything that is not supposed to work already, i.e. anything not a bug) or adds new API, please add the Enhancement label. This won't affect the way we prioritise your issue, but it does make triaging easier for us.

  • If your Merge Request is against a specific plugin or element or utility library, please prefix the Merge Request summary with element-name:, plugin-name: or lib: and keep the rest of the description as short and precise as possible.

    Examples:

    • id3demux: add support for WCOP frame
    • riff: add RGB16 support
    • playbin: detect if video-sink supports deinterlacing
    • tests: rtprtx unit test is racy

    This makes sure developers looking through the list of open merge requests or notification mails can quickly identify what your change is about. If your text is too long and only contains fill words at the beginning, the important information will be cut off and not show up in the list view or mail client.

  • Make liberal use of the reference syntax available to help cross-linking different issues and merge requests. e.g. #100 references issue 100 in the current module. !100 references merge request 100 in the current project. A complete list is available from gitlab's documentation.

  • Please create separate merge requests for separate issues and for different modules. There is no golden rule when something counts as a separate issue, please just use your best judgment. If a merge request is related to another merge request in another module please mention that in the description using a gitlab reference as outlined above. For example, if you have a change that needs to be done in each module, one issue with one merge request per module is fine. If there is an issue that requires related fixes in multiple elements or libraries, please also feel free to put everything into one issue. If you just happen to have multiple patches for us but they are not really related, please put them in separate issues and merge requests. The main question is if it makes sense to discuss and review these patches together or if they could just as well be handled completely separately.

  • Please do not send patches to the gstreamer-devel mailing list. Patches submitted on the mailing list are most likely going to be ignored, overlooked, or you will get a brief reply asking you to put them into gitlab. We do not use the mailing list for patch review.

  • Please do not send pull requests to our github mirror. They will be closed automatically.

  • Please do not attach patches to existing bugs on GNOME Bugzilla If you want to reopen an already closed bug, let one of the developers know and we will look into that on a case-by-case basis.

  • Please do not attach patches to issues.

How to Prepare a Merge Request for Submission

If possible at all, you should prepare a merge request against a current git checkout, ideally against the tip of the master branch. The gitlab merge request UI will contain information about whether the merge request can be applied to the current code. If a merge request was prepared against an old commit and does not apply any longer to master you may be asked to provide an updated branch to merge.

If you have created a new plugin, please submit a merge request that adds it to the gst-plugins-bad module, including configure.ac, the various Makefile.am modifications, meson.build modifications, and all new files.

Patch Format

The easiest way to create a merge request is to create one or more local commits for your changes in a branch in a local git repository. This should be a git clone checkout of your fork of the module in question. To fork a module go to the module in question (e.g. https://gitlab.freedesktop.org/gstreamer/gstreamer) and hit the fork button. A new repository will be created in your user namespace and should be accessible as https://gitlab.freedesktop.org/$USERNAME/gstreamer. You should clone this repository with valid ssh credentials to be able to automatically push code to your fork.

Once you have a git repository with the original code in it, you should create a branch for your change. e.g. to create a branch and checkout:

git checkout -b topic-branch

Then you can make your modifications and create a local commit with e.g.

git commit path/to/file1.[ch]

This will pop up an editor where you can create your commit message. It should look something like:

exampledemux: fix seeking without index in push mode

Without an index we would refuse to seek in push mode. Make
seeking without an index work by estimating the position
to seek to. It might not be 100% accurate, but better than
nothing.

https://bugzilla.gnome.org/show_bug.cgi?id=987654

Then exit the editor, and you should have a commit.

It's best to run git add or git commit on specific directories or files instead of using git commit -a, as it's too easy to accidentally contaminate a patch with changes that belong into it with git commit -a, in particular changes to the common submodule.

You can check your commit(s) with git show or git log -p or using a GUI such as gitg or gitk.

Make sure the author is correctly set to your full name and e-mail address.

If you haven't used git before, it would be a good idea to tell it who you are:

$ git config --global user.name "George S. Treamer"
$ git config --global user.email "george.s.treamer@example.com"

You can make changes to the last commit using:

  • git commit --amend to fix up the commit message

  • git commit --amend --author='John You <john@you.com>' to fix up the author

  • git add path/to/file1.[ch]; git commit --amend to incorporate fixes made to the files since the last commit (i.e. what shows up in git diff). If you just want to add some of the changes, but not all of them you can use git add -p file.c, then it will ask you for each individual change whether you want to add it or leave it.

Once everything looks fine, push your branch to your local fork e.g. using

git push your-personal-gitlab-fork your-branch

This push will display a link to be able create a merge request from your branch. Click this link and fill out the details of the merge request. You can also create a merge request from an existing branch. See the gitlab documentation for more details.

Please make sure your commits are as terse and precise as possible. Do not include 'clean-ups' or non-functional changes, since they distract from the real changes and make things harder to review, and also lower the chances that the patch will still apply cleanly to the latest version in git. If you feel there are things to clean up, please submit the clean-ups as a separate patch that does not contain any functional changes.

Try to stick to the GStreamer indentation and coding style. There is a script called gst-indent which you can run over your .c or .cpp files if you want your code auto-indented before making the patch. The script requires GNU indent to be installed already. Please do not run gst-indent on header files, our header file indentation is free-form. If you build GStreamer from git, a local commit hook will be installed that checks if your commit conforms to the required style (also using GNU indent).

Writing Good Commit Messages

Please take the time to write good and concise commit messages.

The first line of each commit message should be a short and concise summary of the commit. If the commit applies to a specific subsystem, library, plugin or element, prefix the message with the name of the component, for example:

oggdemux: fix granulepos query for the old theora bitstream

or

docs: add new stream API

or

tests: video: add unit test for converting RGB to XYZ colorspace

This should be a summary of the change and not a description of the change. Meaning: don't say how you did something but what you fixed, improved or changed, what the most important practical effect of the change is. Example:

qtdemux: fix crash when doing reverse playback in push mode (good)

instead of

qtdemux: use signed integer to avoid counter underrun (bad)

The second line of the commit message should be empty.

The third and following lines should contain an extensive description and rationale of the change made: what was changed, what was broken, how did it get fixed, what bugs or issues does this fix? And most importantly: why was something changed.

Trivial commits do not require a description, e.g. if you fix a memory leak it's usually enough to just say that you fixed a leak. Maybe mention what was leaked and perhaps also if it was an important leak or only happens in some corner case error code path, but in any case there's no need to write a long explanation why leaks are bad or why this needed fixing.

The important part is really what the reasoning behind the change is, since that's what people want to know if they try to figure out twelve months later why a line of code does what it does.

If the commit is related to any particular issues in gitlab, please add the full issue URL at the end of the commit message.

https://gitlab.freedesktop.org/gstreamer/gstreamer/issues/123

We do not use Signed-off by: lines in GStreamer, please create commits without those.

After Submitting your Merge Request

Whenever you submit a new Merge Request, add a comment to an existing issue or Merge Request, GitLab will send a notification e-mail to GStreamer developers. This means that there is usually no need to advertise the fact that you have done so in other forums such as on IRC or on the mailing list, unless you have been asked to file an issue there, in which case it's nice to follow up with the link to the issue.

Most of all, please be patient.

We try to review patches as quickly as possible, but there is such a high turnaround of issues, merge requests and feature requests that it is not always possible to tend to them all as quickly as we'd like. This is especially true for completely new plugins or new features.

If you haven't received any response at all for a while (say two weeks or so), do feel free to ping developers by posting a quick follow-up comment on the issue or merge request.

If you do not get a response, this is usually not a sign of people ignoring the issue, but usually just means that it's fallen through the cracks or people have been busy with other things.

Updating Your Merge Request and Addressing Review Comments

When someone reviews your changes, they may leave review comments for particular sections of code or in general. These will usually each start a new "Discussion" which is basically a thread for each comment.

When you believe that you have addressed the issue raised in a discussion, either by updating the code or answering the questions raised, you should "Resolve the Discussion" using the button.

This way it is easy to see for maintainers and for yourself what's left to do and if there are any open questions/issues.

Whenever you have made changes to your patches locally you can just git push -f your-personal-gitlab-fork your-branch to your personal fork, and GitLab will pick up the changes automatically. You do not need to submit a new Merge Request whenever you make changes to an already-submitted patchset, and in fact you shouldn't do that because it means all the previous discussion context is lost and it's also not easy for reviewers to see what changed. Just update your existing branch.

Workflows for GStreamer developers

Backporting to a stable branch

Before backporting any changes to a stable branch, they should first be applied to the master branch, and should obviously not have caused any known outstanding regressions. The only exception here are changes that do not apply to the master branch anymore.

Existing merge request against the master branch, including merged ones, that should be considered for backporting in the future should be labeled with the Needs backport label unless there is any specific urgency to get it backported. All merge requests with the Needs backport label will be regularly considered for backporting by GStreamer developers.

Creating a merge request for backports

When creating a merge request for backporting changes, include one or more changes in the merge request and ideally all from the Needs backport list after reviewing them and potentially fixing them to work cleanly with the stable branch.

If there are specific commits or areas of commits where further feedback is needed, please create a task list in the description of the merge request and @ the committer or whoever has knowledge about this commit.

Add another task to the task list in the merge request's description for the module's maintainer(s) to confirm the merge and @ one or more maintainers.

Only once the CI succeeded for the merge request and all tasks are solved, especially the confirmation from the maintainer(s), the merge request can be merged.

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