Posts Tagged ‘git’

From Mercurial to Git and from GoogleCode to GitHub

2012/10/10 2 comments

Some time ago we decided to modify the VCS of our code repository at Google Code from SVN to Mercurial, the only DVCS alternative offered in Google Code (at the time). This system has far more power than non distributed systems and allowed us more freedom to develop on different branches and to merge all the work. But, this decision was made mainly to keep the current repository location rather than by choice, since we prefer to work with Git.

Lately, though, we have been having some problems with Mercurial and that, added to the difficulty to export and import this kind of repository in other code hosting sites, led us to change yet again, this time to Git and to GitHub.

Here are the steps we took in order to do so.

First, make some folders to store the tools and the repositories

cd ~
mkdir repository_conversion
cd repository_conversion
mkdir gitprojectname

Next, make a clone of the mercurial repository in your local machine.

hg clone

This will make a folder projectname with the contents of the repository. Then, download Fast-Export, a tool that converts mercurial repositories into git repositories.

git clone

Before going any further, you should know that Git is more restrictive with the username format of the person doing a commit. Mercurial lets you commit using partial or different username information for the same set of credentials. For example, if you have a committer called John Doe you might find Mercurial commits with the following aliases:

John Doe <>

The correct commit format is the last one (User Name <>), so you should map the wrong aliases to a correct format before converting the repository. To do this, you first need to get the list of all the people that has made a commit in your repository. For that purpose, we can either use the hg log command or the churn extension.

hg log --template "{author}\n" | sort | uniq -c | sort -nr

If you want to use the churn extension instead, you must enable it first in the Mercurial configuration file. You can enable it system-wide editing the /etc/mercurial/hgrc file (or just for your repository editing ~/repository_conversion/projectname/.hg/hgrc) and adding the following to it:

hgext.churn =

Then you can call it like this:

hg churn --template "{author}"

These commands output a list of committers sorted by number of commits. You can copy that list to a text file called to do the user mapping. Following our previous example, you would map John Doe’s aliases like this:

johndoe@dcb55125-116f-0410-8251-c326c5fbc55d=John Doe <> Doe <>
johndoe=John Doe <>
John Doe <>=John Doe <>

Once you are done mapping the users, go to the git repository folder, init a git repository and call the conversion script:

cd ~/repository_conversion/gitprojectname
git init
../fast-export/ -r ../projectname/ -A ../

Depending on the number of commits and branches this process may take a while. Once the conversion is finished, you can check if all the committers were correctly mapped typing:

cd ~/repository_conversion/gitprojectname
git shortlog -nse --all

So, with that we have a fully converted git repository. Now we have to upload it to a repository hosting site, like say GitHub. GitHub has very good and detailed guides on how to setup your repositories, so I will just assume I signed up on the site as and tell you the commands you need in order to push the repository without going into much detail.

Create a set of SSH keys to be able to push your changes:

cd ~/.ssh
mkdir key_backup
cp id_rsa* key_backup
rm id_rsa*
ssh-keygen -t rsa -C ""

Copy the contents of your file (exactly as they are, without adding or removing anything) in your SSH Key management area and create a repository named gitprojectname using the web interface.

Before starting to commit and push things in your repository, you should configure the commit user of Git (the user and email that appears in the commit’s metadata). If you haven’t done so by now, you can set your system-wide git user like this:

git config --global ""
git config --global "John Doe"

If you prefer to use this user only for a particular repository:

cd ~/repository_conversion/gitprojectname
git config --local ""
git config --local "John Doe"

Finally, push your local repository to the remote site (you can also do this via SSH using the keyset you generated in the previous step and pointing to an URL that looks like

cd ~/repository_conversion/gitprojectname
git remote add origin
git push -u origin master

If you have several branches and want to upload them all you can try replacing the last step with git push --all.

Hope that was helpful.


Build latest ffmpeg from source

2012/01/11 1 comment

FFmpeg logoI use ffmpeg a lot in my work because I need to process lots of multimedia resources programmatically (without human intervention). The prebuilt binaries of ffmpeg usually suffice for your average encoding/decoding tasks (if due to your particular needs you lack certain propietary codecs you can always grab a more codec-rich build such as the one medibuntu offers). But sometimes you need advanced features such as filters (overlays,  scaling, padding…) and since filters are a constantly evolving feature it is interesting to know how to build ffmpeg from source.

Removing old stuff and solving dependencies

First, you need to install git (if you don’t already have it):

sudo apt-get install git

Next, uninstall any previous ffmpeg builds from your system (if you’re building ffmpeg with x264 support like I’m going to do, uninstall x264 as well):

sudo apt-get remove ffmpeg x264 libx264-dev
sudo apt-get autoremove

Now we need to install a bunch of dependencies. This list may vary depending on the ffmpeg configuration you want to use. Don’t worry too much if you forget about some codec or dependency at this point, ffmpeg will tell you if something’s missing in the configuration step.

In my case, I wanted as many codecs as I could remember available to ffmpeg so as you can see the dependency list is quite long:

sudo apt-get install build-essential git-core checkinstall yasm texi2html \
     libfaac-dev libjack-jackd2-dev libmp3lame-dev libopencore-amrnb-dev \
     libopencore-amrwb-dev libsdl1.2-dev libtheora-dev libva-dev libvdpau-dev \
     libvorbis-dev libvpx-dev libx11-dev libxfixes-dev libxvidcore-dev \
     zlib1g-dev librtmp-dev libgsm0710-dev libgsm0710mux-dev libgsm1-dev \
     libgsmme-dev libschroedinger-dev libspeechd-dev libspeex-dev \
     libspeexdsp-dev libspeex-ocaml-dev libdc1394-22-dev

Ok, if you read the dependency list (did you, really?) you’ll have noticed that x264 isn’t among the installed packages. The reason is that I’ll also be building x264 from source because the prebuilt binaries (I’m talking about the ones in Ubuntu’s repository) seem to be too old for the ffmpeg we’re about to build.

Building x264 as a shared library

First, clone x264‘s git repository to grab the latest version of the code. Then, use the –enable-shared flag when configuring to build it as a shared library, otherways ffmpeg won’t be able to use it.

git clone git://
cd x264
./configure --enable-shared
sudo make install

Optionally, you can use checkinstall to build a .deb package and thus make the binaries redistributable:

sudo checkinstall --pkgname=libx264 \
    --pkgversion="2:0.$(grep X264_BUILD x264.h -m1 | \
    cut -d' ' -f3).$(git rev-list HEAD | wc -l)+git$(git rev-list HEAD -n 1 | \
    head -c 7)" --backup=no --deldoc=yes \
    --fstrans=no --default

Well, now that we’ve got all the libraries we need it’s time to build our customized ffmpeg.

Building ffmpeg

Since  January 2011 ffmpeg no longer uses svn to host the code, you should keep this in mind when you read other ffmpeg tutorials (they may be outdated).

git clone git://
cd ffmpeg
./configure --enable-avfilter --enable-vdpau --enable-bzlib \
    --enable-libgsm --enable-libschroedinger --enable-libspeex \
    --enable-pthreads --enable-zlib --enable-libvpx \
    --disable-stripping --enable-runtime-cpudetect \
    --enable-vaapi --enable-swscale --enable-libdc1394 \
    --enable-shared --disable-static --enable-librtmp \
    --enable-gpl --enable-version3 --enable-nonfree \
    --enable-postproc --enable-libfaac --enable-libmp3lame \
    --enable-libopencore-amrnb --enable-libopencore-amrwb \
    --enable-libtheora --enable-libvorbis --enable-libx264 \
    --enable-libxvid --enable-x11grab --enable-filter=movie
sudo make install

Building ffmpeg takes quite some time, be patient. When everything’s done, call ffmpeg without parameters to see if it works.

In my case it didn’t, so I had to use strace to find out what was wrong.

Fixing runtime problems

sudo strace ffmpeg

Reveals the following:

access("/etc/", F_OK)      = -1 ENOENT (No such file or directory)
access("/etc/", R_OK)      = -1 ENOENT (No such file or directory)

It seems ffmpeg is trying to access two files that don’t exist. I’ll create them and see if that works.

sudo touch /etc/
sudo touch /etc/

And… that actually worked!

Now you have a fully functional customized ffmpeg build. Congratulations.

If you want to know more about the latest features and examples of ffmpeg filters, please check out the libavfilter documentation.