gst-av 0.4; better performance for flac, vorbis and mp3 (part 2)

This is a continuation of my previous post. Based on the feedback I decided to do two things; investigate the strange FLAC high CPU usage with FFmpeg, and get more accurate measurements.

GStreamer sucks

It turns out that GStreamer flac parser uses four times more CPU than FFmpeg’s decoder. Thanks to perf, I was able to quickly figure out the biggest offenders: GStreamer’s horrible bitstream reader (GST_BIT_READER_READ_BITS) was by far the worst.


This is on my laptop just running the parser (filesrc ! flacparse ! fakesink), in total it was taking 2.67s.

After reading the code and trying different things, I decided to go for something similar to what FFmpeg is doing, and I also borrowed pieces of the architecture-specific optimizations, now it even looks ok:


And it takes 0.81s.

But how much would this affect battery life on the N900?

Smart battery script

I tried different ideas, and after refreshing myself on statistics I wrote this script in Ruby that runs all the tests, gathers the battery capacity in a separate thread, and finally generates a report per test. Much easier than before.

Since I’m already working on FLAC, I decided to also apply some patches that split the decoder from the parser, and optimizations from Måns Rullgård (good thing I grabbed them because he seems to have left the project and deleted his repos).

Battery life graph

Battery life

Battery drain graph

Battery drain

So, yeah, much better now 😉

But how credible are these results? Well, judge by yourself, listed below are the raw measurements, the samples are the differences in capacity (mAh) measured each 10 minutes, from which the drain and battery life are calculated.

== baseline ==
samples: 3, 3, 3, 3, 4, 5
drain: 21.00±1.87mA
life: 65.39±4.77h
== av flac ==
samples: 9, 8, 8, 8, 7, 8, 7
drain: 47.14±1.45mA
life: 28.19±0.87h
== flac ==
samples: 11, 11, 11, 11, 11, 11
drain: 66.00±0.00mA
life: 20.00±0.00h
== av mp3 ==
samples: 11, 11, 11, 11, 11, 10
drain: 65.00±0.91mA
life: 20.33±0.30h
== nokiamp3 ==
samples: 12, 12, 12, 12, 12, 12
drain: 72.00±0.00mA
life: 18.33±0.00h
== av vorbis ==
samples: 10, 11, 11, 10, 11, 11
drain: 64.00±1.15mA
life: 20.67±0.38h
== vorbis ==
samples: 19, 18, 18, 19, 18, 19
drain: 111.00±1.22mA
life: 11.90±0.13h

If you are interested in the code: gst-av, gst-maemo-xiph. Enjoy 😉


Installing scratchbox 1 and 2 for ARM cross-compilation


I’ve tried many different cross-compilation methods and so far scratchbox is the simplest and most effective. Here I’ll try to introduce the benefits of using it, and how to get started as simply as possible.


If you are not familiar with scratchbox; it’s a cross-compilation toolkit which allows you to use native tools (gcc, binutils, perl) when possible and emulate the target through qemu when needed.

It’s needed because of autotools; have you seen these checks?
checking whether the C compiler works... yes

The configure script actually compiles a small program and then runs it to validate it’s working, and sometimes extract information, such a the size of certain structures which might be different depending on the platform. If you tell ‘configure’ that you are cross-compiling it will go through a different path (which is much less tested) and ultimately will end up with wrong information that you need to correct.

OpenEmbedded and other distributions go through each and every package, make sure cross-compilation works, sometimes patching, and often providing some information that normally would be obtained by running some test program.

This is an example of a typical GLib cross-compilation
./configure ---host=arm-linux --build=i386-linux

You’ll see something like:

checking whether the C compiler works... yes
checking whether we are cross compiling... yes

And then:

checking for growing stack pointer... configure: error: in `glib-2.20.3':
configure: error: cannot run test program while cross compiling

Of course, ‘configure’ has no way of knowing whether the stack grows on this particular platform. So you need to tell him yourself by creating an arm-linux.cache file like this:

And then running:
./configure --host=arm-linux --build=i386-linux --cache-file=arm-linux.cache

Of course that is not enough, you need to specify more:

And then the compilation fails because I don’t have glib-genmarshal in my system, and it’s needed by the build. Normally it’s compiled and run in the build, but now we can’t do that.

All these problems disappear with scratchbox.

Installing scratchbox 1

Many people think it’s difficult to install, but it’s not. Just follow these easy steps:


Download the basic packages:
wget -c
wget -c
wget -c
wget -c

Extract them:
sudo tar -xf /tmp/sb/scratchbox-core-1.0.14-i386.tar.gz -C /opt
sudo tar -xf /tmp/sb/scratchbox-libs-1.0.14-i386.tar.gz -C /opt
sudo tar -xf /tmp/sb/scratchbox-devkit-qemu-0.10.0-0sb5-i386.tar.gz -C /opt
sudo tar -xf /tmp/sb/scratchbox-toolchain-cs2007q3-glibc2.5-arm7-1.0.12-9-i386.tar.gz -C /opt

Setup scratchbox, and add your user:
sudo /opt/scratchbox/
sudo /opt/scratchbox/sbin/sbox_adduser $USER yes

You'll need to re-login to be in the sbox group and have proper permissions:
sudo su $USER


Finally, setup an armv7 target (you can have multiple targets inside scratchbox):
/opt/scratchbox/tools/bin/sb-conf setup armv7 --force --compiler="cs2007q3-glibc2.5-arm7" --devkits="qemu" --cputransp="qemu-arm-sb"
/opt/scratchbox/tools/bin/sb-conf select armv7
/opt/scratchbox/tools/bin/sb-conf install armv7 --clibrary --devkits --fakeroot --etc

That's it, you have scratchbox setup 🙂 I explicitly mentioned all the commands, but instead you can run this script that I wrote.


Before running scratchbox you'll need to do some steps as root:
echo 0 > /proc/sys/vm/vdso_enabled
echo 4096 > /proc/sys/vm/mmap_min_addr
/opt/scratchbox/sbin/sbox_ctl start

And then as user:

This will get you to this screen:

Welcome to Scratchbox, the cross-compilation toolkit!

Use 'sb-menu' to change your compilation target.
See /scratchbox/doc/ for documentation.

[sbox-armv7: ~] > 

Now if you want to cross-compile GLib, you do it as in your PC:
./configure && make install

Much easier, now scratchbox does all the magic 😉

Scratchbox 2

Scratchbox 1 serves it's purpose, but there are many corner-cases where things get overly complicated so people came up with a much more elegant approach: Scratchbox 2.

In sb1 you need to login to a target (e.g. armv7, armv6, fremantle, diablo, etc.) in order to do anything, you can use only one target at a time, and each target is independent, in order to share tools between targets you need a devkit. Also, toolchains must be packaged in a special way.

In sb2, you don't login, you can setup any toolchain easily, you can use multiple targets at the same time, and you can configure it to do pretty much anything you want.


sb2 doesn't include QEMU, you must have it already, this is how I compile it:
git clone git://
cd qemu
git checkout -b stable v0.10.5
./configure --prefix=/opt/qemu --target-list=arm-linux-user
make install


Compile and install like this:
git clone git://
cd sbox2
./configure --prefix=/opt/sb2
make install

Add sb2 to the PATH:
export PATH=/opt/sb2/bin:$PATH


Now it's time to configure a target, I have a CodeSourcery toolchain installed on /opt/arm-2008q3, so:
cd /opt/arm-2008q3/arm-none-linux-gnueabi/libc/
sb2-init -c /opt/qemu/bin/qemu-arm armv7 /opt/arm-2008q3/bin/arm-none-linux-gnueabi-gcc

You don't need to log-in, just prefix your commands with sb2 to do the magic:
sb2 ./configure --prefix=/opt/arm/

If you want to use a different target just use the -t option:
sb2 -t armv8 ./configure --prefix=/opt/arm/

How cool is that?

Android looks more than good

Anroid has been released:

Following last week’s announcement of the Open Handset Alliance, today we’re happy to offer an early look at the Android SDK. We’re eager to get feedback from lots of developers in our discussion group. We’re also providing developer documentation and this blog to help you get up and going.

It’s looking pretty good:

Here is a detailed explanation about the platform:

It looks like it has a lot of potential. They have just launched and they already have a very extensible platform, way beyond what we have in Maemo, and even in GNOME or any Linux DE. I give it a month before we have unbelievably-crazy, original and useful killer-applications.

I like to develop in Linux, with vim, in C or in Ruby, so I’m not so excited about their Eclipse based SDK, but I guess it makes it easier for a lot of people. I like Java, but I like to write stuff without any fancy IDE. Anyhow $25,000 looks like a pretty good motivation to try installing it 🙂

Two thumbs up.

More videos here.