/Kretz/blog/

Friday, August 31. 2007

isch geh wech

Heute haben mich ein paar nette Leute gefragt, ob ich denn mal Rundmails verschicke... Naja, ich weiß nicht so recht... Da mir der Matthias schon immer gesagt hat, dass ich mal bloggen soll, blogge ich jetzt auch mal drauf los! (alsob ich so viel zu erzählen hätte), so dass alle, die was wissen wollen von mir, das auch selber nachlesen können!

Wobei ich mich natürlich über persönliche Emails freue und die auch sicherlich beantworte. Jedenfalls hab ich jetzt wirklich eine Kleinigkeit zu erzählen: ich gehe nach Sevilla für 6 Monate! Einerseits freue ich mich total, andererseits bin ich voll zerrissen und habe total Angst, dass ich die Zeit ohne Matthias gar nicht schaffe! Aber deswegen bin ich ja in Sevilla und nicht in Uruguay, wo man ja einfach mal (wenns gar nicht mehr geht und das Geld reicht) in den Flieger steigen kann und die Umwelt noch mehr mit CO2 vollhauen kann...was macht man nicht alles!?

Ich freue mich auf:

gutes Wetter, neue Umgebung, neue Herausforderungen, endlich mal richtig Spanisch lernen, neue Freunde, gutes Essen, Tapas, die spanische SMD (dort heißt sie GBU und besteht schon mal aus ca. 6 Leuten!)

und ich habe Angst vor:

der Zimmersuche, der Kälte im Zimmer ohne Heizung, den komischen Spaniern, die Frauen nicht in Ruhe lassen, und das Getrenntsein von Matthias

Posted by Flora in Auslandssemester at 00:42 | Comments (6) | Trackbacks (0)

Thursday, August 30. 2007

Phonon-Trolltech

It's been a month already since I was at the Trolltech office in Oslo, but ever since I wanted to write about it...

Trolltech invited me to be able to discuss the design of Phonon or, more in general, what their needs are for a multimedia API that they want to provide with or in addition to Qt. The first three days (Wed.-Fri.) we've been whiteboarding the whole day, which was quite exhausting but OTOH exactly what I always wished to be able to do when I was designing Phonon in the beginning. The outcome was that we agreed that we want to have an API that provides all the flexibility of a graph based approach while simplifying the concepts as good as possible so that non-experts have no trouble using the API for simple tasks without getting any details wrong.

Before

This is where we needed a small change in the Phonon frontend API to make this possible. Before August Phonon allowed "graphs" of the form:

Path changes

Now the AudioPath and VideoPath objects are replaced by a value based class called Path, which is hidden for simple cases: vs. or in code:

MediaObject *media = new MediaObject;
AudioPath *path = new AudioPath;
AudioOutput *output = new AudioOutput(Phonon::MusicCategory);
media->addAudioPath(path);
path->addOutput(output);

vs.

MediaObject *media = new MediaObject;
AudioOutput *output = new AudioOutput(Phonon::MusicCategory);
/*Path path =*/ Phonon::createPath(media, output);

I wanted to keep the Path concept to make it easier to support the most common "graph reconnection": to insert/remove effects. With the common graph you'd have to disconnect media and output, connect media to effect, and effect to output and also somehow tell the objects that they should not lose any signal data while they're still disconnected and that playback needs to continue seemlessly after the effect insertion. With the path object it's a simple

/*Effect *effect =*/ path.insertEffect(effectDescription);

Mixing

Another change is that is not allowed anymore. The implicit mixing of audio data is removed. (For video it was never allowed anyway). The plan is to add a special class that handles mixing after the 4.0 release. Implementation note: This is close to impossible to implement using libxine.

What's the gain?

Perhaps you've already seen it, but why is this now more flexible than what Phonon provided before? The answer is that you can now define arbitrary graphs like . In a later version we also want to have an object that can "contain" multiple MediaObjects in order to be able to control them in sync. This is basically the concept of a media graph containing multiple source nodes. But if you have only one source, which is the case for most apps, the MediaObject defines the graph implicitly. This hides the graph concept for most developers using Phonon, which IMO helps to make Phonon easier to use.

Trolltech

Now what's Trolltech's role with regard to Phonon? They want to provide multimedia API with Qt 4.4. And they decided to set their bets on Phonon. This means they will work (with me and the rest of the community that is interested) on continuing the design of the frontend API to support use cases like capture, transcoding, VoIP apps, Video chat, ... And they will work on backends for Windows, MacOS X and Linux (including embedded). KDE will ship the xine backend with 4.0, but that one has several problems:

libxine is GPL-only, so they cannot tell commercial customers to simply use Phonon on Linux for multimedia
libxine does not support mixing of audio streams, and I tried to separate the clock and ticket system in libxine to make it more flexible, but I feel like this is a dead end. libxine is designed for simple playback tasks and that's it.
no capture or encoding with libxine

For 4.0 it's still the best lib to use so I'll stick with it till then.

On another note, 2h per workday, while I'm working on Phonon, are now sponsored by Trolltech. This additional money is very welcome, especially now that we'll have to pay the rent for a flat in Heidelberg and another one in Sevilla.

Posted by Matthias Kretz in Phonon at 16:39 | Comments (10) | Trackbacks (0)

Sevilla

I'll be gone for 10 days to visit Sevilla, Spain. My wife will spend a semester abroad (and I'll stay in Heidelberg) at the University of Sevilla.

As finding a place to stay is not as organized as in most other (european) countries, the first task we'll have to accomplish is finding a flat that is not overpriced and not "interior" (meaning without windows). Until then we'll stay at a hostel and hope to also find time to do a bit of vacation.

The weather is supposed to be too hot for my taste, but just right for Flora.

I'll not be reading mailinglists, but if you send a mail directly to my address you have a small chance that I will see (and perhaps answer) it before Sept. 11th.

Posted by Matthias Kretz in personal at 15:07 | Comments (8) | Trackbacks (0)