[vlc-devel] Re: Commiting changes to svn ?

Gildas Bazin gbazin at altern.org
Sun Oct 3 16:22:52 CEST 2004

On Sunday 03 October 2004 15:58, Frédéric RUGET wrote:
> Hello,
> I have completed my "portaudio" audio_ouput module.
> (I have renamed it portaudio rather than asio because
> it should work with any portaudio implementation ;
> even if I have only tested it with portaudio/ASIO so far...).
> A few questions :
> 1. I would like to commit my changes to the svn repository
>     (OK, after release 0.8 is out :-).
>     Is it possible ?  What is the procedure ?

Just submit the new plugin to this mailing list with the required patch for 
the build system (you can use svn diff for this).
If your changes are all contained in the new plugin and don't touch any 
other VLC code than it is even possible it will be included before the 
0.8.0 release.

> 2. Audio/video synchronization
>     My implementation of the portaudio.c module is close to sdl.c :
>     in the portaudio's callback function, I just throw data at portaudio's
> face.
>     Magically though, when I play a DVD, sound and pictures are correctly
>     synchronized.  How is it possible ?

Luck maybe.
If you want precise synchronisation, you have to use aout_OutputNextBuffer() 
and not aout_FifoPop() like in the sdl plugin.

>     Small difference with sdl : the portaudio's callback function gives
>     (in addition to the samples buffer) a timestamp that tells the exact
> time
>     portaudio plans to output the buffer to the speakers.
>     Could I make use of this timestamp to achieve more precise audio/video
>     synchronization, or is it not compatible with VLC architecture ?

Sure, it is highly advised to do that. aout_OutputNextBuffer() takes a 
presentation date as a parameter so that synchronisation can be done.
But beware that this date is a VLC date so you might not be able to directly 
feed the portaudio date to VLC.

>     More generally, is there documentation about audio/video
>     synchonization in VLC ?

You should find some info in the developers doc (which is outdated but the 
audio section should still be relevant). 

> 3. What are the recommended compilation flags to optimize VLC
>      for speed ? (on WindowsXP/cynwin)

The default compilation flags should already be pretty good but you can have 
a look at gcc's manual if you want to find which flags you can use to 
optimize code for your specific processor (Even though I doubt you'll see a 


This is the vlc-devel mailing-list, see http://www.videolan.org/vlc/
To unsubscribe, please read http://developers.videolan.org/lists.html

More information about the vlc-devel mailing list