CVS Commit: vlc

Laurent Aimar fenrir at
Thu May 2 13:58:13 CEST 2002

On Thu, May 02, 2002, Jean-Paul Saman wrote:
> It does not solve the problem. I noticed the audio to be faster then it 
> should be (at least twice) when running with avi plugin. Which gives a 
> nice effect, Jean-Claude sounded just like Donald Duck :-).

 It's really strange, because i 'v just done 'cvs update' and 'make' and
for this file (only,for the other the sound the sound totally unusable)
if I set ADEC_FRAME_SIZE to 2*512 it work for me( audio is quite perfect
and video and audio are synchro all along the file ). Perhaps there is
another problem (perhaps because hardware is different).

> One of my own MPEG2 files sounds terrible with current CVS version. 
> While in vlc-0.3.1 stable versions it is OK. So my guess is that it is 
> not simple related to mad or avi plugin, there is more to it.

 I've look at mad source and i've see that for mpeg layer 3 the
length of pcm output ( in libmad_output it is p_libmad_pcm->length i
think ) is not a constant like for other layer. it's defined by 32 *
MAD_NSBSAMPLES(header) where

# define MAD_NSBSAMPLES(header)  \
  ((header)->layer == MAD_LAYER_I ? 12 :  \
   (((header)->layer == MAD_LAYER_III &&  \
     ((header)->flags & MAD_FLAG_LSF_EXT)) ? 18 : 36)
( and header is the header for a mpeg audio frame )

 So, In layer 3 there is two sort of frame : short(for transition, 576
samples ) and long(1152 samples). But if i am not wrong, this is not
supported in plugin mad for vlc.

 About other thing: for me mono audio always make vlc to segfault,
whereas builtin mpeg decoder have very bad sound but don't segfault. I
don't know if i am the only one who see that.

 About the way that i call the audio decoder by MPEG2_AUDIO_ES is
because i can't know what really it is (i know only the layer), (avi
file format sux), but even if i change it, it does nothing. Unless I 'm
wrong, mad plugin don't use it for decoding purpose but only to say if
it can decoded the stream, and it can do mpeg-I and II.

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