The VideoLAN Forums

Hello,
I just downloaded vlc 0.7.2 (for windows 2000).
Great !
Just there is still a problem with quicktime .mov videos from Kodak camera (mine is DX4530). VLC won't play the sound correctly (seem to be ulaw). It just make intermittent noise (I would say 2 scratch by sec). When the video is paused, the noise continue for about 1 or 2 seconds.

I have put the video (4Mo) as well as the messages for that video (that is H263/ulaw).
If it may help, I although put the messages for a video that is played OK. (This video is from a non-kodak camera and is .mov too, but seem to use MJPEG/araw).

Any idea?
I would be pleased to give more informations if needed.
Cheers,
--
Triff

Sorry for the bad links.
Here they are :

I have put the video (4Mo) as well as the messages for that video (that is H263/ulaw).
If it may help, I although put the messages for a video that is played OK. (This video is from a non-kodak camera and is .mov too, but seem to use MJPEG/araw).

--
Triff

In fact I don't really know if it''s a bug in VLC or in the kodack cameras.

The probleme is in the box moov/track/mdia/minf/stsd (sample description atom).
In that box we find the codec ('ulaw') and among other thing the sample size.

The QuickTime file format spec I have say :
"Sample size
A 16-bit integer that specifies the number of bits in each uncompressed sound sample. Set this field to 8 for 8-bit sound, and to 16 for 16-bit sound."

And in fact the video.mov from my camera have this field set to 16.

But in libmp4.c (L2169), we find
{ FOURCC_ulaw, MP4_ReadBox_sample_soun, MP4_FreeBox_sample_soun }

which imply after finding the codec 'ulaw' we use MP4_ReadBox_sample_soun the parse the box.

Then in MP4_ReadBox_sample_soun we find
MP4_GET2BYTES( p_box->data.p_sample_soun->i_samplesize );
which correspond to the sample size.

But this i_samplesize seems to be the _rel_ sample size (ie. compressed sample size in that case).
It seems to be used to calculate the size of the chunk (as sample number * sample size) to read and pass to the decoder (araw).
I didn't dug enougth to understand how it work, but the fact is a dump output of the araw decoder show that :
- the data decoded is twice as big as it should be
- parts of the data decoded are in fact video data.

I'm sure the problem is here because putting a
p_box->data.p_sample_soun->i_samplesize = 8;
just after the
MP4_GET2BYTES( p_box->data.p_sample_soun->i_samplesize );
solve the problem (for those videos ...)

But I don't know how to solve it properly, and I don't know how this "sample size" should really be interpreted.

Should I fill a bug report or anything ?

(By the way, another quick hack to solve this problem in a video is to put with a hex editor a 0x08 in place of the 0x10 23 bytes after 'ulaw'. Then VLC read it OK, and it doesn't disturb media player classic neither)

Anyway, I was astounded being able to compile VLC without problems. (just download mingw and copy/paste the example command line of the readme!).
Thank you for your great work and your very clear explanations
--
Triff

I have commited a workaround. (Basically just using samplesize 8 for alaw/ulaw, in mp4.c).
Thanks for the report.

Great !
Just tested it from svn source : work perfectly.
Thank you !
--
Triff

umm hi... i have the same problem with VLC 0.8.1:
the sound is messed up when i play the videos from my cam.
can you please tell me how to fix it....?
what you wrote is a bit confusing to me

and why dont they fix that
the sound was fine with earlier versions of vlc... only the full screen was messed up... and now its the sound *sigh*

thank you