[MPlayer-dev-eng] mencoder -oac copy does not work all the times.

Giacomo Comes comes at naic.edu
Mon Jan 17 17:45:09 CET 2005

I have found that -oac copy produces incorrect results
in some particular cases.

Here is a simple way to test the bug;
take a dvd with LPCM audio and do:

mencoder dvd://1 -ovc frameno -oac copy -aid 160 -frames 500 -o file.avi

Now play file.avi: mplayer file.avi

You will get only loud noise.

Explanation of the bug:

durning the copy mencoder stores in the avi header the format of the 
audio stream, the line of C code that does it in mencoder.c is:

mux_a->wf->wFormatTag = sh_audio->format

Now format, member of the structure sh_audio_t, is a unsigned int
but wFormatTag, member of the structure WAVEFORMATEX, is a unsigned short.

If the audio stream has a format that can be represented with 16 bit,
the result is correct:
0x50	(mp2)
0x55 	(mp3)
0x2000 	(ac3)
0x1 	(pcm)

If the audio stream has a format that requires more than 16 bit,
it cannot be stored correctly in the avi header.
0x10001	(dvdpcm) 
and all the other 32 bit format listed in codec.conf

I have prepared this small patch:

--- libmpdemux/ms_hdr.h.ori	2005-01-17 11:49:41.000000000 -0400
+++ libmpdemux/ms_hdr.h	2005-01-17 11:50:37.000000000 -0400
@@ -4,7 +4,7 @@
 typedef struct __attribute__((__packed__)) _WAVEFORMATEX {
-  unsigned short  wFormatTag;
+  unsigned int    wFormatTag;
   unsigned short  nChannels;
   unsigned int    nSamplesPerSec;
   unsigned int    nAvgBytesPerSec;

I did some tests and it seems to work. But I'm not sure if
it breaks something else.

Can anybody comment on this patch?

I have found a similar structure defined in loader/wine/mmreg.h
the following patch change wFormatTag as before, but I dont know
if this should be appliend or not, may be it is not necessary.

--- loader/wine/mmreg.h.ori	2005-01-17 12:30:33.000000000 -0400
+++ loader/wine/mmreg.h	2005-01-17 12:30:38.000000000 -0400
@@ -47,7 +47,7 @@
 typedef struct __attribute__((__packed__)) _WAVEFORMATEX {
-  WORD   wFormatTag;
+  DWORD  wFormatTag;
   WORD   nChannels;
   DWORD  nSamplesPerSec;
   DWORD  nAvgBytesPerSec;

I can prepare and submit a proprer patch if requested.


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