Opened 14 years ago

Closed 14 years ago

Last modified 14 years ago

#22 closed defect (fixed)

first argument in pan filter is number of INPUT channels, but not OUTPUT as stated in docs

Reported by: ace@… Owned by: diego@…
Priority: normal Component: DOCS
Version: HEAD Severity: normal
Keywords: Cc:
Blocked By: Blocking:
Reproduced by developer: Analyzed by developer:

Description

I'm trying to make 6 channel audio from ordinary stereo track with pan filter.
According to documentation I do such thing:

mplayer -ao alsa9:surround51 -af pan=6:1:0:0:1:1:0:0:1:0.5:0.5,sub -v -channels
6 movie.avi

Checking audio filter chain for 48000Hz/2ch/16bit -> 48000Hz/6ch/16bit...
[libaf] Adding filter pan
[pan] Pan level from channel 0 to channel 0 = 1.000000
[pan] Pan level from channel 1 to channel 0 = 0.000000
[pan] Pan level from channel 2 to channel 0 = 0.000000
[pan] Pan level from channel 3 to channel 0 = 1.000000
[pan] Pan level from channel 4 to channel 0 = 1.000000
[pan] Pan level from channel 5 to channel 0 = 0.000000
[pan] Pan level from channel 0 to channel 1 = 0.000000
[pan] Pan level from channel 1 to channel 1 = 1.000000
[pan] Pan level from channel 2 to channel 1 = 0.500000
[pan] Pan level from channel 3 to channel 1 = 0.500000
[libaf] Adding filter sub
[libaf] Adding filter format

But as we see signal routing is strange, not as I'm expecting. Then I try:

mplayer -ao alsa9:surround51 -af pan=2:1:0:0:1:1:0:0:1:0.5:0.5,sub -v -channels
6

Checking audio filter chain for 48000Hz/2ch/16bit -> 48000Hz/6ch/16bit...
[libaf] Adding filter pan
[pan] Pan level from channel 0 to channel 0 = 1.000000
[pan] Pan level from channel 1 to channel 0 = 0.000000
[pan] Pan level from channel 0 to channel 1 = 0.000000
[pan] Pan level from channel 1 to channel 1 = 1.000000
[pan] Pan level from channel 0 to channel 2 = 1.000000
[pan] Pan level from channel 1 to channel 2 = 0.000000
[pan] Pan level from channel 0 to channel 3 = 0.000000
[pan] Pan level from channel 1 to channel 3 = 1.000000
[pan] Pan level from channel 0 to channel 4 = 0.500000
[pan] Pan level from channel 1 to channel 4 = 0.500000
[libaf] Adding filter sub
[libaf] Adding filter format
[format] Changing sample format from 16bit little endian signed int to 32bit
little endian float
[libaf] Adding filter channels
[channels] Changing number of channels to 6


Exactly what I need. So, first number after pan filter is not a number of
output channels as stated in docs, but number of input channels.

So, I looked up in code (af_pan.c):
static int control(struct af_instance_s* af, int cmd, void* arg)
.....

while((*cp == ':') && (k < AF_NCH)){

sscanf(cp, ":%f%n" , &s->level[k][j], &n);
s->level[k][j] = clamp(s->level[k][j],0.0,1.0);
af_msg(AF_MSG_VERBOSE,"[pan] Pan level from channel %i to"

" channel %i = %f\n",j,k,s->level[k][j]);

cp =&cp[n];
j++;
if(j>=nch){

j = 0;
k++;

}

}

...

As we see j is used as second array index and increments up to nch which is
number of OUTPUT channels. Let's see play function:

.....

int nchi = c->nch; Number of input channels

.....

while(in < end){

for(j=0;j<ncho;j++){

register float x = 0.0;
register float* tin = in;
for(k=0;k<nchi;k++)

x += tin[k] * s->level[j][k];

out[j] = x;

}
out+= ncho;
in+= nchi;

}


Here k is used as second array index and increments up to nchi, which is
number od INPUT channels.

So, "nature" test with mplayer given above shows the same.

Change History (2)

comment:1 Changed 14 years ago by diego@…

  • Component changed from af to DOCS
  • Owner changed from alex@… to diego@…

I assume we need to update the docs for this. Taking.

comment:2 Changed 14 years ago by reimar

  • Resolution set to fixed
  • Status changed from new to closed

After this had me confused myself a few times, I corrected the documentation.

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