[MEncoder-users] Using "-pan" for channel mixing

[Corey Hickey]

Tobias Brockamp wrote:
> Am 24.11.2007 um 21:57 schrieb Jan Knutar:
> 
>> On Saturday 24 November 2007 20:11, Tobias Brockamp wrote:
>>
>>> Anybody an idea how get out these "klicks"?
>> Reduce the total amount of volume, either by volume filter before  
>> pan or
>> by lowering the coefficients you feed to pan...
> 
> Hmm, but the volume isn't not so high.

You're using:
-af pan=2:1:0:0:1:1:0:0:1:0.5:0.5:1:1

..which is kind of a bare-bones, simple downmix. You could try lowering
the LFE volume:
-af pan=2:1:0:0:1:1:0:0:1:0.5:0.5:0.5:0.5

...or further:
-af pan=2:1:0:0:1:1:0:0:1:0.5:0.5:0.1:0.1

Beyond that, all I can say is that you're combining the sound output of
several channels and trying to make them fit in the volume range of a
single channel. In the first downmix listed above:

output_left = front_left + rear_left + center/2 + LFE

Let's say the possible range of audio sample values is from -1 to 1, and
plug in some sample numbers:

   1.6      =    0.7     +    0.4    +  0.6/2   + 0.2

As you can see, the output value is far out of range, even though the
input values aren't all particularly high.

Note that you can use -af pan=<whatever>,volume" to clip out-of-range
values without altering the output volume (when possible). Clipping
makes sound sound bad, though, so only use it as a last resort or if
only a small percentage of audio samples are expected to be out of range.

-Corey