Reason for sox mix restriction to two or more input files?

Reason for sox mix restriction to two or more input files?

[Dr. Thomas Tensi]

Dear all,


I am using sox for automatic, scripted file generation.

One step is a mix of several input files.  It may happen
that - by configuration - only a single input file remains
for that mixing step.

This cannot be handled by sox, because sox _requires_
at least two input files and quits with the message
   "Not enough input filenames specified"

I understand that at least one input file is necessary
(for finding the target length, sample rate etc.), but
why does sox fail when mixing a single input file?


          Best regards,

                   Thomas


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Re: Reason for sox mix restriction to two or more input files?

[Jeremy Nicoll - ml sox users]

On 2019-08-09 20:42, Dr. Thomas Tensi wrote:
> Dear all,
> 
> 
> I am using sox for automatic, scripted file generation.
> 
> One step is a mix of several input files.  It may happen
> that - by configuration - only a single input file remains
> for that mixing step.
> 
> This cannot be handled by sox, because sox _requires_
> at least two input files and quits with the message
>   "Not enough input filenames specified"
> 
> I understand that at least one input file is necessary
> (for finding the target length, sample rate etc.), but
> why does sox fail when mixing a single input file?

Probably because it's simpler to write programmes that assume
the user means what they say.  So if you ask sox to mix several
files, it is written assuming that you will provide more than
one.

You say you're using a script to drive this.  That means you are
in control.  Your script can - surely - determine that there's
only one input file and adjust the sox command(s) you're using
accordingly.


-- 
Jeremy Nicoll - my opinions are my own


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Re: Reason for sox mix restriction to two or more input files?

[Dr. Thomas Tensi]

Hello Jeremy,


thanks for the explanation!

You wrote:
 > > [sox requires at least two input files for mixing]
 > > I understand that at least one input file is necessary
 > > (for finding the target length, sample rate etc.), but
 > > why does sox fail when mixing a single input file?
 > Probably because it's simpler to write programmes that
 > assume the user means what they say.  So if you ask sox to
 > mix several files, it is written assuming that you will
 > provide more than one.

Hmm, I am not convinced yet.  When I use my analog mixing
desk, I can easily "mix" even one input to the master.  So
mixing should even be possible for one file.

When using sox manually I am fine with changing my command
line accordingly; for an automatic use of a command line
tool boundary cases should just work if there is a
reasonable interpretation.

So
     sox -m -v 0.3 inputfile outputfile
is just equivalent to
     sox -v 0.3 inputfile outputfile

 > You say you're using a script to drive this.  That means
 > you are in control.  Your script can - surely - determine
 > that there's only one input file and adjust the sox
 > command(s) you're using accordingly.

It is a bit more complicated than that, because the script
does not know at all about sox, but is configurable for
arbitrary command-line audio processors.  Unfortunately
the configuration now has to take care of a special case for
single file mixing in sox, where other audio processors
(like e.g. ecasound) have no problem at all.

Nevertheless I found a workaround: I always add a null file
as an input partner for all mixing steps.  This is ugly, but
it works.


         Best regards,

                 Thomas


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Re: Reason for sox mix restriction to two or more input files?

[Måns Rullgård]

Jeremy Nicoll - ml sox users <jn.ml.sxu.88@wingsandbeaks.org.uk> writes:

> On 2019-08-09 20:42, Dr. Thomas Tensi wrote:
>> Dear all,
>>
>>
>> I am using sox for automatic, scripted file generation.
>>
>> One step is a mix of several input files.  It may happen
>> that - by configuration - only a single input file remains
>> for that mixing step.
>>
>> This cannot be handled by sox, because sox _requires_
>> at least two input files and quits with the message
>>   "Not enough input filenames specified"
>>
>> I understand that at least one input file is necessary
>> (for finding the target length, sample rate etc.), but
>> why does sox fail when mixing a single input file?
>
> Probably because it's simpler to write programmes that assume
> the user means what they say.  So if you ask sox to mix several
> files, it is written assuming that you will provide more than
> one.

There doesn't seem to be any good reason for this.  The below patch
removes the restriction and doesn't seem to break anything based on a
quick test.

diff --git a/src/sox.c b/src/sox.c
index 0b103e269092..39533bac831d 100644
--- a/src/sox.c
+++ b/src/sox.c
@@ -2924,7 +2924,7 @@ int main(int argc, char **argv)
     combine_method = sox_concatenate;
 
   /* Make sure we got at least the required # of input filenames */
-  if (input_count < (size_t)(is_serial(combine_method) ? 1 : 2))
+  if (input_count < 1)
     usage("Not enough input filenames specified");
 
   /* Check for misplaced input/output-specific options */


-- 
Måns Rullgård


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Re: Reason for sox mix restriction to two or more input files?

[Dr. Thomas Tensi]

Hello Måns,


thanks for your effort!

I have the same opinion: mixing should be possible for
a single input.

Nevertheless be careful with your patch: one has to
check whether other operations (like multiply) are
still meaningful for a single input.  I think so,
but I have not looked deeply into that.


        Best regards,

                 Thomas



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Re: Reason for sox mix restriction to two or more input files?

[Måns Rullgård]

"Dr. Thomas Tensi" <t.tensi@gmx.de> writes:

> Hello Måns,
>
> thanks for your effort!
>
> I have the same opinion: mixing should be possible for
> a single input.
>
> Nevertheless be careful with your patch: one has to
> check whether other operations (like multiply) are
> still meaningful for a single input.  I think so,
> but I have not looked deeply into that.

I tested the merge, mix, and multiply options with a single input, and
it came out unchanged.  Seems like reasonable behaviour to me.

-- 
Måns Rullgård


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