stretching files, unexpected duration after stretching file

Hello,

I use sox for converting and merging vox-files in a shell script. But 
the vox files often have different duration in seconds and I want to 
make sure that the shorter file always has the duration of the longer 
file before merging.

With soxi -D <file.vox> I get the length in seconds. If the differences 
between the two files are greater than 2 seconds, I calculate the 
stretch factor. The “problem” now is that the stretched file is often 
longer than the longer file itself, e.g.

soxi -D fileA.vox = 870.408000
soxi -D fileB.vox = 868.360000

stretch factor = 1.00235846883780920355

The used command for stretching is:

sox -r 8000 -t vox “$fileB” -r 8000 -t vox 
“${work_dir}/fileB_stretched.vox” stretch “$factor”

But the unexpected result of stretching this file is

soxi -D ${work_dir}/fileB_stretched.vox = 875.197500

I don't know how this inaccuracy is caused. Is there a way to stretch it 
more accurately?

chatgpt says that the cause of the deviation is probably due to the 
block sizes of the VOX format or rounding errors when calculating the 
sample length. A precise solution requires either post-processing of the 
stretched file (e.g. with trim) or the use of a lossless format such as 
WAV for intermediate processing. However, I achieved the same result 
with these files in WAV format and I dont want to use trim.

Any idea?


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