[Speex-dev] Little bug in the libspeexdsp resampler

[John Ridges]

Hi Jean-Marc,

I reported this bug a couple of months ago and either it got lost or I 
just didn't make my case very well. Let me see if I can explain why 
"speex_resampler_process_interleaved_int" and 
"speex_resampler_process_interleaved_float" in the resampler have a problem.

If you call "speex_resampler_process_interleaved_int" with a small 
"out_len" (and therefore is output limited), then the first time the 
function calls "speex_resampler_process_int", it changes "in_len" to the 
number of input samples it no longer needs to see again (I note that 
this is different than the number of samples it may have *used*). The 
problem is that for the second (and subsiquent) channels, while 
"out_len" is reset to the original value, "in_len" is not, and so it is 
possible that the subsiquent calls to "speex_resampler_process_int" 
could be *input* limited, which will make that channel produce a 
different number of output samples than the first channel. An example:

resampler set to an input rate of 8000 Hz, and an output rate of 16000 
Hz, and "speex_resampler_process_interleaved_int" is called with in_len 
= 1000000 and out_len = 101. This is what happens inside the function:

before first call to speex_resampler_process_int, in_len = 1000000, 
out_len = 101
after first call to speex_resampler_process_int, in_len = 50, out_len = 
101 (output limited)
out_len reset to 101 so -
before second call to speex_resampler_process_int, in_len = 50, out_len 
= 101
after second call to speex_resampler_process_int, in_len = 50, out_len = 
100 (input limited)

and so "speex_resampler_process_interleaved_int" returns an in_len = 50 
and out_len = 100, and I think the expectation of that function is that 
either it will change in_len or out_len, but not both.

--John Ridges