Python implementation of MFCC algorithm
Run
mfcc_feat.shape
You should get (4831,13) . 13 is your MFCC length (default numcep is 13). 4831 is the windows. Default winstep is 10 msec, and this matches your sound file duration. To get to the windows corresponding to 19-29 sec, just slice
mfcc_feat[1900:2900,:]
Remember, that you can not listen to the MFCC. It just represents the slice of audio of 0.025 sec (default value of winlen parameter).
If you want to get to the audio itself, it is
sig[time_beg_in_sec*rate:time_end_in_sec*rate]