I have heard several people tell me that automatic segmentation and transcription to (narrow) IPA of fieldwork-quality audio is impossible at the moment, and even from laboratory-quality audio recordings for known languages it appears to be a hard and error-prone process.

I can comprehend that background noise, and speaker changes and other effects of recording in the field make the processing harder and that knowledge about the phonotactics of an existing language makes it easier to disambiguate possible options for sounds reflected in a recording.

But given that it is so easy to extract the formant shape from a waveform using standard software (eg. praat) and that formants seem to map to the vowel trapez so nicely; and also because clean transcription is a significant economic and time hurdle to research, I am surprised that this is such a big problem in practice.

What are the current big issues in automatic audio-to-IPA and what makes them so hard? Which bits are essentially solved?