I have 3 amr-nb samples and one of them is played ok in audacious.
Two of them don't play.

----------- example 1 - NOT playing in audacious -------------------------

General
Complete name                            : example.amr
Format                                   : AMR
Format/Info                              : Adaptive Multi-Rate
File size                                : 3.54 KiB
Duration                                 : 5s 560ms
Overall bit rate mode                    : Constant
Overall bit rate                         : 5 200 bps

Audio
Format                                   : AMR
Format/Info                              : Adaptive Multi-Rate
Format profile                           : Narrow band
Duration                                 : 5s 560ms
Bit rate mode                            : Constant
Bit rate                                 : 5 200 bps
Channel(s)                               : 1 channel
Sampling rate                            : 8 000 Hz
Bit depth                                : 13 bits
Stream size                              : 3.53 KiB (100%)

----------- example 2 - NOT playing in audacious -------------------------

General
Complete name                            : example2.amr
Format                                   : AMR
Format/Info                              : Adaptive Multi-Rate
File size                                : 1.83 KiB
Duration                                 : 1s 782ms
Overall bit rate mode                    : Constant
Overall bit rate                         : 8 400 bps

Audio
Format                                   : AMR
Format/Info                              : Adaptive Multi-Rate
Format profile                           : Narrow band
Duration                                 : 1s 782ms
Bit rate mode                            : Constant
Bit rate                                 : 8 400 bps
Channel(s)                               : 1 channel
Sampling rate                            : 8 000 Hz
Bit depth                                : 13 bits
Stream size                              : 1.83 KiB (100%)

----------- example 3 - playing OK in audacious -------------------------

eneral
Complete name                            : example_works.amr
Format                                   : AMR
Format/Info                              : Adaptive Multi-Rate
File size                                : 23.9 KiB
Duration                                 : 30s 640ms
Overall bit rate mode                    : Constant
Overall bit rate                         : 6 400 bps

Audio
Format                                   : AMR
Format/Info                              : Adaptive Multi-Rate
Format profile                           : Narrow band
Duration                                 : 30s 640ms
Bit rate mode                            : Constant
Bit rate                                 : 6 400 bps
Channel(s)                               : 1 channel
Sampling rate                            : 8 000 Hz
Bit depth                                : 13 bits
Stream size                              : 23.9 KiB (100%)


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I do not see any significant differences between mediainfo output of these 3 samples