From your example.3gp, it states its properties as follows (using KMP Player):
C:\Documents and Settings\DEVELOPER\Desktop\example.3gp
General
Complete name : C:\Documents and Settings\DEVELOPER\Desktop\example.3gp
Format : MPEG-4
Format profile : 3GPP Media Release 4
Codec ID : 3gp4
File size : 5.23 KiB
Duration : 3s 460ms
Overall bit rate : 12.4 Kbps
Audio #1
ID : 1
Format : AMR
Format/Info : Adaptive Multi-Rate
Format profile : Narrow band
Codec ID : samr
Duration : 3s 460ms
Bit rate mode : Constant
Bit rate : 5 200 bps
Channel(s) : 1 channel
Sampling rate : 8 000 Hz
Resolution : 16 bits
Stream size : 2.20 KiB (42%)
Title : SoundHandle
Writing library :
You can use libVLC/VLC library via VLCJ which is supposed to be able to open any media format and containers. But, the problem is that GPL version of libVLC/VLC doesn't support AMR audio format used in 3GP container due to following statment (from Wikipedia):
To use AMR as audio codec, VLC and FFmpeg must be compiled with AMR
support. This is because the AMR license is not compatible with the
VLC license.
Moreover, when referring to this message http://mailman.videolan.org/pipermail/vlc-devel/2011-February/078807.html, it says:
In any case, parsing AMR is done by libavformat and libavcodec from
the FFmpeg project, not directly by the VideoLAN project.
Going through the message threads above, even if it is able to open AMR audio format via restricted version, it does have problem with AMR file seeking:
http://mailman.videolan.org/pipermail/vlc-devel/2011-February/078814.html