MediaElement.AudioStreamCount is 0 when playing karaoke songs which have multiple audio streams

When I play some karaoke songs, I try to switch audio stream, but I find the audio stream index is set to 0 and AudioStreamCount is 0. However, when I run the
ffprobe.exe -show_streams -select_streams a "@#$@.mpg"
I get two streams (See below). It seems that the audio streams info is not passed to MediaStreamSource. Is there a method allow me to set audio stream index? Thanks.

ffprobe version N-75474-g74e4948 Copyright (c) 2007-2015 the FFmpeg developers
built with gcc 4.9.3 (GCC)
configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-av
isynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enab
le-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --
enable-libdcadec --enable-libfreetype --enable-libgme --enable-libgsm --enable-l
ibilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enab
le-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --en
able-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --ena
ble-libtwolame --enable-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc
--enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enabl
e-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-lzma --ena
ble-decklink --enable-zlib
libavutil 55. 2.100 / 55. 2.100
libavcodec 57. 3.100 / 57. 3.100
libavformat 57. 2.100 / 57. 2.100
libavdevice 57. 0.100 / 57. 0.100
libavfilter 6. 6.100 / 6. 6.100
libswscale 4. 0.100 / 4. 0.100
libswresample 2. 0.100 / 2. 0.100
libpostproc 54. 0.100 / 54. 0.100
Input #0, mpeg, from '@#$@.mpg':
Duration: 00:03:49.78, start: 0.369778, bitrate: 6736 kb/s
Stream #0:0[0x1e0]: Video: mpeg2video (Main), yuv420p(tv, bt470bg), 720x576
[SAR 64:45 DAR 16:9], 6000 kb/s, 25 fps, 25 tbr, 90k tbn, 50 tbc
Stream #0:1[0x1c0]: Audio: mp2, 48000 Hz, stereo, s16p, 320 kb/s
Stream #0:2[0x1c1]: Audio: mp2, 48000 Hz, stereo, s16p, 320 kb/s
[STREAM]
index=1
codec_name=mp2
codec_long_name=MP2 (MPEG audio layer 2)
profile=unknown
codec_type=audio
codec_time_base=1/48000
codec_tag_string=[0][0][0][0]
codec_tag=0x0000
sample_fmt=s16p
sample_rate=48000
channels=2
channel_layout=stereo
bits_per_sample=0
id=0x1c0
r_frame_rate=0/0
avg_frame_rate=0/0
time_base=1/90000
start_pts=33280
start_time=0.369778
duration_ts=20615039
duration=229.055989
bit_rate=320000
max_bit_rate=N/A
bits_per_raw_sample=N/A
nb_frames=N/A
nb_read_frames=N/A
nb_read_packets=N/A
DISPOSITION:default=0
DISPOSITION:dub=0
DISPOSITION:original=0
DISPOSITION:comment=0
DISPOSITION:lyrics=0
DISPOSITION:karaoke=0
DISPOSITION:forced=0
DISPOSITION:hearing_impaired=0
DISPOSITION:visual_impaired=0
DISPOSITION:clean_effects=0
DISPOSITION:attached_pic=0
[/STREAM]
[STREAM]
index=2
codec_name=mp2
codec_long_name=MP2 (MPEG audio layer 2)
profile=unknown
codec_type=audio
codec_time_base=1/48000
codec_tag_string=[0][0][0][0]
codec_tag=0x0000
sample_fmt=s16p
sample_rate=48000
channels=2
channel_layout=stereo
bits_per_sample=0
id=0x1c1
r_frame_rate=0/0
avg_frame_rate=0/0
time_base=1/90000
start_pts=33280
start_time=0.369778
duration_ts=20679839
duration=229.775989
bit_rate=320000
max_bit_rate=N/A
bits_per_raw_sample=N/A
nb_frames=N/A
nb_read_frames=N/A
nb_read_packets=N/A
DISPOSITION:default=0
DISPOSITION:dub=0
DISPOSITION:original=0
DISPOSITION:comment=0
DISPOSITION:lyrics=0
DISPOSITION:karaoke=0
DISPOSITION:forced=0
DISPOSITION:hearing_impaired=0
DISPOSITION:visual_impaired=0
DISPOSITION:clean_effects=0
DISPOSITION:attached_pic=0
[/STREAM]

Start by reviewing how MediaStreamSource exposes streams to MediaElement, then reproduce the issue with the supplied ffprobe command and MPEG sample. Trace why the two audio streams are not reported through AudioStreamCount. Done means both streams are exposed and the audio stream index can be selected.