Mediacoder converting MKV to AVI with MP3 no sound

I have been using Mediacoder for several years with good results but recently I am having problems with MKV file conversions to AVI format. Sometimes the audio is out of sync and I have to adjust delay to correct it. Other times there is no audio when playing the converted video.

Here are the specs for the incoming MKV file:

General
Unique ID : 0 (0x0)
Complete name : V:\F Drive Videos\Temporary Work\Test.mkv
Format : Matroska
Format version : Version 4 / Version 2
File size : 799 MiB
Duration : 50 min 51 s
Overall bit rate : 2 198 kb/s
Encoded date : UTC 2010-02-22 21:41:29
Writing application : no_variable_data
Writing library : no_variable_data

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4.1
Format settings, CABAC : Yes
Format settings, RefFrames : 5 frames
Codec ID : V_MPEG4/ISO/AVC
Duration : 50 min 51 s
Width : 1 280 pixels
Height : 720 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 25.000 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Writing library : x264 core 150 r2833 df79067
Encoding settings : cabac=1 / ref=5 / deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=8 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=2 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=12 / lookahead_threads=2 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=3 / weightb=1 / open_gop=0 / weightp=2 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=50 / rc=crf / mbtree=1 / crf=18.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
Language : English
Default : Yes
Forced : No
Color range : Limited
Matrix coefficients : BT.709

Audio
ID : 2
Format : AAC
Format/Info : Advanced Audio Codec
Format profile : LC
Codec ID : A_AAC
Duration : 50 min 51 s
Channel(s) : 6 channels
Channel positions : Front: L C R, Side: L R, LFE
Sampling rate : 48.0 kHz
Frame rate : 46.875 FPS (1024 SPF)
Compression mode : Lossy
Default : Yes
Forced : No

Here are the specs from the converted AVI file:

General
Complete name : M:\Converted to AVI\MediaCoder\Test.avi
Format : AVI
Format/Info : Audio Video Interleave
File size : 742 MiB
Duration : 2 h 32 min
Overall bit rate : 680 kb/s
Writing application : Lavf55.33.100

Video
ID : 0
Format : MPEG-4 Visual
Format profile : Simple@L3
Format settings, BVOP : No
Format settings, QPel : No
Format settings, GMC : No warppoints
Format settings, Matrix : Default (H.263)
Codec ID : XVID
Codec ID/Hint : XviD
Duration : 50 min 51 s
Bit rate : 1 914 kb/s
Width : 1 280 pixels
Height : 720 pixels
Display aspect ratio : 16:9
Frame rate : 25.000 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Compression mode : Lossy
Bits/(Pixel*Frame) : 0.083
Stream size : 696 MiB (94%)
Writing library : XviD 67

Audio
ID : 1
Format : MPEG Audio
Format version : Version 1
Format profile : Layer 3
Mode : Joint stereo
Mode extension : MS Stereo
Codec ID : 55
Codec ID/Hint : MP3
Duration : 2 h 32 min
Bit rate mode : Constant
Bit rate : 32.0 kb/s
Channel(s) : 2 channels
Sampling rate : 48.0 kHz
Compression mode : Lossy
Stream size : 34.9 MiB (5%)
Alignment : Aligned on interleaves
Interleave, duration : 8 ms (0.20 video frame)
Interleave, preload duratio : 24 ms
Writing library : LAME3.99.5

Any suggestions as to why this is happening sometimes but not all the time?

Thanks in advance for any suggestions.

There is nothing obviously wrong. You might compare one file that gave problems to one that didn’t and see if you can spot differences in the way they are encoded.