Audio missing from some vob files

When streaming ripped DVDs to Mezzmo on a Roku Ultra I am not getting audio on some of them. Even when playing a single episode from a DVD, part of it may have audio while another part does not. The original DVD has audio and the DVD plays fine on a PC. On Mezzmo, the audio may drop out even within a single vob file. That is, part of a single .vob file may have audio while another part of that same .vob file may not. However the audio drop off seems to occur only at chapter boundaries, not randomly within a chapter.

Also, despite my file having 3 audio tracks, I can find no way to switch to an alternative audio track. When I go to the options screen on the Roku, the "default" audio track is selected and grayed out so it cannot be changed. How can I switch to an alternative track to see if that has audio? Here is the FFmpeg information from an episode that has a mixture of audio and no audio, and following that is another episode from the same disk that has audio all the way through. As far as I can tell, they are identical except for the information about each episode (there are only 2 episodes on this DVD):

ffmpeg version N-78742-gf477849 Copyright (c) 2000-2017 the FFmpeg developers
built with gcc 4.9.2 (GCC)
configuration: --arch=x86_64 --target-os=mingw32 --cross-prefix=x86_64-w64-mingw32- --enable-static --disable-shared --enable-zlib --disable-postproc --prefix=/home/peter/ffmpeg/build/gpl64 --enable-libmp3lame --enable-libx264 --enable-gpl --extra-libs='-lx264 -lpthread -lstdc++' --enable-runtime-cpudetect --extra-cflags=-I/home/peter/cc32/include --extra-ldflags=-L/home/peter/cc64/lib --pkg-config=pkg-config --pkg-config-flags=--static --disable-w32threads --enable-libvpx --enable-libvorbis --enable-libtheora --enable-libx265 --enable-cuda --enable-cuvid --enable-dxva2 --enable-libmfx --enable-nvenc --enable-gnutls --extra-libs='-lz -lnettle -lhogweed -lgmp -lidn -lws2_32 -lcrypt32'
libavutil 55. 74.100 / 55. 74.100
libavcodec 57.103.100 / 57.103.100
libavformat 57. 76.100 / 57. 76.100
libavdevice 57. 7.100 / 57. 7.100
libavfilter 6.100.100 / 6.100.100
libswscale 4. 7.102 / 4. 7.102
libswresample 2. 8.100 / 2. 8.100
Input #0, mpeg, from 'pipe:':
Duration: N/A, start: 0.060000, bitrate: N/A
Stream #0:0[0x1bf]: Data: dvd_nav_packet
Stream #0:1[0x1e0]: Video: mpeg2video (Main), yuv420p(tv, smpte170m, top first), 720x480 [SAR 8:9 DAR 4:3], Closed Captions, 29.97 fps, 59.94 tbr, 90k tbn, 59.94 tbc
Stream #0:2[0x82]: Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s
Stream #0:3[0x81]: Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s
Stream #0:4[0x80]: Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s
At least one output file must be specified
<MEZZMO>: Child process ended with code: 109, ExitCode=1
---> DB Level Info: 8, 4
---> Frame rate: 29.97
---> Aspect ratio: 4:3 PAR=8:9
---> Duration: 01:11:46 (multi-file total)
---> List: #dv;1:3;3325997056:6778320896;4306|\\192.168.1.129 \Library\DSVideo TV\Civil War A Film by Ken Burns, The (1990)\Civil War by Ken Burns, The (disc 4) [DVD]\vts_01_1.vob|\\192.168.1.129\Library\DSVideo TV\Civil War A Film by Ken Burns, The (1990)\Civil War by Ken Burns, The (disc 4) [DVD]\vts_01_2.vob|\\192.168.1.129\Library\DSVideo TV\Civil War A Film by Ken Burns, The (1990)\Civil War by Ken Burns, The (disc 4) [DVD]\vts_01_3.vob|\\192.168.1.129\Library\DSVideo TV\Civil War A Film by Ken Burns, The (1990)\Civil War by Ken Burns, The (disc 4) [DVD]\vts_01_4.vob|\\192.168.1.129\Library\DSVideo TV\Civil War A Film by Ken Burns, The (1990)\Civil War by Ken Burns, The (disc 4) [DVD]\vts_01_5.vob|\\192.168.1.129\Library\DSVideo TV\Civil War A Film by Ken Burns, The (1990)\Civil War by Ken Burns, The (disc 4) [DVD]\vts_01_6.vob|\\192.168.1.129\Library\DSVideo TV\Civil War A Film by Ken Burns, The (1990)\Civil War by Ken Burns, The (disc 4) [DVD]\vts_01_7.vob|\\192.168.1.129\Library\DSVideo TV\Civil War A Film by Ken Burns, The (1990)\Civil War by Ken Burns, The (disc 4) [DVD]\vts_01_8.vob

ffmpeg version N-78742-gf477849 Copyright (c) 2000-2017 the FFmpeg developers
built with gcc 4.9.2 (GCC)
configuration: --arch=x86_64 --target-os=mingw32 --cross-prefix=x86_64-w64-mingw32- --enable-static --disable-shared --enable-zlib --disable-postproc --prefix=/home/peter/ffmpeg/build/gpl64 --enable-libmp3lame --enable-libx264 --enable-gpl --extra-libs='-lx264 -lpthread -lstdc++' --enable-runtime-cpudetect --extra-cflags=-I/home/peter/cc32/include --extra-ldflags=-L/home/peter/cc64/lib --pkg-config=pkg-config --pkg-config-flags=--static --disable-w32threads --enable-libvpx --enable-libvorbis --enable-libtheora --enable-libx265 --enable-cuda --enable-cuvid --enable-dxva2 --enable-libmfx --enable-nvenc --enable-gnutls --extra-libs='-lz -lnettle -lhogweed -lgmp -lidn -lws2_32 -lcrypt32'
libavutil 55. 74.100 / 55. 74.100
libavcodec 57.103.100 / 57.103.100
libavformat 57. 76.100 / 57. 76.100
libavdevice 57. 7.100 / 57. 7.100
libavfilter 6.100.100 / 6.100.100
libswscale 4. 7.102 / 4. 7.102
libswresample 2. 8.100 / 2. 8.100
Input #0, mpeg, from 'pipe:':
Duration: N/A, start: 0.060000, bitrate: N/A
Stream #0:0[0x1bf]: Data: dvd_nav_packet
Stream #0:1[0x1e0]: Video: mpeg2video (Main), yuv420p(tv, smpte170m, top first), 720x480 [SAR 8:9 DAR 4:3], Closed Captions, 29.92 fps, 59.94 tbr, 90k tbn, 59.94 tbc
Stream #0:2[0x82]: Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s
Stream #0:3[0x81]: Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s
Stream #0:4[0x80]: Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s
At least one output file must be specified
<MEZZMO>: Child process ended with code: 109, ExitCode=1
---> DB Level Info: 8, 4
---> Frame rate: 29.92
---> Aspect ratio: 4:3 PAR=8:9
---> Duration: 01:09:14 (multi-file total)
---> List: #dv;2:3;0:3325995008;4154|\\192.168.1.129\Library\ DSVideo TV\Civil War A Film by Ken Burns, The (1990)\Civil War by Ken Burns, The (disc 4) [DVD]\vts_01_1.vob|\\192.168.1.129\Library\DSVideo TV\Civil War A Film by Ken Burns, The (1990)\Civil War by Ken Burns, The (disc 4) [DVD]\vts_01_2.vob|\\192.168.1.129\Library\DSVideo TV\Civil War A Film by Ken Burns, The (1990)\Civil War by Ken Burns, The (disc 4) [DVD]\vts_01_3.vob|\\192.168.1.129\Library\DSVideo TV\Civil War A Film by Ken Burns, The (1990)\Civil War by Ken Burns, The (disc 4) [DVD]\vts_01_4.vob|\\192.168.1.129\Library\DSVideo TV\Civil War A Film by Ken Burns, The (1990)\Civil War by Ken Burns, The (disc 4) [DVD]\vts_01_5.vob|\\192.168.1.129\Library\DSVideo TV\Civil War A Film by Ken Burns, The (1990)\Civil War by Ken Burns, The (disc 4) [DVD]\vts_01_6.vob|\\192.168.1.129\Library\DSVideo TV\Civil War A Film by Ken Burns, The (1990)\Civil War by Ken Burns, The (disc 4) [DVD]\vts_01_7.vob|\\192.168.1.129\Library\DSVideo TV\Civil War A Film by Ken Burns, The (1990)\Civil War by Ken Burns, The (disc 4) [DVD]\vts_01_8.vob

OK, so after a bit more experimentation I have a workaround. It doesn't explain why the audio from one disc from the set should play fine and others not, nor why one disc would play fine for one chapter and then not on the same disc, but by doing the following I got the audio to play.

1. I selected a different audio track in the video file properties using the Mezzmo app in Windows.
2. Then I pre-transcoded the files specifically for the Roku, overwriting any previous transcoding, and ticking the box to transcode even if the file matched a natively supported format.

I don't know if all those steps are necessary to get the result, but doing them all resulted in the audio playing.

For the Roku Mezzmo will transcode an mpeg file and select the first audio track by default, this works fine for most discs but some have the main audio as the second or third track which could result in problems. Selecting the audio in properties as you have done is the correct approach to get your audio to play.