ffmpeg filter_complex concat does not include audio

Question

I've managed to put together an ffmpeg filter complex which:

1. Scales an FBI warning (fbi.mp4) to the size ($w:$h) of a training video (train.mp4).
2. Pads the FBI warning so it's centered.
3. Concats the FBI warning and training video together.
4. Stamps the content with a rotated watermark (image.png).

The following works on silent videos (*see version information for ffmpeg below):

ffmpeg -y -i fbi.mp4 -i train.mp4 -i $img -filter_complex "
[0:v]            scale=$w:-1                                 [fbi_sca];
[fbi_sca]        pad=$w:$h:($w-iw)/2:($h-ih)/2               [fbi_pad];
[fbi_pad][1:v]   concat=n=2:v=1                              [concat];
[2:v]            rotate=-PI/4:c=none:ow=rotw(iw):oh=roth(ih) [rotate];
[concat][rotate] overlay=(W-w)/2+110:(H-h)/2-90              [out]
" -map [out] -codec:a copy -c:v libx264 final.mp4

My questions are as follows:

Can someone rewrite the above command / filter_complex to:

1. Automatically get the width and height of the training video (train.mp4) without first having to probe it, parse it, and fill the variables $w and $h (it's okay if I have to do this in a separate step, but I'd prefer not to).

2. (More importantly) Account for both video and audio in the training video such that:

   a. The filter is agnostic about which streams, 1 or 0, the video and audio appear in.

   b. I can use the same complex for training videos that have no audio track only a video track.

   c. The train.mp4 audio begins in the right place in the concatenated output.

*FFMPEG VERSION:

$ ffmpeg -version  

ffmpeg version N-69568-g21051af Copyright (c) 2000-2015 the FFmpeg developers
built with gcc 4.9.2 (GCC)
configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-lzma --enable-decklink --enable-zlib
libavutil      54. 18.100 / 54. 18.100
libavcodec     56. 21.102 / 56. 21.102
libavformat    56. 19.100 / 56. 19.100
libavdevice    56.  4.100 / 56.  4.100
libavfilter     5.  9.103 /  5.  9.103
libswscale      3.  1.101 /  3.  1.101
libswresample   1.  1.100 /  1.  1.100
libpostproc    53.  3.100 / 53.  3.100

Answer 1

I also had the same issue, I have a way where I am able to append audio back to this filter,simply add

[0:a]aresample=44100;

It will resample audio at 44100 Hz(Change this value as per need) but Yes audio will now be there.Hope it helps.