Wess-iMac:~ wes$ ffmpeg -i "There Were Roses-original.mp4" -i "There Were Roses-9DKNs68Xo6Q.ac3" -map 0:v -map 1:a -codec copy "There Were Roses.mp4"
ffmpeg version 2.1 Copyright (c) 2000-2013 the FFmpeg developers
  built on Nov 11 2013 12:00:10 with llvm-gcc 4.2.1 (LLVM build 2336.11.00)
  configuration: --prefix=/Volumes/Ramdisk/sw --enable-gpl --enable-pthreads --enable-version3 --enable-libspeex --enable-libvpx --disable-decoder=libvpx --enable-libmp3lame --enable-libtheora --enable-libvorbis --enable-libx264 --enable-avfilter --enable-libopencore_amrwb --enable-libopencore_amrnb --enable-filters --enable-libgsm --arch=x86_64 --enable-runtime-cpudetect
  libavutil      52. 48.100 / 52. 48.100
  libavcodec     55. 39.100 / 55. 39.100
  libavformat    55. 19.104 / 55. 19.104
  libavdevice    55.  5.100 / 55.  5.100
  libavfilter     3. 90.100 /  3. 90.100
  libswscale      2.  5.101 /  2.  5.101
  libswresample   0. 17.104 /  0. 17.104
  libpostproc    52.  3.100 / 52.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'There Were Roses-original.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    creation_time   : 2015-03-17 12:15:14
  Duration: 00:04:31.88, start: 0.000000, bitrate: 2726 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 2532 kb/s, 30 fps, 30 tbr, 30 tbn, 60 tbc (default)
    Metadata:
      creation_time   : 1970-01-01 00:00:00
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 192 kb/s (default)
    Metadata:
      creation_time   : 2015-03-17 12:15:15
      handler_name    : IsoMedia File Produced by Google, 5-11-2011
[ac3 @ 0x7fc9b40d6800] Estimating duration from bitrate, this may be inaccurate
Input #1, ac3, from 'There Were Roses-9DKNs68Xo6Q.ac3':
  Duration: 00:04:31.92, start: 0.000000, bitrate: 191 kb/s
    Stream #1:0: Audio: ac3, 44100 Hz, stereo, fltp, 192 kb/s
File 'There Were Roses.mp4' already exists. Overwrite ? [y/N] y
[mp4 @ 0x7fc9b4808600] track 1: codec frame size is not set
Output #0, mp4, to 'There Were Roses.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    encoder         : Lavf55.19.104
    Stream #0:0(und): Video: h264 ([33][0][0][0] / 0x0021), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], q=2-31, 2532 kb/s, 30 fps, 15360 tbn, 30 tbc (default)
    Metadata:
      creation_time   : 1970-01-01 00:00:00
      handler_name    : VideoHandler
    Stream #0:1: Audio: ac3 ([165][0][0][0] / 0x00A5), 44100 Hz, stereo, 192 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #1:0 -> #0:1 (copy)
Press [q] to stop, [?] for help
frame= 8156 fps=4075 q=-1.0 Lsize=   90591kB time=00:04:31.86 bitrate=2729.7kbits/s
video:84043kB audio:6373kB subtitle:0 global headers:0kB muxing overhead 0.193268%
Wess-iMac:~ wes$