user3138: I tried to add 2 .srt subtitles to a video, but the resulting file has only the first subtitle. This is the command I used:
ffmpeg -i $movie.mov -i $sub_en.srt -i $sub_de.srt \
-c:v copy -c:a copy \
-c:s:0 srt -metadata:s:s:0 language=eng \
-c:s:1 srt -metadata:s:s:1 language=ger \
$output.mkv

The full output below also shows it only encodes 1 subtitle (I replaced the long file names with the variables used above for clarity):
ffmpeg version 3.3.2-static http://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2017 the FFmpeg developers
  built with gcc 5.4.1 (Debian 5.4.1-11) 20170519
  configuration: --enable-gpl --enable-version3 --enable-static --disable-debug --disable-ffplay --disable-indev=sndio --disable-outdev=sndio --cc=gcc-5 --enable-fontconfig --enable-frei0r --enable-gnutls --enable-gray --enable-libass --enable-libfreetype --enable-libfribidi --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxvid --enable-libzimg
  libavutil      55. 58.100 / 55. 58.100
  libavcodec     57. 89.100 / 57. 89.100
  libavformat    57. 71.100 / 57. 71.100
  libavdevice    57.  6.100 / 57.  6.100
  libavfilter     6. 82.100 /  6. 82.100
  libswscale      4.  6.100 /  4.  6.100
  libswresample   2.  7.100 /  2.  7.100
  libpostproc    54.  5.100 / 54.  5.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '$movie.mov':
  Metadata:
    major_brand     : qt  
    minor_version   : 0
    compatible_brands: qt  
    creation_time   : 2017-08-23T15:33:19.000000Z
  Duration: 00:56:34.92, start: 0.000000, bitrate: 20807 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1920x1080 [SAR 1:1 DAR 16:9], 20546 kb/s, 25 fps, 25 tbr, 25 tbn, 50 tbc (default)
    Metadata:
      creation_time   : 2017-08-23T15:33:20.000000Z
      handler_name    : Core Media Data Handler
      encoder         : H.264
      timecode        : 01:00:00:00
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 255 kb/s (default)
    Metadata:
      creation_time   : 2017-08-23T15:33:20.000000Z
      handler_name    : Core Media Data Handler
    Stream #0:2(und): Data: none (tmcd / 0x64636D74) (default)
    Metadata:
      creation_time   : 2017-08-23T15:33:20.000000Z
      handler_name    : Core Media Data Handler
      timecode        : 01:00:00:00
Input #1, srt, from '$sub_en.srt':
  Duration: N/A, bitrate: N/A
    Stream #1:0: Subtitle: subrip
Input #2, srt, from '$sub_de.srt':
  Duration: N/A, bitrate: N/A
    Stream #2:0: Subtitle: subrip
Output #0, matroska, to '$output.mkv':
  Metadata:
    major_brand     : qt  
    minor_version   : 0
    compatible_brands: qt  
    encoder         : Lavf57.71.100
    Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 20546 kb/s, 25 fps, 25 tbr, 1k tbn, 25 tbc (default)
    Metadata:
      creation_time   : 2017-08-23T15:33:20.000000Z
      timecode        : 01:00:00:00
      handler_name    : Core Media Data Handler
      encoder         : H.264
    Stream #0:1(ger): Audio: aac (LC) ([255][0][0][0] / 0x00FF), 48000 Hz, stereo, fltp, 255 kb/s (default)
    Metadata:
      creation_time   : 2017-08-23T15:33:20.000000Z
      handler_name    : Core Media Data Handler
    Stream #0:2: Subtitle: subrip (srt)
    Metadata:
      encoder         : Lavc57.89.100 srt
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (copy)
  Stream #1:0 -> #0:2 (subrip (srt) -> subrip (srt))
Press [q] to stop, [?] for help
frame=20372 fps=236 q=-1.0 Lsize= 2091417kB time=00:13:35.78 bitrate=21001.7kbits/s speed=9.45x    
video:2065455kB audio:25494kB subtitle:8kB other streams:0kB global headers:0kB muxing overhead: 0.022014%
Exiting normally, received signal 2.

I know that in this particular case I can use mkvmerge, but it wouldn't work for .mp4 mov_text (.ttxt) subtitles, and anyway I would like to understand what is wrong with my ffmpeg command.

user1871: Whenever's there's multiple inputs fed to ffmpeg, and you need one more than video/audio/subtitle stream sent to the output, -map statements are needed.
ffmpeg -i $movie.mov -i $sub_en.srt -i $sub_de.srt \
-map 0:v -map 0:a -map 1 -map 2 \
-c:v copy -c:a copy -c:s srt \
-metadata:s:s:0 language=eng -metadata:s:s:1 language=ger \
$output.mkv

Since the subtitles are SRT, you can just do -c:s copy.

3138: <p>I tried to add 2 .srt subtitles to a video, but the resulting file has only the first subtitle. This is the command I used:</p>

<pre><code>ffmpeg -i $movie.mov -i $sub_en.srt -i $sub_de.srt \
-c:v copy -c:a copy \
-c:s:0 srt -metadata:s:s:0 language=eng \
-c:s:1 srt -metadata:s:s:1 language=ger \
$output.mkv
</code></pre>

<p>The full output below also shows it only encodes 1 subtitle (I replaced the long file names with the variables used above for clarity):</p>

<pre><code>ffmpeg version 3.3.2-static http://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2017 the FFmpeg developers
  built with gcc 5.4.1 (Debian 5.4.1-11) 20170519
  configuration: --enable-gpl --enable-version3 --enable-static --disable-debug --disable-ffplay --disable-indev=sndio --disable-outdev=sndio --cc=gcc-5 --enable-fontconfig --enable-frei0r --enable-gnutls --enable-gray --enable-libass --enable-libfreetype --enable-libfribidi --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxvid --enable-libzimg
  libavutil      55. 58.100 / 55. 58.100
  libavcodec     57. 89.100 / 57. 89.100
  libavformat    57. 71.100 / 57. 71.100
  libavdevice    57.  6.100 / 57.  6.100
  libavfilter     6. 82.100 /  6. 82.100
  libswscale      4.  6.100 /  4.  6.100
  libswresample   2.  7.100 /  2.  7.100
  libpostproc    54.  5.100 / 54.  5.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '$movie.mov':
  Metadata:
    major_brand     : qt  
    minor_version   : 0
    compatible_brands: qt  
    creation_time   : 2017-08-23T15:33:19.000000Z
  Duration: 00:56:34.92, start: 0.000000, bitrate: 20807 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1920x1080 [SAR 1:1 DAR 16:9], 20546 kb/s, 25 fps, 25 tbr, 25 tbn, 50 tbc (default)
    Metadata:
      creation_time   : 2017-08-23T15:33:20.000000Z
      handler_name    : Core Media Data Handler
      encoder         : H.264
      timecode        : 01:00:00:00
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 255 kb/s (default)
    Metadata:
      creation_time   : 2017-08-23T15:33:20.000000Z
      handler_name    : Core Media Data Handler
    Stream #0:2(und): Data: none (tmcd / 0x64636D74) (default)
    Metadata:
      creation_time   : 2017-08-23T15:33:20.000000Z
      handler_name    : Core Media Data Handler
      timecode        : 01:00:00:00
Input #1, srt, from '$sub_en.srt':
  Duration: N/A, bitrate: N/A
    Stream #1:0: Subtitle: subrip
Input #2, srt, from '$sub_de.srt':
  Duration: N/A, bitrate: N/A
    Stream #2:0: Subtitle: subrip
Output #0, matroska, to '$output.mkv':
  Metadata:
    major_brand     : qt  
    minor_version   : 0
    compatible_brands: qt  
    encoder         : Lavf57.71.100
    Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 20546 kb/s, 25 fps, 25 tbr, 1k tbn, 25 tbc (default)
    Metadata:
      creation_time   : 2017-08-23T15:33:20.000000Z
      timecode        : 01:00:00:00
      handler_name    : Core Media Data Handler
      encoder         : H.264
    Stream #0:1(ger): Audio: aac (LC) ([255][0][0][0] / 0x00FF), 48000 Hz, stereo, fltp, 255 kb/s (default)
    Metadata:
      creation_time   : 2017-08-23T15:33:20.000000Z
      handler_name    : Core Media Data Handler
    Stream #0:2: Subtitle: subrip (srt)
    Metadata:
      encoder         : Lavc57.89.100 srt
Stream mapping:
  Stream #0:0 -&gt; #0:0 (copy)
  Stream #0:1 -&gt; #0:1 (copy)
  Stream #1:0 -&gt; #0:2 (subrip (srt) -&gt; subrip (srt))
Press [q] to stop, [?] for help
frame=20372 fps=236 q=-1.0 Lsize= 2091417kB time=00:13:35.78 bitrate=21001.7kbits/s speed=9.45x    
video:2065455kB audio:25494kB subtitle:8kB other streams:0kB global headers:0kB muxing overhead: 0.022014%
Exiting normally, received signal 2.
</code></pre>

<p>I know that in this particular case I can use <code>mkvmerge</code>, but it wouldn't work for .mp4 mov_text (.ttxt) subtitles, and anyway I would like to understand what is wrong with my ffmpeg command.</p>
 1871: <p>Whenever's there's multiple inputs fed to ffmpeg, and you need one more than video/audio/subtitle stream sent to the output, <code>-map</code> statements are needed.</p>

<pre><code>ffmpeg -i $movie.mov -i $sub_en.srt -i $sub_de.srt \
-map 0:v -map 0:a -map 1 -map 2 \
-c:v copy -c:a copy -c:s srt \
-metadata:s:s:0 language=eng -metadata:s:s:1 language=ger \
$output.mkv
</code></pre>

<p>Since the subtitles are SRT, you can just do <code>-c:s copy</code>.</p>
