ffmpeg -f lavfi -i color=color=black:size=1920x1080:rate=25 -f lavfi -i anullsrc=channel_layout=stereo:sample_rate=48000 -c:v prores_ks -profile:v 2 -vtag apcn -q:v 7 -pix_fmt yuv422p10le -c:a pcm_s16le -ar 48000 -vframes 2 -map 0:0 -map 1:0 -y output.mov

// output:

ffmpeg version N-76583-g3df9ec5 Copyright (c) 2000-2015 the FFmpeg developers
  built with gcc 5.2.1 (Ubuntu 5.2.1-22ubuntu2) 20151010
  configuration: --prefix=/home/ingest/dev/FFmpeg/build/ --pkg-config-flags=--static --extra-cf
lags=-I/home/ingest/dev/FFmpeg/build/include --extra-ldflags=-L/home/ingest/dev/FFmpeg/build/li
b --bindir=/home/ingest/bin --enable-gpl --enable-libass --enable-libfdk-aac --enable-libfreety
pe --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libvpx -
-enable-libx264 --enable-libx265 --enable-nonfree
  libavutil      55.  5.100 / 55.  5.100
  libavcodec     57. 15.100 / 57. 15.100
  libavformat    57. 14.100 / 57. 14.100
  libavdevice    57.  0.100 / 57.  0.100
  libavfilter     6. 15.100 /  6. 15.100
  libswscale      4.  0.100 /  4.  0.100
  libswresample   2.  0.101 /  2.  0.101
  libpostproc    54.  0.100 / 54.  0.100
Input #0, lavfi, from 'color=color=black:size=1920x1080:rate=25':
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: rawvideo (I420 / 0x30323449), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 25
 tbr, 25 tbn, 25 tbc
Input #1, lavfi, from 'anullsrc=channel_layout=stereo:sample_rate=48000':
  Duration: N/A, start: 0.000000, bitrate: 768 kb/s
    Stream #1:0: Audio: pcm_u8, 48000 Hz, stereo, u8, 768 kb/s
Output #0, mov, to 'output.mov':
  Metadata:
    encoder         : Lavf57.14.100
    Stream #0:0: Video: prores (prores_ks) (apcn / 0x6E637061), yuv422p10le, 1920x1080 [SAR 1:1
 DAR 16:9], q=2-31, 200 kb/s, 25 fps, 12800 tbn, 25 tbc
    Metadata:
      encoder         : Lavc57.15.100 prores_ks
    Stream #0:1: Audio: pcm_s16le (sowt / 0x74776F73), 48000 Hz, stereo, s16, 1536 kb/s
    Metadata:
      encoder         : Lavc57.15.100 pcm_s16le
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> prores (prores_ks))
  Stream #1:0 -> #0:1 (pcm_u8 (native) -> pcm_s16le (native))
Press [q] to stop, [?] for help
frame=    2 fps=0.0 q=-0.0 Lsize=      43kB time=00:00:00.08 bitrate=4389.4kbits/s
video:42kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.68180
1%

// the output is the same for any value of -vframes

// probing two frames (-vframes  2)

ffmpeg -i output.mov
ffmpeg version N-76583-g3df9ec5 Copyright (c) 2000-2015 the FFmpeg developers
  built with gcc 5.2.1 (Ubuntu 5.2.1-22ubuntu2) 20151010
  configuration: --prefix=/home/ingest/dev/FFmpeg/build/ --pkg-config-flags=--static --extra-cf
lags=-I/home/ingest/dev/FFmpeg/build/include --extra-ldflags=-L/home/ingest/dev/FFmpeg/build/li
b --bindir=/home/ingest/bin --enable-gpl --enable-libass --enable-libfdk-aac --enable-libfreety
pe --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libvpx -
-enable-libx264 --enable-libx265 --enable-nonfree
  libavutil      55.  5.100 / 55.  5.100
  libavcodec     57. 15.100 / 57. 15.100
  libavformat    57. 14.100 / 57. 14.100
  libavdevice    57.  0.100 / 57.  0.100
  libavfilter     6. 15.100 /  6. 15.100
  libswscale      4.  0.100 /  4.  0.100
  libswresample   2.  0.101 /  2.  0.101
  libpostproc    54.  0.100 / 54.  0.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'output.mov':
  Metadata:
    major_brand     : qt
    minor_version   : 512
    compatible_brands: qt
    encoder         : Lavf57.14.100
  Duration: 00:00:00.08, start: 0.000000, bitrate: 4389 kb/s
    Stream #0:0(eng): Video: prores (apcn / 0x6E637061), yuv422p10le, 1920x1080, 4316 kb/s, 25
fps, 25 tbr, 12800 tbn, 12800 tbc (default)
    Metadata:
      handler_name    : DataHandler
      encoder         : Lavc57.15.100 prores_ks

// note there are no audio tracks.

// probing a three frame file (-vframes 3)

ffmpeg -i output.mov
ffmpeg version N-76583-g3df9ec5 Copyright (c) 2000-2015 the FFmpeg developers
  built with gcc 5.2.1 (Ubuntu 5.2.1-22ubuntu2) 20151010
  configuration: --prefix=/home/ingest/dev/FFmpeg/build/ --pkg-config-flags=--static --extra-cf
lags=-I/home/ingest/dev/FFmpeg/build/include --extra-ldflags=-L/home/ingest/dev/FFmpeg/build/li
b --bindir=/home/ingest/bin --enable-gpl --enable-libass --enable-libfdk-aac --enable-libfreety
pe --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libvpx -
-enable-libx264 --enable-libx265 --enable-nonfree
  libavutil      55.  5.100 / 55.  5.100
  libavcodec     57. 15.100 / 57. 15.100
  libavformat    57. 14.100 / 57. 14.100
  libavdevice    57.  0.100 / 57.  0.100
  libavfilter     6. 15.100 /  6. 15.100
  libswscale      4.  0.100 /  4.  0.100
  libswresample   2.  0.101 /  2.  0.101
  libpostproc    54.  0.100 / 54.  0.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'output.mov':
  Metadata:
    major_brand     : qt
    minor_version   : 512
    compatible_brands: qt
    encoder         : Lavf57.14.100
  Duration: 00:00:00.12, start: 0.000000, bitrate: 5219 kb/s
    Stream #0:0(eng): Video: prores (apcn / 0x6E637061), yuv422p10le, 1920x1080, 4316 kb/s, 25
fps, 25 tbr, 12800 tbn, 12800 tbc (default)
    Metadata:
      handler_name    : DataHandler
      encoder         : Lavc57.15.100 prores_ks
    Stream #0:1(eng): Audio: pcm_s16le (sowt / 0x74776F73), 48000 Hz, stereo, s16, 1536 kb/s (d
efault)
    Metadata:
      handler_name    : DataHandler

// the audio tracks are here when -vframes > 2