title: Screen capture WITH audio in ffmpeg
body: <p>I am using ffmpeg built from source at <a href="https://github.com/FFmpeg/FFmpeg/commit/a66dcfeedc68c080965cf78e1e0694967acef5af" rel="noreferrer">this revision</a> in Fedora 20.</p>
  
  <p>I am able to record audio <strong>perfectly fine</strong> with the command:</p>
  
  <pre><code>FFmpeg/ffmpeg -f alsa -ac 2 -i pulse -- output.wav
  </code></pre>
  
  <p>However, when I try both screen capture and audio, like this:</p>
  
  <pre><code>FFmpeg/ffmpeg -video_size 800x600 -framerate 25 -ac 2 -f x11grab -i :0.0+0,0 -ac 2 -f alsa -i pulse -ac 2 -acodec copy output.mpeg -ac 2
  </code></pre>
  
  <p>I'm getting a video with 0 audio channels, which I can check running <code>FFmpeg/ffplay output.mpeg</code></p>
  
  <pre><code>Input #0, mpeg, from 'output.mpeg':
    Duration: 00:00:09.44, start: 0.540000, bitrate: 2743 kb/s
      Stream #0:0[0x1e0]: Video: mpeg1video, yuv420p(tv), 800x600 [SAR 1:1 DAR 4:3], 104857 kb/s, 25 fps, 25 tbr, 90k tbn, 25 tbc
      Stream #0:1[0x1c0]: Audio: mp2, 0 channels, s16p
     7.26 M-V:  0.000 fd=   0 aq=    0KB vq=   33KB sq=    0B f=0/0   
  </code></pre>
  
  <p>and no audible sound is played. The position of <code>-ac 2</code> doesn't change the behaviour, nor does repeating it only once. This is despite ffmpeg claims to record the audio with 2 channels, here is the input:</p>
  
  <pre><code>ffmpeg version N-71312-ga66dcfe Copyright (c) 2000-2015 the FFmpeg developers
    built with gcc 4.8.3 (GCC) 20140911 (Red Hat 4.8.3-7)
    configuration: 
    libavutil      54. 22.100 / 54. 22.100
    libavcodec     56. 34.100 / 56. 34.100
    libavformat    56. 29.100 / 56. 29.100
    libavdevice    56.  4.100 / 56.  4.100
    libavfilter     5. 13.101 /  5. 13.101
    libswscale      3.  1.101 /  3.  1.101
    libswresample   1.  1.100 /  1.  1.100
  Trailing options were found on the commandline.
  Input #0, x11grab, from ':0.0+0,0':
    Duration: N/A, start: 1428348285.201679, bitrate: N/A
      Stream #0:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 800x600, 25 fps, 25 tbr, 1000k tbn, 25 tbc
  Guessed Channel Layout for  Input Stream #1.0 : stereo
  Input #1, alsa, from 'pulse':
    Duration: N/A, start: 1428348285.225901, bitrate: 1536 kb/s
      Stream #1:0: Audio: pcm_s16le, 48000 Hz, 2 channels, s16, 1536 kb/s
   File 'output.mpeg' already exists. Overwrite ? [y/N] y
  [mpeg @ 0x2d079a0] VBV buffer size not set, using default size of 130KB
  If you want the mpeg file to be compliant to some specification
  Like DVD, VCD or others, make sure you set the correct buffer size
  Output #0, mpeg, to 'output.mpeg':
    Metadata:
      encoder         : Lavf56.29.100
      Stream #0:0: Video: mpeg1video, yuv420p, 800x600, q=2-31, 200     kb/s, 25 fps, 90k tbn, 25 tbc
      Metadata:
        encoder         : Lavc56.34.100 mpeg1video
      Stream #0:1: Audio: pcm_s16le, 48000 Hz, stereo, 1536 kb/s
  Stream mapping:
    Stream #0:0 -&gt; #0:0 (rawvideo (native) -&gt; mpeg1video (native))
    Stream #1:0 -&gt; #0:1 (copy)
  </code></pre>
  
  <p>I'm clueless. If anybody can tell me how to get this to work by either:</p>
  
  <ul>
  <li>fixing my mistakes in the command line flags</li>
  <li>if it's a regression, which revision to build from.</li>
  <li>any other way</li>
  </ul>
  
  <p>I'll buy him/her a pint.</p>