title: FFMPEG: how to select audio stream without language metadata
body: <p>I have some source Video files with one or more audio streams inside.<br />
  I would to encode each source file with Italian language. Then I can do it.</p>
  <pre><code>ffmpeg -i source-file.avi -c:v ... -c:a ... -map 0:a:m:language:ita ...
  </code></pre>
  <p>But some source file has audio stream without Language metadata.<br />
  I look that it is possible to set Language metadata with &quot;und&quot; special value. Then I try to select the audio stream with this command:</p>
  <pre><code>ffmpeg -i source-file.avi -c:v ... -c:a ... -map 0:a:m:language:ita? -map 0:a:m:language:und? ...
  </code></pre>
  <p>(the &quot;?&quot; char say to ffmpeg that he do not fire exception if the audio stream do not exists).<br />
  Unfortunatelly this command do not works... It seems that ffmpeg search the &quot;und&quot; language instead of search a audio stream &quot;without&quot; language.</p>
  <h1>Video MetaData</h1>
  <p>This is the video MetaData where audio stream do not have language value:</p>
  <pre><code>Input #0, matroska,webm, from 'D:\My-Video.mkv':
    Metadata:
      title           : My-Video
      encoder         : libebml v1.3.3 + libmatroska v1.4.4
      creation_time   : 2016-01-20T16:02:03.000000Z
    Duration: 01:15:28.93, start: 0.000000, bitrate: 2775 kb/s
      Stream #0:0: Video: h264 (High), yuv420p(progressive), 720x576 [SAR 64:45 DAR 16:9], 25 fps, 25 tbr, 1k tbn, 50 tbc (default)
      Metadata:
        BPS             : 2387529
        BPS-eng         : 2387529
        DURATION        : 01:15:28.920000000
        DURATION-eng    : 01:15:28.920000000
        NUMBER_OF_FRAMES: 113223
        NUMBER_OF_FRAMES-eng: 113223
        NUMBER_OF_BYTES : 1351616420
        NUMBER_OF_BYTES-eng: 1351616420
        _STATISTICS_WRITING_APP: mkvmerge v8.7.0 ('All of the above') 64bit
        _STATISTICS_WRITING_APP-eng: mkvmerge v8.7.0 ('All of the above') 64bit
        _STATISTICS_WRITING_DATE_UTC: 2016-01-20 16:02:03
        _STATISTICS_WRITING_DATE_UTC-eng: 2016-01-20 16:02:03
        _STATISTICS_TAGS: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
        _STATISTICS_TAGS-eng: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
      Stream #0:1: Audio: ac3, 48000 Hz, 5.1(side), fltp, 384 kb/s (default)
      Metadata:
        BPS             : 384000
        BPS-eng         : 384000
        DURATION        : 01:15:28.928000000
        DURATION-eng    : 01:15:28.928000000
        NUMBER_OF_FRAMES: 141529
        NUMBER_OF_FRAMES-eng: 141529
        NUMBER_OF_BYTES : 217388544
        NUMBER_OF_BYTES-eng: 217388544
        _STATISTICS_WRITING_APP: mkvmerge v8.7.0 ('All of the above') 64bit
        _STATISTICS_WRITING_APP-eng: mkvmerge v8.7.0 ('All of the above') 64bit
        _STATISTICS_WRITING_DATE_UTC: 2016-01-20 16:02:03
        _STATISTICS_WRITING_DATE_UTC-eng: 2016-01-20 16:02:03
        _STATISTICS_TAGS: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
        _STATISTICS_TAGS-eng: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
      Stream #0:2(ita): Subtitle: dvd_subtitle, 720x576 (default)
      Metadata:
        BPS             : 2218
        BPS-eng         : 2218
        DURATION        : 01:09:57.232000000
        DURATION-eng    : 01:09:57.232000000
        NUMBER_OF_FRAMES: 965
        NUMBER_OF_FRAMES-eng: 965
        NUMBER_OF_BYTES : 1163769
        NUMBER_OF_BYTES-eng: 1163769
        _STATISTICS_WRITING_APP: mkvmerge v8.7.0 ('All of the above') 64bit
        _STATISTICS_WRITING_APP-eng: mkvmerge v8.7.0 ('All of the above') 64bit
        _STATISTICS_WRITING_DATE_UTC: 2016-01-20 16:02:03
        _STATISTICS_WRITING_DATE_UTC-eng: 2016-01-20 16:02:03
        _STATISTICS_TAGS: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
        _STATISTICS_TAGS-eng: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
  </code></pre>
  <p>Can someone help me?<br />
  Thanks!</p>