title: what is COLOR_FormatYUV420Flexible?
body: <p>I wish to encode video/avc on my android encoder. The encoder (Samsung S5) publishes COLOR_FormatYUV420Flexible as one of its supported formats. yay!</p>
  <p>but I dont quite understand what it is and how I can use it. the docs say:</p>
  <blockquote>
  <p>Flexible 12 bits per pixel, subsampled YUV color format with 8-bit chroma and luma components.</p>
  <p>Chroma planes are subsampled by 2 both horizontally and vertically. Use this format with Image. This format corresponds to YUV_420_888, and can represent the COLOR_FormatYUV411Planar, COLOR_FormatYUV411PackedPlanar, COLOR_FormatYUV420Planar, COLOR_FormatYUV420PackedPlanar, COLOR_FormatYUV420SemiPlanar and COLOR_FormatYUV420PackedSemiPlanar formats</p>
  </blockquote>
  <p>This seems to suggest that I can use this const with just about any kind of YUV data: planer, semi-planer, packed etc. this seems unlikely: how would the encoder know how to interpret the data unless I specify exactly where the U/V values are?</p>
  <p>is there any meta-data that I need to provide in addition to this const? does it just work?</p>