libextractor

GNU libextractor
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README.media (2307B)

      1 Provenance of the media samples
      2 ===============================
      3 
      4 Unlike the rest of the files in this directory, the three files below
      5 were not found anywhere: they are generated, and the recipe that
      6 generates them is `contrib/gen_testmedia.sh' in this repository.  Every
      7 frame and every sample comes out of FFmpeg's synthetic `lavfi' sources
      8 (a solid colour, a box, a sine wave), so there is no third party work
      9 involved and nothing to attribute.  They are dedicated to the public
     10 domain (CC0 1.0).
     11 
     12 They exist because the video thumbnail plugins (thumbnailffmpeg,
     13 thumbnailgst) and the audio preview plugins (previewopus, previewgst)
     14 need input that is long enough to seek around in, and none of the other
     15 test files here is even 30 seconds long.  Keeping them synthetic also
     16 keeps them small: all three together are smaller than a single one of
     17 the photographs in this directory.
     18 
     19 Theora and Vorbis in an Ogg container were chosen because both plugin
     20 backends can decode them without any additional codec package: FFmpeg has
     21 both built in, and for GStreamer they live in gst-plugins-base.
     22 
     23   subtitles.mkv           40s, Theora, 160x90, 5fps, subtitles eng/ger
     24                           (SubRip) and fre (ASS), flat black/white
     25                           stretches for the gallery (10K)
     26   thumbnail_pattern.ogv   90s, Theora, 160x120, 5fps, no audio (14K)
     27 
     28       Solid black for the first 20 seconds, then solid red.  The
     29       thumbnailers sample about 30 seconds in (bounded by a third of the
     30       duration, which is why the file is 90 and not 35 seconds long), so
     31       a thumbnail taken from the wrong moment comes out black instead of
     32       red, and test_thumbnailffmpeg/test_thumbnailgst notice.  Each frame
     33       also carries a small white box: the thumbnailers deliberately skip
     34       perfectly flat frames, which a fade-in leader would produce, and
     35       the box keeps the test from tripping over that.
     36 
     37   preview_tone.ogg        30s, Vorbis, mono, 8kHz (21K)
     38 
     39       A 440Hz tone for 15 seconds followed by an 880Hz tone.  8kHz mono
     40       is more than enough for something that gets re-encoded at 24 kbps.
     41 
     42   preview_tone.ogv        30s, Theora + Vorbis (28K)
     43 
     44       The same audio in a file that also carries video, so that the
     45       preview plugins are exercised on a video container as well.