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imf_track_files.md

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imf_track_files.md

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IMF Track Files

The MXF OP1a writer has an Interoperable Master Format (IMF) flavour that helps with the creation of IMF Track Files (as defined in SMPTE ST 2067-2). The flavour makes it easier to create IMF Track Files by pre-selecting certain required options. However, it does not have knowledge of all the Track Files defined for IMF (across SMPTE ST 2067-2, the IMF Applications, the IMF Plug-ins, etc) and it does not enforce compliance. For example, it does not check that the input essence and metadata will result in a compliant Track File.

The IMF flavour is enabled using the -t imf clip type option in bmxtranswrap and raw2bmx. This results in the following settings for OP1a,

  • fill after the header metadata is at least 8192 bytes (--head-fill 8192)
  • index table follows the essence, even for clip-wrapped audio (--index-follows)
  • creates partitions every 60 seconds for frame-wrapped essence (--part 60)
  • audio clip-wrapping (--clip-wrap)
  • combines audio into a single track by default (--track-map singlemca)
  • adds a Primary Package property (--primary-package)
  • disables creation of timecode tracks (--no-tc-track)
  • adds the audio Channel Assignment label descriptor property and sets it to the IMF label by default (--audio-layout imf). Use the --audio-layout option to override this default value.
  • add the Display F2 Offset and sets it to 0 for progressive JPEG 2000 and RDD 36 video (--display-f2-offset 0)

The settings can be found in the code by searching for the OP1a define OP1A_IMF_FLAVOUR and the descriptor define MXFDESC_IMF_FLAVOUR. E.g. see if ((flavour & OP1A_IMF_FLAVOUR)) in src/mxf_op1a/OP1AFile.cpp for the bulk of the settings.

IMF Track Files contain only a single essence component. bmx provides support for creating such files. If the input MXF files contain multiple essence tracks then use options such as --disable-video, --disable-audio, --disable-data and --track-map to disable tracks.

A number of topics related to creating complete IMF Track Files can be found in the docs/ directory, including Multi-channel Audio Labels, Timed Text, JPEG 2000 and ProRes.

The bmxtranswrap and raw2bmx tools allow setting metadata defined in SMPTE ST 2067-2,

  • Reference Image Edit Rate (--ref-image-edit-rate)
  • Reference Audio Alignment Level (--ref-audio-align-level)
  • Active Height (--active-height)
  • Active Width (--active-width)
  • Active X Offset (--active-x-offset)
  • Active Y Offset (--active-y-offset)
  • Alternative Center Cuts (--center-cut-4-3 and --center-cut-14-9)

and SMPTE ST 2067-21 - Application #2E,

  • Mastering Display Primaries (--display-primaries)
  • Mastering Display White Point Chromaticity (--display-white-point)
  • Mastering Display Maximum Luminance (--display-max-luma)
  • Mastering Display Minimum Luminance (--display-min-luma)

IMF Track File names conventionally include the UUID material number of the top-level file source package UMID. This can be accomplished automatically by supplying an output filename argument as a pattern, such as -o {Type}_{fp_uuid}.mxf. This example pattern results in a filename beginning with VIDEO, AUDIO or DATA, such as VIDEO_a145db5d-4623-4233-913f-15e16980b840.mxf, but can be tuned with the --ess-type-names parameter.