IMF FAQ

by Mr. MXF

I get asked a lot of IMF questions and you can contact me if you have one. Many questions are not confidential and many of them are repeated over and over again, so here's a few of them to help you wander the IMF information forest in relative safety.

Q == question. A == short answer. R == references info. E == example

nav: | duration | filenames |

Durations

• Q#1885 - My tracks have identical durations - why does netflix still reject my files?
  • A: All tracks need identical durations - with no rounding and no floating point
  • R: [ST 2067-3] last sentence of section 7.2 says The duration of the Segment shall be equal to the duration of its Sequences and all Sequences within a Segment shall have the same duration. When you have fractional frame rates, there is not always an integer number of audio samples in the duration of a video frame. This means that the duration each IMF segment with a frame rate of 29.97fps or 59.94fps needs to be a multiple of 5 frames to get exact synchronisation.
  • E: ❌ Fail example
    • frame rate = 30000/1001 fps
    • clip duration = 51 frames
    • clip duration = 81681⅔ audio samples @48kHz
    • There is no integer number of audio samples to make the track durations identical. Pad the video track with a black frame at the beginning/end and add some silence to fix
  • E: ✓ Success example
    • frame rate = 30000/1001 fps
    • clip duration = 50 frames
    • clip duration = 80080 audio samples @48kHz
    • Clip duration is a multiple of 5 frames - just works

Filenames

• Q#1886 - What is the maximum filename length in IMF?
  • A: IMF does not use filenames so there is no upper limit
  • R: ST 2067-2 does not mention filenames. ST 2067-2 IMF Core Constraints references ST 429-9 Asset Map. In ST 429-9 clause 7.1 defines an Asset's Path as a URI defined by RFC 3986. A URI that has global scope should not exceed 255 characters. Filenames are definitely not global scope and are therefore unconstrained by any standard.
  • E: local scope: cpl-c7f5e0cd-52e1-42f2-8d5b-cd6607f678b4-DERIVED-FROM-a8dbb61c-d2ee-4b34-9188-5cbffcb6c0c6-DERIVED-FROM-15bd6a26-d8cf-4625-83de-451f91d9023b -DERIVED-FROM-4c293f11-13d2-4252-92a1-9dc729c46f68.xml is a valid filename but may break some QC tools.
  • E: global scope: https://s3.eu-west-2.amazonaws.com/mrmxf-public/www/samples/plan-text-sample.txt is 90 chars