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
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
- frame rate =
- 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
- frame rate =
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