Signaling frame rate information

[cconcolato]

AV1 elementary streams can carry frame rate information. The spec currently recommends not setting it:

The presentation times of AV1 samples are given by the ISOBMFF structures. The timing_info_present_flag in the Sequence Header OBU (in the configOBUs field or in the associated samples) SHOULD be set to 0. If set to 1, the timing_info structure of the Sequence Header OBU, the frame_presentation_time and buffer_removal_time fields of the Frame Header OBUs, if present, SHALL be ignored for the purpose of timed processing of the ISOBMFF file.

It might be worth clarifying how to signal fixed frame rate when used:

• in non-fragmented mode, by having a single entry in the stts box
• in fragmented mode, by setting the default_sample_duration in the trex. Note that this does not prevent fragments from overriding the value.

[cconcolato]

Note that MPEG is working towards recommending this approach.

[cconcolato]

We leave to the MPEG spec to describe how to signal frame rate.