Rename initial presentation delay fields.

[tomfinegan]

This editorial change renames the initial presentation delay fields to avoid confusion between the ISOBMFF value, which is in samples, and the AV1 bitstream value, which is in frames.

• Rename initial_presentation_delay_present to initial_display_delay_present.
• Rename initial_presentation_delay_minus_one to initial_display_delay_in_samples_minus_1.

Closes https://github.com/AOMediaCodec/av1-isobmff/issues/104

[tomfinegan]

rawgit is shutting down; this will work:

https://htmlpreview.github.io/?https://github.com/AOMediaCodec/av1-isobmff/blob/a126a8c9e88f69ca49a18f720cb25e215eaa6cac/index.html

[cconcolato]

I'm not sure removing 'presentation' removes the confusion. #104 actually suggested renaming it to initial_display_delay_in_samples_minus_1. If we have to rename, I think I would prefer that.

[rbouqueau]

I also think the new name is more confusing than the previous one. initial_display_delay_in_samples_minus_1 is better ; couldn't we re-use the show_frame e.g. initial_show_frame_delay_in_samples_minus_1 ?

[tomfinegan]

I also think the new name is more confusing than the previous one. initial_display_delay_in_samples_minus_1 is better ; couldn't we re-use the show_frame e.g. initial_show_frame_delay_in_samples_minus_1 ?

I think show_frame makes things more confusing than using display. I think this is more clear because the field carries the value of initial_display_delay_minus_1 in samples.

edit: add preview link, https://htmlpreview.github.io/?https://github.com/AOMediaCodec/av1-isobmff/blob/d62b085c6d190165d18059fc483e47b2573f9a32/index.html

[tomfinegan]

Dropping this as it doesn't really seem necessary.