[M4IF Technotes] question about top_field_first!

[Gaurav Aggarwal]

Yes, your understanding is correct. Each field of a frame goes for half the
frame time, so if let us
say you are running a video at 30 frames per second (NTSC) then each field
goes out for 1/60th
of second.
Also, as you point out, it is essential that the two fields go out in
consecutive time slots. You can
introduce another field from a different frame between two fields of the
same frame. Further, make
sure you look at the repeat_first_field also in conjuction with the
top_field_first flag. If both are set
then the display is T B T, if top_field_first is 0 then the display will be
B T B.
If it helps to know, the behavior of these flags is the same as MPEG-2
video.
Hope this helps,
Gaurav
  -----Original Message-----
  From: technotes-admin   lists.m4if.org
[mailto:technotes-admin   lists.m4if.org]On Behalf Of Xue Xuhong
  Sent: Friday, January 10, 2024 8:04 AM
  To: M4if Technotes
  Subject: [M4IF Technotes] question about top_field_first!
  Dear Experts,
  We know ASP Profile includes Interlace Tool. In syntax, top_field_first is
a parameter about interlace, whose meaning is defined as below(reference to
w3056):
  “This is a 1-bit flag which when set to “1” indicates that the top field
(i.e., the field containing the top line) of reconstructed VOP is the first
field to be displayed (output by the decoding process).  When
top_field_first is set to “0” it indicates that the bottom field of the
reconstructed VOP is the first field to be displayed “
  As it describes, when reconstructed VOP is to be displayed,
top_field_first is an useful information to control which field should be
first displayed.
  We wonder that whether  it is necessary to display the two fields of the
reconstructed VOP in consecutive different time? That is, when
top_field_first =1, then the top field should be displayed first , and it
will hold for 1/2 Tframe(Tframe is the frame period ), then the bottom field
should be displayed, and it will hold the  remained  1/2 Tframe.
  Is our understanding right?
  Thanks for your help!
  Regards,
  Xue Xuhong
-------------- next part --------------
An HTML attachment was scrubbed...
URL: /pipermail/mp4-tech/attachments/20030110/4592ee91/attachment.html