[Mp4-tech] output of deblocking filter

[Gary Sullivan]

I believe the answer to this question is not quite so simple.  See
remarks below.
Best Regards,
Gary Sullivan 
+> -----Original Message-----
+> From: mp4-tech-bounces lists.mpegif.org 
+> [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Robin Zoo
+> Sent: Wednesday, May 24, 2024 2:16 AM
+> To: mp4-tech lists.mpegif.org
+> Subject: [Mp4-tech] output of deblocking filter
+> 
+> Dear experts:
+> 
+> I noticed the following descriptions in MPEG2
+> standard:
+> 
+> "The output of the decoding process, for interlaced
+> sequences, consists of a series of reconstructed
+> fields that are separated in time by a field period"
+> 
+> "In progressive sequences each picture in the sequence
+> shall be a frame picture. The sequence, at the output
+> of the decoding process, consists of a series of
+> reconstructed frames that are separated in time by a
+> frame period"
I believe neither of those statements are actually necessarily true in
the MPEG2 low delay mode of operation.  They may be true outside of
low-delay operation.
+> 
+> I think the statements are true in H.264 decoding
+> process though I didn't found similar description.
This is not the case.  My advice is to not try to take statements out of
one standard and apply them to another.  Even if you could find some
case where an out-of-context quote may apply, the underlying definitions
of terms may differ.
In the case of H.264/MPEG-4 AVC, the output of the decoding process is a
series of pictures.
Pictures can be frames or fields.
There is no definition of an "interlaced sequence" or a "progressive
sequence" in H.264/AVC.
When fixed_frame_rate_flag is equal to 1, there are some strict
constraints on the relative timing of the output of pictures in
H.264/AVC.  When it is not, there aren't.
Also, I believe there is more of a notion of multiple sequences within a
single bitstream in the case of AVC than there is in MPEG-2.
+> 
+> Here is my question, for H.264 interlaced sequences,
+> if PAFF and MBAFF are in use, the output of deblocking
+> filter are mixed frame and field pictures which even
+> include frames containing mixed field or frame
+> macroblock pairs. Interlacing of frame or macroblock
+> pairs has to be done before sending the decoded pixel
+> for display. Is it true?
It is difficult to understand this question.  
Anyhow, display is outside of the scope of the standard.
+> 
+> thanks a lot!
+> 
+> Robinstain
+> 
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