[M4IF Technotes] interlaced content in MPEG-4

[Richard Shields]

Gaurav,
If I recall correctly, there are two bits in each macroblock that indicates
whether or not Field DCT or Field prediction was used to encode the
macroblock.  So, when the VOL header indicates interlace compression what it
really is indicating is that there are extra elements in the bitstream that
govern how each macroblock is to be decompressed.  You can indicate
interlace compression for the sequence but never use Field DCT or Field
prediction.  Of course you are then using two extra bits for each macroblock
except for four motion blocks which only supports field DCT and thus uses
one extra bit.
-Richard
> -----Original Message-----
> From: Gaurav Aggarwal [mailto:guraaf   yahoo.co.in]
> Sent: Sunday, January 26, 2024 9:57 PM
> To: Technotes
> Subject: [M4IF Technotes] interlaced content in MPEG-4
> 
> Hi all,
> 
> Is it true that in MPEG-4 either all VOP will be progressive or all
> interlaced? MPEG-2 had two syntactic entities: progressive_sequence
> and progressive_frame. There it is possible to have a sequence where
> prog_seq=0 but still get pictures with prog_frame=1.
> 
> In MPEG-4, there appears to be a single entity called "interlaced"
> at video_object_layer. Now, this VOL is similar to a sequence, and
> there is no interlaced/prog flag at the VOP layer. Is it correct to
> say that either all pictures are progressive or all are interlaced?
> 
> Also, doesn't MPEG-4 support Pan Scan? It appears that there are no
> display sizes. Only source sizes coded as video_object_layer_width
> and video_objet_layer_height. Is it true that the stream doesn't
> have the panning capabilities that MPEG-2 video had?
> 
> Thanks,
> Gaurav
> 
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