[M4IF Technotes] packet_header macroblock number

Richard Shields richard sorenson.com
Thu Jan 30 10:10:11 EST 2003


Ariel,
If you are receiving your packets through a protocol such as RTP then packet
loss can occur.  So, yes, the situation you have run into can occur and the
decoder must know how to handle it.  There are various methods of error
concealment (handling the missing macroblocks) from just copying the
collocated macroblocks from the reference frame or by using some type of
interpolation from the surrounding macroblocks.  The handling of missing
macroblocks is not covered by the specification.
-Richard
-----Original Message-----
From: Ariel David [mailto:Ariel.David   ParthusCeva.com] 
Sent: Thursday, January 30, 2024 7:48 AM
To: technotes   lists.m4if.org
Subject: [M4IF Technotes] packet_header macroblock number
Hi,
I've run across a problem where I decode a stream and get to a resync
marker.
I decode the packet_header and in it decode the macroblock number of the
start of the next packet.
The problem is that this macroblock number is not identical to my own
macroblock count.
This means that in my decoder I am supposed to be for example in macroblock
75 and the macroblock number in the packet_header shows 80.
I now have 5 macroblocks that are unacounted for.
I've looked through the standard and see no mention of such an even and how
to resolve it.
The main problem is that I don't know if this is a bitstream error or
something that can possibly happen and I need to handle.
Is this occurance at all possible?  Is this an error?  Should I decode these
macroblocks as skipped?
P.S  I hope I reached the correct address.  I am subscribed to technotes,
but saw no address to send questions.
Thanks,
Ariel
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