[mpeg2] question about the mpex and vbv buffer and vbv delay

[Luca Abeni <labeni@mbigroup.it>]

Hi all,

I am having some problems when trying to use an MPEX board to generate
digital tv programs to be played by a DVB receiver.

I am using an ASI output board to send to a DVB modulator the TS
generated by the MPEX, and then I am using a DVB receiver to test the
generated stream. Everything seems to work, but I can see sporadic
artifacts, and the video sometime freezes... Is anyone using the mpex in
a similar way? Is this a known problem? Any suggestions about how to fix
it?

Since someone pointed out that the problem could be related to buffer
overruns and underruns in the receiver, I am trying to have a look at
the buffering, and at the vbv in particular.
I am wondering if there is any way to set the vbv buffer size... I did
not find anything in the saa6752hs documentation, but maybe I missed
something... Any ideas?

Also, it seems that the MPEG2 video generated by the board always has
vbv_delay=0xFFFF... I checked a lot of DVB programs coming from the
satellite, and they all contain mpeg video with vbv_delay != 0xFFFF,
hence maybe this can be the problem... Does anyone know if the vbv_delay
generated by the mpex (always 0xFFFF) is correct, or if it is due to
some driver's setting that can be changed?

Finally, I am (obviously) encoding CBR video, but a TS analyzer that I
am using shows that the video bit rate is not that constant (it is
almost constant, but there are periodic spikes). Maybe this can be the
cause of the problem that I am seeing? If yes, does anyone know how to
obtain a "more constant" bitrate (maybe some of the encoding parameters
are not set in an optimal way for CBR encoding)?

			Thanks,
				Luca
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