[mythtv] Random blockiness that probably isn't CPU or PCI bus bandwidth-related

Taylor Jacob rtjacob at earthlink.net
Wed Jan 19 00:46:59 EST 2005


Duplicated sequence numbers will not ever happen unless you drop 15 consecutive
packets.. FEC is supposed to take care of errors and sending extra packets of
the same payload defeats the purpose of this..

The DVB PS code I used to have huge issues with attempting to record HD content
from PBS (would produce unwatchable garbage), but the latest fixes from Marucs
Metzler (and possibly updated drivers) seem to have fixed this.. I only
recently tried again to record HD over satellite..  In TS mode I have not seen
a problem recording HD content.. Some of the full featured DVB cards the
filtering chip av7110 doesn't seem to be able to handle the bandwidth of HD
streams, there is some discussion on linux-dvb.. You can turn off hardware
filtering and do it in software and that supposedly fixes the problem..

I would investigate your signal levels and see if you have a high BER.. If the
demodulator cannot fix a packet with FEC alone it will drop it, and I am not
sure if this "uncorrectable bit" error gets displayed depending on what card
you are using.. This could also be the issue.. It is possible that a weaker FEC
scheme is being used and a few bad packets are slipping through.. FEC is never
pefect..

It also could be a driver issue..

I would start to look there..

I suspect its not in either the PS or TS code in myth.. TS is very simple and if
you are using the DVB-Patch 3.5 it uses many common routines in dtvrecorder.cpp
to flag the GOPs in the DB..

Sort of a ramble, but there are my thougths on this issue..

Taylor


More information about the mythtv-dev mailing list