Hi all,
after installing an additional dvb-t card in a system with two pvr 250
that worked absolutely wonderful for months with 0.2.0-rc3f i had to
upgrade the kernel from 2.4.31 to 2.6.12.6 to get the dvb-t working.
I tried to install 0.2.0-rc3k, but there were probs with the cx88xx
module, needed for the dvb-t, because of missing symbols in
tveeprom.ko.
Then i gave a try to 0.3.8, and installation was smooth and worked
fine, except one problem: Recordings using the pvr 250s show mpeg
artifacts, sound drop outs and sometimes even the video steps, i.e.
some tenths of a second simply are missing. This happens not very
often, about every ten or fifteen minutes i guess. Sometimes it
happens more frequently and sometimes it does not happen at all for an
hour or so.
It seems that other system activities, esp. hard disc access, would
increase the problem. Playing with buffer sizes did not help.
First i tried "modprobe ivtv yuv_buffers=4 mpg_buffers=8 vbi_buffers=4
pcm_buffers=4" to have all these buffers doubled compared to the
defaults, then i tried "modprobe ivtv yuv_buffers=1 mpg_buffers=2
vbi_buffers=1 pcm_buffers=1", which gives half the sizes, but there
was no alleviation.
Then i came back to 0.2.0-rc3k yesterday and bravely used tveeprom
from the kernel, not the version included in ivtv, so there are no
unresolved symbols anymore and surprisingly both pvr 250s and the
dvb-t card work fine now (and i am satisfied, no probs for me now).
But it is obvious that something in 0.3.8 has changed compared to the
0.2.0 versions that causes recording problems.
Some background information:
I tune with ptune.pl and I use ivtvctl to set bitrate, dnr_mode,
stream_type and such. I then "cat /dev/videoX > <file>". No other
software does interfere with ivtv, there is only the kernel, ivtv and
cron.
The box is an AMD Athlon 2200+ on a Gigabyte 7n400s-l mobo with
512mb ram. There are three ata hard disks connected. Hda is an old
IBM DTLA with 40gb, hdb is a quite new IBM 250gb and hdc is a Maxtor
250gb. The Maxtor is the recording disk and is only used for recording
and playback. The system is a combined dsl network firewall and digital
video recorder, and there are no other system activities.
When recording two 8mbit/s video streams with both pvr simultanously
the system load is 0.15 to 0.20, and with ivtv 0.2.0-rc3f and 2.4.31
installed i would see no video degradation even if i started to copy 10gb
from hdc to hdb while these two recordings were running.
The problem started when i installed 0.3.8 and it disappeared after i left
0.3.8 behind and installed 0.2.0-rc3k, so i do not think it has to do
anything with the dvb-t card. It is possible to do two 8mbit/s recordings
with the pvrs and a third 2.2mbit/s recording with the dvb-t at the same
time without any quality degradations.
Finally i should mention that i never used any 0.3.x version before,
because there were no problems with the 0.2.0 versions i have had.
A big "Thank you" to Chris Kennedy and all others involved in
development, this is great stuff :-)
Best regards
Leo
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