[linux-dvb] Recording using a TwinHan VisionDVT terrestial card

[Tomas <psycho@pobox.com>]

Hello,

(If these are FAQs I'd appreciate links. The search engine at
	http://www.linuxtv.org/cgi-bin/htwrap.pl
doesn't give any results at all when searching for "record", so I
suspect there's some error there, and googling doesn't give any
real useful hits either. I've looked through linuxtv.org,
linuxdvb.tv and a few other sites without finding what I want.)

I want to to record using my TwinHan VisionDVT terrestial card.
Using
	mplayer -dumpfile file.ts -dumpstream dvb://CHANNEL
as described on
	http://www.mplayerhq.hu/DOCS/HTML-single/en/MPlayer.html
works, but I'm wondering if there's a better way of doing this
that people on this list prefer.

I've been using nvrec with transcode for several months to record
analog stuff, and am looking for similar solutions for digital
recording. What I want are simple command-line tools that can
easily be put in scripts run through crontab. DVR and ProjectX
looks like overkill for what I want (although ProjectX's A/V sync
stuff sounds good). The recording is to be done on a headless
machine without TV-out, and the files are then transferred to
another machine for viewing.

When using mplayer on a fast Athlon XP machine the CPU
utilization stays below 1% according to top, and the file size is
somewhere aroung 2GB/hour, which is fine, as I want to put the
card into an older and much slower machine which also has other
tasks such as acting as an ssh and www server, and thus don't
want to waste CPU cycles on anything but that which is needed to
dump the stream to disk (well, I guess A/V sync is worth spending
some CPU time on). Any processing (with the possible exception of
A/V sync) is done on the transport stream file when the recording
finishes, not while recording.

Also, is there some way of recording two channels simultaneously
using only one card? Is such a thing dependent on the card or the
drivers? I just get error messages from mplayer when I start up a
second recording, or try to view a second channel while
recording:
	DVB CONFIGURATION IS EMPTY, exit
	Failed to open dvb://CHANNEL2
The TwinHan web page for the card, located at
	http://www.twinhan.com/visiontv-2_2.htm ,
mentions "Viewing and Recording Different DTV Channels
Simultaneously" which to me sounds like it should be possible to
record two channels simultaneously, as it seems the card should
be able to deliver (at least) two channel streams simultaneously.

From what I can understand of the Metzler brothers' "The Linux
DVB API" paper, recording simultaneoulsy from two different
channels should be possible if the separation of transport
streams is done in software and not hardware, and one manages to
grab data from the frontend instead of the demux. Am I wrong
about this?

Using Linux kernel 2.6.6 with the included DVB drivers:
# lsmod
Module                  Size  Used by
dst                    14732  1
dvb_bt8xx               8068  0
dvb_core               87080  2 dst,dvb_bt8xx
crc32                   4352  1 dvb_core
bt878                  11568  2 dst,dvb_bt8xx
tuner                  18444  0
bttv                  152364  3 dvb_bt8xx,bt878
video_buf              21060  1 bttv
i2c_algo_bit            9736  1 bttv
btcx_risc               4808  1 bttv
i2c_core               23492  4 dvb_bt8xx,tuner,bttv,i2c_algo_bit
nvidia               2071432  22
rtc                    12664  0
# ls -l /dev/dvb/adapter0
total 0
crw-rw----    1 root     video    250,   1 Jun  8 16:15 audio0
crw-rw----    1 root     video    250,   6 Jun  8 16:15 ca0
crw-rw----    1 root     video    250,   4 Jun  8 16:15 demux0
crw-rw----    1 root     video    250,   5 Jun  8 16:15 dvr0
crw-rw----    1 root     video    250,   3 Jun  8 16:15 frontend0
crw-rw----    1 root     video    250,   7 Jun  8 16:15 net0
crw-rw----    1 root     video    250,   8 Jun  8 16:15 osd0
crw-rw----    1 root     video    250,   0 Jun  8 16:15 video0
#

Finally (yes!), a question about image quality: when I view live,
or play back a recording, there seems to be some interlacing
problem or similar. Fast vertical movements reveal horizontal
lines, most obvious when a TV program is using a blue screen
background for adding graphics, such as a weather report, but
disturbing also when watching regular programs.

/Tomas