Tomas wrote:
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 LinuxDVB 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?
dvbstream can be used to save N programs from a transponder, and it's a grab-only program (so as light as can be):
dvbstream -f 11766 -p V -s 27500 -o:r1.ts 512 650 -n 7200 -o:r2.ts 513 660 -n 3600 -o:mix.ts 512 660 -n 1800
(-n indicates the number of seconds to save for each program). You can also mix each pid in multiple dumps.
Nico
