Reply from linuxtv list about MythTV and DVB-T problems that have been observed with USB units. Any comments?
On 9/30/05, Patrick Boettcher <[EMAIL PROTECTED]> wrote: > Hi Adrian, > > I read the ticket, but I never used MythTV so far, anyway, I think you are > facing "normal" problems: > > 1) IMHO Myth should not rely on the signal-strength and > signal-to-noise-ratio. The different hardware which is in use in the > different devices are producing different results (because of calculation > problems (not floats in kernel-space) and differences). For DVB/ATSC > devices MythTV should rather monitor the LOCK-status, BER and UNC to form > an opinion about the signal-quality. (For the nova-t-usb2 there is > additionally a bug/mistake in pseudo-signal-calculation, which leads to a > signal-strength of zero when the signal is actually _very_ good.) > > 2) USB1.1 devices (and USB2 devices running on a USB1.1 hub) that are > using BULK transfers for MPEG2-TS transfer are facing a problem. The > bandwidth of USB1.1 is not enough for receiving the complete transport > stream of a DVB-T channel (which is about 12 to 16 MBit/s). That's why all > DVB devices on USB1.1 using a PID filter in hardware to just get the > packets with the requested PIDs. > > Problem: > If only a PAT is requested it will take a quite long time to fill the > BULK-transfer buffer. The BULK-URB won't return to the driver (and thus to > the demux/section-filter) unless it is full. (That's why Malc has to use > -5 as a parameter of dvbscan to get something (because the PID 0x10 (NIT: > network information) is only repeated with a larger interval and it is > small too)). > > Unfortunately I had problems by reducing the buffer-size of URBs (so that > it won't take too long to get the URBs back)... which would be a solution. > > This problem does not exist for USB1.1 device using isochronous transfers > for MPEG2-TS delivery. > > Patrick. > > -- > Mail: [EMAIL PROTECTED] > WWW: http://www.wi-bw.tfh-wildau.de/~pboettch/ > > > On Thu, 29 Sep 2005, Adrian Wilkins wrote: > > A number of us are having problems with MythTV and DVB-T, mostly with > > USB tuners, it seems. > > > > The longest thread on their bugtracker regarding this is > > http://svn.mythtv.org/trac/ticket/343 > > > > In particular, it's puzzling me that both my USB tuners, a Nova-T and > > a DEC2000t, will record fine at the command line (using tzap), but > > refuse to work with MythTV (they have previously worked just fine, it > > seems to be the new signal monitoring code that Myth has introduced). > > > > The output from tzap looks weird though, esp. the Nova-T, which > > reports zero signal as soon as it gets a proper lock (meh?). This is a > > card that will stream a playable (mplayer) TS to disk with no trouble, > > but Myth refuses to watch that channel. > > > > The problem would may be that Myth is waiting for PAT/PMT to appear > > and considers it to be absent. The developers speculate that this may > > be a driver problem. > > > > One assertation by a developer was that Myth probably gives the API a > > bigger workout than your applications and that he might be able to > > provide code that would break things ; I'm sure that would prove a > > tasty challenge. > > > > I'm happy to perform whatever contortions necessary to aid resolving > > this, as my wife is upset because House, MD hasn't recorded for four > > consecutive weeks now and she's getting withdrawal symptoms ;-) > _______________________________________________ mythtv-dev mailing list [email protected] http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-dev
