DVB-C Scan Problems

[Fordli]

Dear all
since V35 on linux/ubuntu I have major problems when scanning DVB-C (using 2 different cards/philipps + 1 USB stick/suntek). With all of them I get:
a) about half of the transport streams are scanned ok and the corresponding channels are ok
b) about half of the transport streams generate timeout problems

The channels for a) are then mostly ok (for live watching and recoding), some of them however generate timeout as well as tinmouts when attempting to watch them.

I already tried
- set signal & tuning timouts to larger values (20'000ms)
- re-scan with different sligthly modified frequencies for transport
No effect so far.

In previous versions of mythtv, no problem with that, scanning worked as expected with the 3 tuners, tuning to the channels as well.

Any ideas what could help?
Thanks!

[dnalorernst]

The usual questions:

Which OS Version ? Post the output of

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uname -a

and

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lsb_release -a

Which version of MythtvTV you are running?

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mythbackend --version

Is the MythTV install consistent? Every version needs to be the same of

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dpkg -l | grep myth

Do the tuners need additional firmware? This page might help:
https://www.linuxtv.org/wiki/index.php/ ... nformation
Also looking at 'dmesg' could give some information.

Does 'dvbscan' or 'dvbv5-scan' or 'w_scan2' (see https://forum.mythtv.org/viewtopic.php?p=29188#p29188) work?

If not done already, update to the latest v35 version using the ppa:
https://launchpad.net/~mythbuntu/+archive/ubuntu/35
Note: You need to run 'apt-get dist-upgrade' after enabling the ppa to get everything in place

[Fordli]

Thanks for your reply!

All 3 tuner cards worked with previous versions (< 0.35)
Additional firmware for the cards is installed, and the command "w_scan_cpp -fc -cCH" works and does find the channels (especially also the ones with problems/timeouts in myht).

Details:

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uname -a
Linux mserver2 6.8.0-87-generic #88-Ubuntu SMP PREEMPT_DYNAMIC Sat Oct 11 09:28:41 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux

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lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 24.04.3 LTS
Release:	24.04
Codename:	noble

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mythbackend --version
Please attach all output as a file in bug reports.
MythTV Version : v35.0+fixes.202511050005.7e93f0d37b~ubuntu24.04.1
MythTV Branch : fixes/35
Network Protocol : 91
Library API : 35.20220913-1
QT Version : 5.15.13
Options compiled in:
 linux profile use_hidesyms using_alsa using_oss using_pulse using_pulseoutput using_backend using_bindings_perl using_bindings_python using_bindings_php using_dvb using_firewire using_frontend using_hdhomerun using_satip using_vbox using_ceton using_joystick_menu using_libcrypto using_gnutls using_libdns_sd using_libxml2 using_lirc using_mheg using_opengl using_egl using_qtscript using_qtdbus using_taglib using_v4l2 using_v4l2prime using_x11 using_system_libbluray using_system_libudfread using_systemd_notify using_systemd_journal using_drm using_bindings_perl using_bindings_python using_bindings_php using_freetype2 using_mythtranscode using_opengl using_egl using_drm using_vaapi using_nvdec using_vdpau using_ffmpeg_threads using_mheg using_libass using_libxml2 using_libmp3lame

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dpkg -l | grep myth
ii  libmyth                                       2:35.0+fixes.202511050005.7e93f0d37b~ubuntu24.04.1 amd64        Common library code for MythTV and add-on modules (runtime)
ii  libmyth-python                                2:35.0+fixes.202511050005.7e93f0d37b~ubuntu24.04.1 all          Python library to access some MythTV features
ii  libmythtv-perl                                2:35.0+fixes.202511050005.7e93f0d37b~ubuntu24.04.1 all          Perl library to access some MythTV features
ii  mytharchive                                   2:35.0+fixes.202511050005.7e93f0d37b~ubuntu24.04.1 amd64        create and burn DVD's from MythTV - binary file
rc  mythbuntu-bare-client                         2.7.2                                              all          Mythbuntu Bare Client
rc  mythbuntu-common                              0.78.2                                             all          Mythbuntu application support functions
rc  mythbuntu-control-centre                      0.64.1                                             all          Mythbuntu Configuration Application
ii  mythbuntu-default-settings                    1.13                                               all          default settings for Mythbuntu
ii  mythbuntu-lightdm-theme                       1.01                                               all          Mythbuntu LightDM setup
ii  mythexport                                    2.2.4-0ubuntu7                                     amd64        Export MythTV recording to portable media players
ii  mythmusic                                     2:35.0+fixes.202511050005.7e93f0d37b~ubuntu24.04.1 amd64        Music add-on module for MythTV
ii  mythtv                                        2:35.0+fixes.202511050005.7e93f0d37b~ubuntu24.04.1 all          Personal video recorder application (client and server)
ii  mythtv-backend                                2:35.0+fixes.202511050005.7e93f0d37b~ubuntu24.04.1 amd64        Personal video recorder application (server)
ii  mythtv-backend-master                         2:35.0+fixes.202511050005.7e93f0d37b~ubuntu24.04.1 all          Metapackage to setup and configure a "Master Backend" profile of MythTV
ii  mythtv-common                                 2:35.0+fixes.202511050005.7e93f0d37b~ubuntu24.04.1 amd64        Personal video recorder application (common data)
ii  mythtv-database                               2:35.0+fixes.202511050005.7e93f0d37b~ubuntu24.04.1 all          Personal video recorder application (database)
ii  mythtv-frontend                               2:35.0+fixes.202511050005.7e93f0d37b~ubuntu24.04.1 amd64        Personal video recorder application (client)
ii  mythtv-status                                 1.1.0-1                                            all          Show the status of a MythTV backend
ii  mythtv-theme-mythbuntu                        2:35.0+fixes.202511050005.7e93f0d37b~ubuntu24.04.1 all          MythTV Theme used in the Mythbuntu distribution
ii  mythtv-transcode-utils                        2:35.0+fixes.202511050005.7e93f0d37b~ubuntu24.04.1 amd64        Utilities used for transcoding MythTV tasks
rc  mythweb                                       2:34.0+fixes.20240210.e3e165a1-0ubuntu6            all          Web interface add-on module for MythTV
ii  php-mythtv                                    2:35.0+fixes.202511050005.7e93f0d37b~ubuntu24.04.1 all          PHP Bindings for MythTV

[white_haired_uncle]

All 3 tuner cards worked with previous versions (< 0.35)

On the same OS, or did you upgrade (or reinstall) that at the same time?

[Fordli]

Mythtv was upgraded AFTER ubuntu, so yes, scanning worked with Mythtv (<v35) and the actual LTS.

Besides:

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w_scan_cpp -fc -c CH -L > channels.xspf
 

works still as expected, generating a file including all channels (also the ones not found by Mythtv). When using VLC with this file, all the channels can then be displayed without errors.

The scanning in Mythtv finds sometimes some few additional channels (but never all of them), but when selecting those then in the live TV, I always get an error (Tuning timeout), but an increased timeout does not help (up to 25sec).

[Fordli]

When scanning with MythTV (using different dvb-c cards), I get typically output like below:

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Transport ID 657 - Zeitüberschreitung, Keine Sender
Transport ID 634 - 19 mögliche Sender gefunden
Transport ID 623 - 7 mögliche Sender gefunden
Transport ID 622 - Zeitüberschreitung, 5 mögliche Sender
Transport ID 621 - 4 mögliche Sender gefunden
Transport ID 615 - 13 mögliche Sender gefunden
Transport ID 614 - 18 mögliche Sender gefunden
Transport ID 612 - 7 mögliche Sender gefunden
Transport ID 605 - Zeitüberschreitung, 60 mögliche Sender
Transport ID 602 - 6 mögliche Sender gefunden
Transport ID 601 - 23 mögliche Sender gefunden
Transport ID 604 - 52 mögliche Sender gefunden
...

The problem here are the lines like "Zeitüberschreitung, xy mögliche Sender"=Timeout, xy possible channels" (timeout is configured as 20sec!).

But when using VLC, there is no timeout, and the corresponding channels can be viewed without problems!

[dnalorernst]

Please post on the MythTV v35 installation the backend log of a channelscan.
Start mythbackend as usual.
Set the verbose level:

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sudo -u mythtv mythbackend --setverbose general:notice,chanscan:debug

Do the channel scan and paste the link to the logfile.

It would be a great help to do the same on the MythTV v34 installation,
but you should backup the database beforehand, see

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https://wiki.mythtv.org/wiki/Database_Backup_and_Restore

and restore it afterwards.

[Fordli]

Ok, clear install MythTV V34 on new Ubuntu 24.04.3 LTS. Scan gives no timeouts.
Scan log file: logV34.log

Update to MythTV35
Scan log file: logV35.log

Both logs available at:
https://drive.switch.ch/index.php/s/O2d9wpbj055iLCx

So, again, lots of timeouts in V35. Increasing signal + tuning timouts does not help (20'000ms), and also "ignore Signal Timout" has no effect.
Any ideas?
Both scans using "scan of all existing transports" and "search new transports".

[Fordli]

For finding the problems in the V35 log file -> look for the string "Timed out" !

[Fordli]

No answers so far... Am I really the only one with this problem?
Any idea?

[kmdewaal]

I am having a look at your log files. This might actually be a bug but I cannot reproduce it on my system.

[kmdewaal]

Please do a scan on V35 with the option "Logical Channel Numbers Required" selected and report the result.

I do think that there is something going wrong in the postprocessing stage of the channel scanning.
This is done differently in V35 compared to V34.
It looks like "good" channels are discarded and "bad" channels are kept, and then the "bad" channels are discarded because the tuning data is incomplete. This all very much depends on the channel data that is received during scanning but that can be very different on different signal sources.
To be continued.

[Fordli]

Thanks for your input!
The scan with V35 + "Logical Channel Numbers Required" does not change the situation. I've put the new log (file "logV35_withLogicalChannelNum.log") to the same location as mentioned above.

(My DVB-C provider moved some channels to other tranports etc., hence I get now timeout errors partly on other channels/transports; so the new log may not be easily comparable with the old ones. However, the main problem persists as before...)