VLC and DVB-C command line parameters

[Nicu]

Hey there!

I want to use VLC to stream from my DVB-C tuner, so I can use whatever mobile device I want in my house to watch TV. Kaffeine works just fine with the tuner, but I hope to get it to run with VLC too. I got no video output from "Open Capture Device", and streaming failed the same:

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Your input can't be opened: VLC is unable to open the MRL 'dvb-c://frequency=370000000:modulation=QAM:srate=6900000'. Check the log for details.

VLC log:

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main debug: processing request item: dvb-c://frequency=386000000, node: Playlist, skip: 0 main debug: rebuilding array of current - root Playlist main debug: rebuild done - 1 items, index 0 main debug: starting playback of new item main debug: resyncing on dvb-c://frequency=386000000 main debug: dvb-c://frequency=386000000 is at 0 main debug: creating new input thread main debug: Creating an input for 'dvb-c://frequency=386000000' main debug: requesting art for new input thread qt debug: IM: Setting an input main debug: using timeshift granularity of 50 MiB main debug: using default timeshift path main debug: `dvb-c://frequency=386000000:modulation=64QAM:srate=6900000' gives access `dvb-c' demux `any' path `frequency=386000000:modulation=64QAM:srate=6900000' main debug: creating demux: access='dvb-c' demux='any' location='frequency=386000000:modulation=64QAM:srate=6900000' file='(null)' main debug: looking for access_demux module matching "dvb-c": 17 candidates main debug: no access_demux modules matched main debug: creating access: dvb-c://frequency=386000000:modulation=64QAM:srate=6900000 main debug: looking for access module matching "dvb-c": 27 candidates dtv error: cannot access adapter 1: No such file or directory dvb warning: unknown option (modulation=64QAM:srate=6900000) main debug: no access modules matched main debug: dead input

I can't explain the error, nor the warning, because I used the VLC GUI to specify the modulation and symbol rate values - taken from Kaffeine.

Here's my tuner's dmesg data:

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[ 962.644162] usb 1-1: new high-speed USB device number 4 using ehci-pci [ 962.811184] usb 1-1: New USB device found, idVendor=15f4, idProduct=0131, bcdDevice= 1.00 [ 962.811188] usb 1-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0 [ 962.811191] usb 1-1: Product: dvbt2 [ 962.811194] usb 1-1: Manufacturer: astrometadvbt2 [ 962.852466] mc: Linux media interface: v0.10 [ 962.865844] usb 1-1: dvb_usb_v2: found a 'Astrometa DVB-T2' in warm state [ 963.012956] usb 1-1: dvb_usb_v2: will pass the complete MPEG2 transport stream to the software demuxer [ 963.012966] dvbdev: DVB: registering new adapter (Astrometa DVB-T2) [ 963.012970] usb 1-1: media controller created [ 963.013297] dvbdev: dvb_create_media_entity: media entity 'dvb-demux' registered. [ 963.022026] i2c i2c-8: Added multiplexed i2c bus 9 [ 963.022031] rtl2832 8-0010: Realtek RTL2832 successfully attached [ 963.029065] i2c i2c-8: cxd2841er_attach(): I2C adapter 00000000a340bd96 SLVX addr 6e SLVT addr 6c [ 963.033393] i2c i2c-8: cxd2841er_attach(): attaching CXD2837ER DVB-C/T/T2 frontend [ 963.033398] i2c i2c-8: cxd2841er_attach(): chip ID 0xb1 OK. [ 963.033405] usb 1-1: DVB: registering adapter 0 frontend 0 (Realtek RTL2832 (DVB-T))... [ 963.033415] dvbdev: dvb_create_media_entity: media entity 'Realtek RTL2832 (DVB-T)' registered. [ 963.033629] usb 1-1: DVB: registering adapter 0 frontend 1 (Sony CXD2837ER DVB-T/T2/C demodulator)... [ 963.033636] dvbdev: dvb_create_media_entity: media entity 'Sony CXD2837ER DVB-T/T2/C demodulator' registered. [ 963.037790] r820t 9-003a: creating new instance [ 963.045087] r820t 9-003a: Rafael Micro r820t successfully identified [ 963.045092] r820t 9-003a: attaching existing instance [ 963.063805] r820t 9-003a: Rafael Micro r820t successfully identified [ 963.086650] videodev: Linux video capture interface: v2.00 [ 963.095312] rtl2832_sdr rtl2832_sdr.3.auto: Registered as swradio0 [ 963.095314] rtl2832_sdr rtl2832_sdr.3.auto: Realtek RTL2832 SDR attached [ 963.095316] rtl2832_sdr rtl2832_sdr.3.auto: SDR API is still slightly experimental and functionality changes may follow [ 963.102384] Registered IR keymap rc-empty [ 963.102442] rc rc0: Astrometa DVB-T2 as /devices/pci0000:00/0000:00:1a.7/usb1/1-1/rc/rc0 [ 963.102579] rc rc0: lirc_dev: driver dvb_usb_rtl28xxu registered at minor = 0, raw IR receiver, no transmitter [ 963.102634] input: Astrometa DVB-T2 as /devices/pci0000:00/0000:00:1a.7/usb1/1-1/rc/rc0/input14 [ 963.102801] usb 1-1: dvb_usb_v2: schedule remote query interval to 200 msecs [ 963.111515] usb 1-1: dvb_usb_v2: 'Astrometa DVB-T2' successfully initialized and connected [ 963.111626] usbcore: registered new interface driver dvb_usb_rtl28xxu

This happens on both Linux Mint 19.3 64-bit - VLC 3.0.8 - and the latest Raspbian on a Raspberry Pi 4 - VLC 3.0.16. Kaffeine works fine on both, VLC doesn't. But should it work, and how?

[Rémi Denis-Courmont]

You've configured VLC to use adapter number 1 which does not exist on the system.

[Nicu]

I tried adapter1 because adapter0 didn't work either - same result in the GUI log. But I see the debug log shows something different for adapter0, this time complaining about "invalid argument".

This one is on the Raspberry Pi (VLC 3.0.16):

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main debug: processing request item: dvb-c://frequency=370000000, node: Playlist, skip: 0 main debug: rebuilding array of current - root Playlist main debug: rebuild done - 1 items, index 0 main debug: starting playback of new item main debug: resyncing on dvb-c://frequency=370000000 main debug: dvb-c://frequency=370000000 is at 0 main debug: creating new input thread main debug: Creating an input for 'dvb-c://frequency=370000000' main debug: requesting art for new input thread main debug: using timeshift granularity of 50 MiB main debug: using default timeshift path main debug: `dvb-c://frequency=370000000:modulation=QAM:srate=6900000' gives access `dvb-c' demux `any' path `frequency=370000000:modulation=QAM:srate=6900000' main debug: creating demux: access='dvb-c' demux='any' location='frequency=370000000:modulation=QAM:srate=6900000' file='(null)' main debug: looking for access_demux module matching "dvb-c": 19 candidates main debug: no access_demux modules matched main debug: creating access: dvb-c://frequency=370000000:modulation=QAM:srate=6900000 main debug: looking for access module matching "dvb-c": 29 candidates main debug: looking for meta fetcher module matching "any": 1 candidates lua debug: Trying Lua scripts in /home/pi/.local/share/vlc/lua/meta/fetcher lua debug: Trying Lua scripts in /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/fetcher lua debug: Trying Lua scripts in /usr/share/vlc/lua/meta/fetcher main debug: no meta fetcher modules matched main debug: looking for art finder module matching "any": 2 candidates lua debug: Trying Lua scripts in /home/pi/.local/share/vlc/lua/meta/art lua debug: Trying Lua scripts in /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art lua debug: Trying Lua playlist script /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art/00_musicbrainz.luac dtv debug: conditional access module not available: No such file or directory dtv debug: setting property 2 to 0 dtv debug: setting property 17 to 1 dtv debug: setting property 3 to 370000000 dtv debug: setting property 4 to 6 dtv debug: setting property 8 to 6900000 dtv debug: setting property 9 to 9 lua debug: skipping script (unmatched scope) /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art/00_musicbrainz.luac lua debug: Trying Lua playlist script /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art/01_googleimage.luac lua debug: skipping script (unmatched scope) /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art/01_googleimage.luac lua debug: Trying Lua playlist script /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art/02_frenchtv.luac lua debug: skipping script (unmatched scope) /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art/02_frenchtv.luac lua debug: Trying Lua playlist script /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art/03_lastfm.luac lua debug: skipping script (unmatched scope) /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art/03_lastfm.luac lua debug: Trying Lua scripts in /usr/share/vlc/lua/meta/art main debug: no art finder modules matched qt debug: IM: Setting an input dtv error: cannot set frontend tuning parameters: Invalid argument dtv error: tuning to 370000000 Hz failed dvb warning: unknown option (modulation=QAM:srate=6900000) main debug: no access modules matched main debug: dead input qt debug: IM: Deleting the input main debug: changing item without a request (current 0/1) main debug: nothing to play

P.S. By the way, why does VLC list adapters that don't really exist? The spinner allows me to go up to adapter99.

[Rémi Denis-Courmont]

The parameters are either invalid or not supported by the tuner.

Indeed QAM is not a valid modulation.

[Nicu]

VLC uses "QAM" as a parameter when I leave it on "Automatic". This is obviously a problem for users unaware that that setting could cause problems, just as we can choose up to 99 adapters, most of which don't exist.

Now I specified the modulation and added all the advanced options VLC offered me. But "unknown option" seems to me like VLC does something wrong - either the GUI generates wrong options, either the error reporting is wrong. If the tuner doesn't support something, the least VLC can do is properly report what's wrong.

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main debug: processing request item: dvb-c://frequency=514000000, node: Playlist, skip: 0 main debug: rebuilding array of current - root Playlist main debug: rebuild done - 1 items, index 0 main debug: starting playback of new item main debug: resyncing on dvb-c://frequency=514000000 main debug: dvb-c://frequency=514000000 is at 0 main debug: creating new input thread main debug: Creating an input for 'dvb-c://frequency=514000000' main debug: requesting art for new input thread qt debug: IM: Setting an input main debug: looking for meta fetcher module matching "any": 1 candidates lua debug: Trying Lua scripts in /home/pi/.local/share/vlc/lua/meta/fetcher lua debug: Trying Lua scripts in /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/fetcher lua debug: Trying Lua scripts in /usr/share/vlc/lua/meta/fetcher main debug: no meta fetcher modules matched main debug: looking for art finder module matching "any": 2 candidates main debug: using timeshift granularity of 50 MiB main debug: using default timeshift path main debug: `dvb-c://frequency=514000000:modulation=256QAM:srate=6900000' gives access `dvb-c' demux `any' path `frequency=514000000:modulation=256QAM:srate=6900000' main debug: creating demux: access='dvb-c' demux='any' location='frequency=514000000:modulation=256QAM:srate=6900000' file='(null)' main debug: looking for access_demux module matching "dvb-c": 19 candidates main debug: no access_demux modules matched main debug: creating access: dvb-c://frequency=514000000:modulation=256QAM:srate=6900000 main debug: looking for access module matching "dvb-c": 29 candidates lua debug: Trying Lua scripts in /home/pi/.local/share/vlc/lua/meta/art lua debug: Trying Lua scripts in /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art lua debug: Trying Lua playlist script /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art/00_musicbrainz.luac lua debug: skipping script (unmatched scope) /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art/00_musicbrainz.luac lua debug: Trying Lua playlist script /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art/01_googleimage.luac lua debug: skipping script (unmatched scope) /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art/01_googleimage.luac lua debug: Trying Lua playlist script /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art/02_frenchtv.luac lua debug: skipping script (unmatched scope) /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art/02_frenchtv.luac lua debug: Trying Lua playlist script /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art/03_lastfm.luac lua debug: skipping script (unmatched scope) /usr/lib/arm-linux-gnueabihf/vlc/lua/meta/art/03_lastfm.luac lua debug: Trying Lua scripts in /usr/share/vlc/lua/meta/art main debug: no art finder modules matched dtv debug: conditional access module not available: No such file or directory dtv debug: setting property 2 to 0 dtv debug: setting property 17 to 1 dtv debug: setting property 3 to 514000000 dtv debug: setting property 4 to 5 dtv debug: setting property 8 to 6900000 dtv debug: setting property 9 to 0 dtv error: cannot set frontend tuning parameters: Invalid argument dtv error: tuning to 514000000 Hz failed dvb warning: unknown option (modulation=256QAM:srate=6900000) main debug: no access modules matched main debug: dead input

Here's what Kaffeine shows about the TV station I had just tried to watch in VLC:

[Rémi Denis-Courmont]

Same as before: the driver rejects at least one of the tuning parameters. The Linux DVB API is such that userspace can't tell which one, unfortunately.

[Nicu]

Based on the Kaffeine screenshot, what do you think I should pass as parameters for VLC to have a shot at playing anything back?

[Nicu]

Well... I tried looking into Kaffeine's source code, to see how they make it work, but my C/C++ skills are insufficient. They use libVLC, which makes me wonder what's the difference between what the library has to offer, compared to what the VLC gui allows the user to do with the hardware - by presumably using the same library. I also went to the KDE forums to ask for help with the Kaffeine source code, and so far (3 weeks) I got no reply. It was a long shot, though, considering Kaffeine doesn't have a dedicated forum.

Can you guys please take a look at what they do with libVLC and figure out how they made it work? And is there any other information that I can provide you for this purpose?

[Rémi Denis-Courmont]

LibVLC is not doing anything interesting or relevant for DVB. You need a string describing the tuning parameters just as you do with VLC.

[Rémi Denis-Courmont]

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dtv debug: setting property 2 to 0 dtv debug: setting property 17 to 1 dtv debug: setting property 3 to 514000000 dtv debug: setting property 4 to 5 dtv debug: setting property 8 to 6900000 dtv debug: setting property 9 to 0 dtv error: cannot set frontend tuning parameters: Invalid argument dtv error: tuning to 514000000 Hz failed

That means: clear settings, DVB-C, 514 MHz, 256-QAM, 6.9 Mbauds, no FEC in that order. The device driver rejects it.

[Nicu]

LibVLC is not doing anything interesting or relevant for DVB. You need a string describing the tuning parameters just as you do with VLC.

That makes me wonder if a debug build would output that string to the terminal. I don't know if they compile libVLC (probably not) along with Kaffeine, or they rely on it to be pre-installed. Maybe if force a custom Kaffeine build to use a debug build of libVLC I could catch all these strings. I just don't know which "knobs" to turn to get there.