Difference between revisions of "Channel Scanning"

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The possible choices in this popup box does depend on the success of the scan
 
The possible choices in this popup box does depend on the success of the scan
 
and if the channels found are already in the database.
 
and if the channels found are already in the database.
If there are no channel yet for this video source then select '''Insert All'''.
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If there are no channels yet for this video source then select '''Insert All'''.
  
 
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Revision as of 09:02, 22 December 2019

How to do Channel Scanning

After doing the basic MythTV installation with network setup, storage directories and so on there comes the moment to find out which channels can be received. For DVB and ATSC the MythTV application mythtv-setup can do Channel Scanning, a process by which all channels that can be received are identified and stored in the database. Mythtv-setup is a separate application that can only run when mythbackend is not running because it needs the same tuner devices that mythbackend uses to make recordings. This guide describes how to do channel scanning with mythtv-setup.

But before we do that first a bit of explanation about the terminology.

What is a Video source 

The TV signal usually comes via a coaxial cable. This cable can come from a provider such as a DVB-C cable signal, or it can be linked to a DVB-T/T2 antenna or to a satellite dish for DVB-S/S2. In MythTV, the Video source does represent such an input signal. The result of the channel scan, a list of channels, is attached to the video source.

What is a Capture card 

To receive TV a tuner device is needed. This can be for example a PCIe card, an USB device or a networked tuner such as a HDHomeRun box. In MythTV a tuner is called a capture card. There can be two or more tuners on one card; these are then separate capture cards in MythTV.

What is an Input connection 

An input connection connects a capture card to a video source. The video source has the channel list so only via this connection the capture card has the information to tune to a channnel. Remember that this is just a software abstraction that enables a single list of channels to be shared among multiple tuners.

How the GUI works 

The mythtv-setup start page consists of a number of lines with items to be selected. The currently selected one is highlighted. With the up/down arrow keys another line can be selected.
A selection can be activated by pressing the space bar. This means that something actually happens. For instance, if the entry 2. Capture card is highlighted then after pressing the space bar the Capture cards page is shown. If there is a right arrow ">" shown at the end of the line then pressing the right arrow key brings you to the next menu level; pressing the left arrow key brings you to the previous menu level.

Configure a DVB-T/T2 tuner

Starting in the mythtv-setup main menu page, this are the steps to take. The steps described are for a DVB-T/T2 tuner but there are not many differences with other tuner types.

2. Capture card

Select the first choice: (New capture card)
This gives a new entry at the bottom of the list: New capture card
Note that this entry is without the brackets.

Select the New capture card and press the right arrow key.
There is now a single line Card type with a popup list of possible card types. The default value, and the one that is used in this example, is the DVB-T/S/C, ATSC or ISDB-T tuner card.

DVB device

The first line with label DVB device has a pop-up list of possible devices. A DVB device typically shows up as /dev/dvb/adapter0/frontend0. If you have only one tuner card then life is easy otherwise you do have to know which tuner you have to choose. To help with this the second line shows the Frontend ID.

Frontend ID

Information read from the tuner card. This can help with identifying the correct tuner card if there are more than one.

Delivery system

The type of DVB, such as DVB-T2 or DVB-C, is called a delivery system. There are capture cards that can receive multiple delivery systems. The popup menu shows the delivery systems that your capture card supports. If you want to receive a DVB-T or a DVB-T2 signal then select DVB-T2. If you want to receive a DVB-S or a DVB-S2 signal then select DVB-S2.

Signal timeout (ms)

Leave this at the default value. If there are problems with channels not being found this value can be increased to 7000ms.

Tuning timeout (ms)

Leave this at the default value. If there are problems with channels not being found this value can be increased to 10000ms. For non-encrypted channels this is always long enoug. Some TV cards with a Conditional Access Module (CAM) and a smartcard may need more time, up to 20 seconds.

Wait for SEQ start header

Leave at default (option is checked).

Open DVB card on demand

Leave at default (option is checked).

Use DVB card for active EIT scan

If you will use Schedules Direct or another source of guide data then uncheck this option. If you want to use the EIT to get the guide data then leave this option checked. If you have more than one capture card connected to the same video source then you need to select the active EIT scan only for one card.

DiSEqC (Switch, LNB and Rotor Configuration)

This option only appears if you have selected a DVB-S/S2 tuner device. More on this later as the current example is for DVB-T2.

Now that the capture card is configured, press the ESC (escape) key. In the popup menu select Save then Exit. Only if you do the Save then Exit the information is actually written to the database.


Recording Profiles

Skip this.

Video sources

Select the first choice: (New video source)
This gives a new entry at the bottom of the list: New video source

Note that this entry is without the brackets.

Select New video source and press the right arrow key.
This shows now the New video source page with a number of items to fill in.

Video source name

Anything can be used as the video source name but there must be something. The name of the provider, e.g. "Ziggo" or "Freeview" is a good choice.

Listings grabber

Default is Transmitted guide only (EIT). Other options are available when they have been configured elsewhere.

Channel frequency table

Leave at the default value (which is default).

Scan Frequency

This is the frequency that is used as the default value for a Full Scan (Tuned) channel scan. This is needed for a DVB-S/S2 and DVB-C scan because there you start tuning on a pre-defined frequency; from the signal on that frequency all the information about the other frequencies is obtained. For DVB-C this frequency is specified by the provider. For satellite the frequencies can be found on lyngsat.com or on linuxtv.org <example needed>. For DVB-T/T2 usually a Full Scan is done which scans all frequencies so then this field can be left empty.

Network ID

This is used only with DVB-C. Your provider has given you not only an initial frequency but also the network ID to use.

Bouquet ID

Select the bouquet ID for Freesat or BSkyB on satellite Astra-2 28.2E. Leave this at 0 if this video source is not used to receive this satellite. This is needed to get the Freesat or BSkyB channel numbers. More about this on page DVB UK.

Region ID

Select the region ID for Freesat or BSkyB on satellite Astra-2 28.2E. Leave this at 0 if this video source is not used to receive this satellite. This is needed to get the Freesat or BSkyB channel numbers. More about this on page DVB UK.

Now that the video source is configured, press the ESC (escape) key. In the popup menu select Save then Exit. Only if you do the Save then Exit the information is actually written to the database.

Input connections

This page shows a list of all capture cards and to which video source each capture card is connected. If there is no video source selected yet then (None) is shown. Select the capture card and press the right arrow key.

Delivery system

This shows the delivery system (modulation), for instance DVB-T2, that you have selected when you configured the capture card. This must be the same as the modulation used by the video source.

Display name

It is for some themes important that the last two characters of the name are unique. The default name is something like Input 11 and this name is guaranteed to be unique. If you have a lot of different capture cards then names like T0, T1 for the DVB-T2 tuners and C0, C1 for the DVB-C tuners are both short, descriptive and unique.

Video source

Default is (None) and that is not good. Press the space bar and select a video source.

Use quick tuning

Leave at default (Never).

Use DishNet long-term EIT data

Leave at default (not checked) unless you receive the DishNet satellites.

Scan for channels

If you press the space bar here you enter the Channel Scan dialog. This is what we want but first the other fields in the page are described.

Fetch channels from listings source

This is an alternative way of getting your channel configuration. Skip this if you want to do a channel scan.

Starting channel

This is the channel that is tuned to when Live TV is selected in mythfrontend. The popup list lets you choose one of the existing channels so this can be done only after the channel scan is completed. This value is not very important.

Interactions between inputs

Skip this for now. Wonderful features can be configured here but they are not needed for a channel scan.

This completes the configuration of the capture card. There are more choices to be made for a channel scan but these choices are not part of the capture card. The configuration of the capture card is stored in the database when you select Save then Exit as soon as this dialog box appears.

Now, after pressing the "Scan for channels", the page "Channel Scan" appears.

Channel Scan

The Channel Scan page does show an interesting list of options which we will describe one by one. Note that all these options are used only for this scan. The choices made are NOT saved in the database and for the next scan the options have to be set again.

Channel Scan

Desired Services

A typical signal can have not only TV channels but also radio channels and data channels. The default value is "TV" and then all channels that are not TV are discarded.

Unencrypted Only

This option is by default checked; it means that all encrypted channels are discarded and only the free-to-air channels which do not need to be decrypted are kept. Uncheck this option only if you do have the decoding hardware, such as a DVB card with a Common Interface and an activated smartcard.

Logical Channel Numbers required

The logical channel number information is sent by the broadcaster to set the channel numbers to nice values, e.g. BBC1 on channel number 1. This is something that TV's also do. If there are logical channel numbers in the signal then MythTV will always use them. This option is by default unchecked. If this option is checked, all channels that do not have a logical channel number are discarded. This is useful to filter out services for set-top-box firmware download and video-on-demand that can be present on a DVB-C signal.

Complete scan data required

This option discards all channels that do not have all required data. An example is a DVB channel that does not appear in the SDT (service description table) or that does not appear in both the PAT (program allocation table) and the PMT (program map table). On satellites there are many incomplete channels that are used for feeds or that are offline. This option is by default checked.

Full search for old channels

This option is checked by default. If this option is set, each scanned channel is compared with all channels in the database to see if the scanned channel is an update of an existing channel or if it is a new channel. If this option is not set, each scanned channel is only compared with the channels in the same multiplex.

Add full Transport Stream channels

The full transport stream contains everything that is received from the tuner. The full transport stream is also called the multiplex because it contains a number of TV and/or radio channels multiplexed together in one stream of bits. Creating a synthetic channel for this, e.g. MPTS_2300 or so, makes it possible to record it with mythtv. A full transport stream recording is typically used as input to a stream analyzer such as "DVB Inspector" which can tell you what every bit and byte in the stream means. This information can be used by developers to debug and enhance mythtv channel scanning and recording. This option is unchecked by default.

Test Decryptability

Test all scanned channels to see if they can be decrypted with the installed Conditional Access Module (CAM) and smartcard. This can be useful because sometimes the flag in the signal that indicates an encrypted signal is not correct. However, this check takes a very long time. This option is unchecked by default and it is recommended to leave it unchecked.

Video Source

This field shows the video source that is attached to the capture card. It is possible to change the video source here to any other video source that has a capture card connected to it.

Input

This field shows the currently selected capture card. If there are multiple capture cards connected to the same video source then it is possible to select any one of these capture cards.

Scan Type

The selected delivery system does determine which options are possible here. For DVB-T2 the "Full Scan" is the default choice. Now,pressing the right arrow key shows a country. This is a popup list; select the correct country. This determines the list of frequencies that is going to be tried. After making the selection press the left arrow key to go back to the Channel Scan page.

Scan

Pressing the space bar does actually start the scan!!!

SCANNING

This page shows the scanning progress. The Scan Progress bar goes from 0 to 100%. At the right/top corner you see ":Found: 17" which is the number of channels found so far. This is the "raw" number including all unwanted channels that are later filtered out, such as incomplete channels or data channels, depending on the options given.

When the scanning is ready there comes a popup box that says something like Found 33 new DVB channels. The possible choices in this popup box does depend on the success of the scan and if the channels found are already in the database. If there are no channels yet for this video source then select Insert All.

<TBD: channel scan page>
<TBD: rescan>
<TBD: Scan Type options> <TBD: cable> <TBD: satellite>
<TBD: satellite with diseqc switch>
<TBD: transport editor>
<TBD: video sources revisited>