blank screen no audio/video - please read this

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blank screen no audio/video - please read this

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zappp64

Senior Member

24. January 2007 @ 13:26

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ok so one day you come home sit down to watch Sky Sports but all you get is a blank screen with no video or audio - however the FTA (free to air) channels like BBC1 and Channel 4 are ok

well lets start by explaining a bit about how the dbox descrambles the cable signal

The DBOX descrambles the cable signal - The actual fundamentals of the image do not decode the channels - the image is simply a standard linux operating system.

There are two types of stream sent out by the cable company:

FTA - These channels are broadcast 'in the clear' and are not scrambled in any way. Typically this is BBC1, BBC2, ITV1 and Cbeebies (maybe a few others). In other words they are the freeview channels; and anybody can stick a box on the end and obtain them.

Nagra Encrypted - These channels are broadcast as 'scrambled'. In other words, they need to be decoded before you will see a sound and picture. It needs to be decrypted first via use of a 'key' The cable system works similar to this.

The 'keys' are sent down the video/audio stream, but the box needs to know what to do with them, how to recognise them, and how to process them. This is where a softcam comes in. The encrypted channels are the subscription ones that they want you to pay for - for example the Movies and Sports channels.

In a standard/legitimate box, you have a digital smartcard which processes all the data and reacts to it. The smartcard is the one that looks for, receives, and processes these 'keys' which will decode the channel. But we don't use a card with the DBOX2 do we, so whats going on there then??

On top of the image is a 3rd party program which we refer to as a 'softcam' - it emulates a smartcard. You would have heard of it as evocamd, newcamd, mgcamd, or maybe even gbox. This programs work by simulating an inserted card and processing commands in the stream. They were written by studying the smartcards and their processors, and working out what commands do what function. By doing this, a softcam is essentially a digital clone of a smartcard in an unphysical form.

The 'softcam' grabs the keys from the stream and saves them into a file on the box [a real smartcard would store these in permanent memory]. Whenever you change channel, this file is then read, and the stream is decoded using these sets of keys or passwords.

The cable company send 'commands' down the stream called ECMs which tell boxes that the key has changed, and that the systems need to be updated. The softcam receives this command and compares the two sets of keys - if the newer keys are different then it saves those instead. This is known as 'autoroll' or 'autoupdate'. If the softcam didnt recognize and save the newer keys then the encrypted channels would not be able to be displayed, because the 'key' to unlock them would not be correct and the stream would still be encoded. Therefore you see a blank screen.

To view this ECM information, using FTP go to the tmp folder on the dBox
and look for a file called ecm.info - this is a standard text file with the 'key' to descramble the channel.

Therefore to update or autoroll the key - all you need to go to is go to a channel like Sky Sporst 1 - wait for a while (a minute at the most) and this ecm.info file will be updated with the new key.


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