Timeshifting

The logic of timeshifting

A few things have already been explained in the section above, this will give an even more detailled explanation of what happens when you watch tv with MediaPortal. The logic of timeshifting is quite complicated, only read this if you have problems related to timeshifting or are really interrested in the details of how timeshifting works in MediaPortal.

When you watch tv the tv server tunes into a channel and starts receiving the tv signal. This signal is then written to a temporary file, called timeshift buffer (*.ts) by a component called tswriter. If a client want's to watch this tv signal it reads from this timeshift buffer with a component called tsreader. If the client is on the same computer as the server the file is accessed directly, if the client is on another computer the streaming component streamingserver reads the local timeshift buffer and then sends the video over the network using the rtsp protocol.

If the channel is scrambled, the tswriter sends the PIDs to the CAM so they can be decrypted. The time this is allowed to take is controlled with the setting Wait for unscrambled signal. If the tv server was able to decrypt the tv stream, the tswriter starts writing the tv stream into the timeshift files. At the same time the client's tsreader tries to start reading these file so it can output the tv signal to the screen. If the tsreader fails for longer than Wait for timeshifting file seconds to read from this file it will result in an error.

If all goes well and the client starts outputting the tv signal the tsreader always stays at the end of the the timeshift buffer (this position is called live point). At the same time the tswriter continues to write the tv stream into the timeshift buffer, which actually consists of 1 or more files (call tsbuffer files). Each file is Filesize MBytes large and can contain a certain time of tv signal depending on the content of the tv stream (SD/HD, subtitles, sound, etc.). After the file has reached the maximum size a new file is created and the tv stream is saved into this file. This is repeated until the Minimum amount of files have been created at which point the oldest file is being reused. This means that you can only go as far back in the tv stream as there is place in Minimum x Filesize MByte of storage. You can see an estimation of these values in the Timeshifting Info area of this section.

Now if you pause the live tv (maybe take a break, go for a walk, feed the dog,...) the tsreader stays at the current position while the tswriter still writes the tv stream to the timeshift buffer. This allows you to later on resume tv from the previous point and either watch time-displaced at normal speed or speed forward/jump forward to the live point. During the paused state the tswriter will continue to create new tsbuffer files until the Maximum number of files has been reached, at which point the tswriter will stop to write the tv stream to the hard disk. This means that all tv signal between this time (Maximum number of tsbuffer files has been reached) and the time when you resume watching tv, the tv stream is lost. When you later actually reach this point you will be forwarded to the time at which the tswriter started writing to the tsbuffer again (Livepoint when you resumed watching).