[mythtv-users] Varying data formats during digital reception

Mike Perkins mikep at randomtraveller.org.uk
Sat Nov 3 14:35:31 UTC 2012

I've been prompted to ask this question since I've spotted a number of posts 
here that indicate a potential problem regarding digital reception. The basic 
problem is this:

(i) For analog reception, the tuner did the encoding and you set it to encode to 
whatever bitrate, etc you desired. Your file was a fixed format.

(ii) For digital reception, the tuner does exactly that, it tunes to the 
multiplex and either pulls a stream out or passes the whole mux forward, ie 
there is /no/ encoding. Whatever is received gets dumped to disk as is.

The problem is that the broadcaster may vary the bitrate, resolution, framerate 
etc of the transmission at any time. Within the contents of a Transport Stream 
(TS) this is perfectly valid: any TV just decodes what it gets from moment to 
moment and throws it onto the screen.

In practice this may mean that program content may have a different format to 
that of any advert break, program trailer, or the previous or next program.

Then I read this, in a post concerning the Lossless-Cut utility:

"I am not sure if you loaded these recordings yourself or there is some issue 
with the database but no matter what Lossless Cut needs to find the type "32" 
recordedmarkup record and a valid FPS number. Typically the recordedmarkup 
records are created by MythTV as soon as the recording starts. Lossless cut uses 
the chanid, starttime and type=32 as the keys to find the correct record."

This of course is useless, since the stream format at the beginning of the 
recording may bear no relationship *at all* to that of the bulk of the program 

The question is: What changes are being made to mythtv to cope with the fact 
that the bitrate, framerate, resolution, etc of any recorded file may change 
from instant to instant?


Mike Perkins

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