[mythtv-users] Commercial Flagging (UK, DVB-T)

[D. R. Newman]

On 26/10/12 09:22, Tim Phipps wrote:

> My contribution to MythTV is here:
>
> http://www.mythtv.org/wiki/Commercial_detection_with_silence_for_UK_freeviewHD
>
>
> It's based on the one above but works on DVB-T2 as well, does not need
> to transcode the audio stream and can be run in realtime.

I tried this, it often works well, but it is not doing the same as 
mythcommflag_wrapper, as it ignores the minimum time for silence.

Although min is passed as a parameter to mausc.c, it is never used. 
mausc.c looks for silence in a single video frame, 1/25th of a second, 
not all along 0.15 seconds (or whatever min has been set to). As soon as 
there is a silent video frame, gapstart is set, so it reacts to 0.04 
seconds of silence.

The result is that if there is a short silence in a programme, it is 
treated as an advert break, instead of being ignored.

It is easy to drop short breaks, like this:

     if (!silent && last_silent) {
       if (frames < gapstart + min)
         gapstart = 0
       else
         gapend = frames
     }

but that only works on the first break (e.g. the start of an advert). We 
also need code to check that the silence at the end of an ad break is > min.

Also, I wonder how we deal with recordings that start in the middle of 
an advertisement, so the first silence is the end of a break? For those 
of us who start recordings a few minutes before the scheduled time, that 
is often the case.

David Newman