[MPlayer-users] Re: Video Filter for Black Frame Detect

Brian J. Murrell brian at interlinx.bc.ca
Fri May 2 00:24:01 CEST 2003

On Thu, 01 May 2003 13:47:49 -0700, usene wrote:

> Very cool.  I knew I couldn't be the first to think of this.


I thought that the better way to do this was detect and mark black frame
groups during capture, as you have to process every frame anyway.  The
capture process could create an EDL file marking each black frame group
and then heuristics could be used to edit out the commercials, like
removing any segment between black frames <= 30 seconds, or even 60

Or you could just leave the stream intact and have keys which skip back
and forward between EDL markers.

> Couldn't you combine black frame detect along with a seek (+10, +5, +1) to get
> better performance?

Sure you could, but you decrease the accuracy in that you could seek past
the black frame(s) when you are jumping ahead.

> ie. seek 4 seconds, bf detect for 1 second, seek for 4
> seconds, .....

I suspect you will end up jumping over as many black frame groups as you
find doing this.  I don't think it will be very effective.

> Algorithmically, how could you detect you were back in the show as opposed
> to in another commercial?

Because the next black frame(s) is more than 30-60 seconds away.  This
process works better for editing commercials out of a stream than for
real-time skipping of commercials -- which is why I think marking them
during capture and then simply copying the stream to a new stream,
skipping short segments is the best process.

> I've also wondered if anyone has collected empirical knowledge regarding
> when commercials occur.  

I don't think it's accurately predictable.  It's generally predictable
though.  Ever notice when you channel surf on commercials in one program,
a lot of other programs are in commercials too (I'm in North America;
YMMV depending on where you live)?

> -Do commercials appear at the exact same time in every showing of a specific 
>  episode?  For example can I apply an EDL to every episode of South

No way.

> -Or is this by network?  
> -Are commercials always 30 seconds and 60 seconds?

I think commercials are always fixed amounts (15, 30 are common) but I
think commercial groups are not always exact multiples of some value.

The thing I have thought would be interesting is for network broadcasts,
if one person finds (i.e. manually inspects a stream) the "frame number"
where commericial blocks start and end, other people could use them to
edit out commercials from their own capture from the same network.  Like a
clearing house.


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