[mythtvnz] Commercial Flagging

[David Moore]

On 18/08/11 16:25, Hadley Rich wrote:
> On Thu, 2011-08-18 at 16:18 +1200, Duncan Kennington wrote:
>> The important setting change I think for us was to set the maximum
>> commercial skip duration to 300 seconds (5 minutes) which catches all
>> the regular 4 minute breaks but doesn't allow it to miss the end of a
>> break and skip to the beginning of the next one.
>
I changed my setting from 3600(!? default?) to 300 and it helped 
slightly but still not real good results. I've tried a few things 
(methods: logo, blank, blankscene, all) on a few channels and get 50% or 
less detection of ads.

I have noticed that almost all ads on almost all channels do have fully 
or nearly black/blank frames before and after. I have run mencoder on a 
couple of recordings so far with the blackframes filter and it does a 
very good job at finding these black frames. But it's really slow and of 
course I need additional code to select appropriate blanks (not too hard 
I think) and push data into the recordedmarkup table (again not hard).

So questions:

1) Is anyone having better results with blank frame method for 
mythcommflag? I'm using myth 0.23-fixes (24158) and I wonder if the 
mythcommflag blank detection code has improved?

2) It seems to me that detecting blank frames should be very fast. Blank 
or near-blank frames should compress to almost nothing so you should be 
able to scan a video stream for frames with small sizes (in bytes) and 
only decode those instead of decoding the whole stream as mencoder (and 
mythcommflag?) seems to do. Of course I'm glossing over the whole IPB 
frame thing but I still think it should be possible to make a super-fast 
blank frame scanner. Anyone seen anything like this?

BTW I played around with audio analysis for a few recordings but it 
doesn't look like there is an easy way to use amplitude stats to 
reliably find ads. There are a truck-load of Linux audio tools out there 
so it's possible there is something which might work but too hard to find.

David