[mythtv] Commercial Flagging Idea

[James Armstrong]

Mac Michaels wrote:
> On Wednesday 06 July 2005 08:29 am, James Armstrong wrote:
> 
>>Does the current commercial detection (Logo method)
>>detect not only the channel logo, but the TV Rating logo?
>>I have noticed that most of the shows in the US show the
>>TV rating immediately after the commercials when the show
>>resumes playing. It stays on the screen for about 5 to 10
>>seconds then goes away. It won't help with detecting the
>>beginning of the commercial but it would be a great way
>>to know when the commercials end.
>>
>>- James
> 
> 
> You may be on to something here. I don't know how the v-chip 
> works. Some research may be of value along this line as it 
> detects the TV Rating somehow. Is data sent during the 
> blanking interval that is used by the v-chip or does it 
> examine the video stream? Since advertisers always want 
> their stuff to be shown is there some special code that is 
> detected by the v-chip at the start of commercials? In the 
> US the FCC mandates the v-chip and requires all providers, 
> OTA and Cable, to transmit whatever the v-chip uses to 
> detect the rating for all shows.
> 
> I have seen some movie trailers shown as commercials that 
> contain a rating for the trailer.
> 

Going back to the show / commercial detection via v-chip. If / when vbi 
is working in mythtv:

v-chip data is in a XDS Extended Data Service packet in VBI Line 21 
field 2 and consists of 2 bytes. The packets are always in Field 2. The 
start code for an XDS packet is 0x07 and ends in 0x0F. The next byte 
after the start of the XDS is the packet type. I think v-chip data is 
0x01 0x05 for the first two bytes then the ratings. It is explained some 
at http://captioning.robson.org/articles/general/nv-line21.html

Another thought:

I am recording more and more HDTV shows. I wonder if an option would be 
to detect the audio type. I know there is a flag in the DTV data that 
tells if it is 5.1 and such. I wonder if the show is in 5.1 or something 
better than stander 2 channel audio, that the commercials would cut back 
to stereo. Basically when the audio switches between 5.1 or dolby and 
then to 2 channel stereo, that would indicate a commercial.

- James