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Sep 1, 2009 12:00 PM
Thoughts from Broadcast Engineering’s readers regarding articles on VHF allocations, splicing MPEG and long-GOP editing
VHF allocations
Dear Harry Martin:
I'm writing to ask a question about a statement in your August 2009 FCC Update column, “Cross-country moves.” You stated in the background paragraph that the FCC never allocated commercial VHF channels to New Jersey or Delaware. Did I miss something growing up in Delaware?
WDEL-TV started on Channel 7 in 1949 and later moved to Channel 12 in 1951. Its studios were (and buildings still are) on Shipley Road. It was a DuMont affiliate. I seem to remember that it was owned by Steinman Broadcasting, and later by Storer Broadcasting. I think the station went dark in the late 1950's, soon after the network shut down. At some point, the Channel 12 assignment was changed to non-commercial and co-licensed to Wilmington-Philadelphia, at which time the non-commercial broadcaster in Philadelphia (on Channel 35) asked the FCC for permission to move down to Channel 12. I think it was in 1963 that permission was granted by the FCC.
I'm sorry to be hazy on some of the details, but a quick Web search should confirm most of my memories.
I look forward to seeing more from you in Broadcast Engineering!
Cliff Schultz
Senior editor
Center City Film & Video
Philadelphia, PA
Harry Martin responds:
Section 331(a) of the Communications Act was passed in 1982. It provides that the FCC will, upon notification by an interested station, reallocate a VHF commercial TV station to a state that has none at the time of the request without regard other provisions of law. As of 2009, when the notifications were filed to allocate Channel 2 from Jackson, WY, to Wilmington, DE, there were no commercial VHF allocations to Wilmington.
The Channel 7 allotment to Wilmington in the 1940's is news to me. I am a bit of a neophyte, having been born only in 1945.
Splicing MPEG
Dear John Luff:
I was reading your “Splicing MPEG” article online at http://broadcastengineering.com/infrastructure/broadcasting_splicing_mpeg/, and I had a question. Say we have an MPEG-2 transport stream that is transmitted over wire — say MPGA. Is it possible to have another MPEG-2 transport stream (MPGB) to be spliced along with MPGA without having to uncompress the same? I want something like MPGA.1 MPGB.1 MPGA.2 MPGB.2 MPGA.3 to be transmitted, considering that MPGA has three splice points and MPGB has two splice points.
Jacob Jose Neroth
National Game Village
Bangalore
John Luff responds:
What you describe is precisely the intent of MPEG splicers. If the output stream can be variable bit rate, the bit rate of the two input streams does not matter. If, on the other hand, the inputs are different but the output must be constant bit rate, a transrating operation may be necessary in the process of splicing the two disparate streams into one.
Such a problem is often likely when a spot is dropped into a pre-existing stream, where the “hole” is a fixed and deterministic number of bits, and the spot must fit precisely. In part, this can be done by eliminating or adding nul packets (packets with no useful data that simply stuff the stream to match the intended bit rate) to make the splice a bit simpler to achieve. Lining up the GOP structure is the other critical part of the operation. And, of course, the integrity of the tables must be maintained.
Long-GOP editing
Dear Steve Mullen:
I read your “Long-GOP editing” article in the July 2009 issue and had a question. You mentioned that it is a good idea to edit natively in the long-GOP format and only convert on playback or output, etc. You also mentioned that you can send your material to Apple's color program in GOP format but that it will send it back to Final Cut Pro in ProRes. At that point, how do you integrate your color-corrected shots back into your sequence, seeing as they will now be in the ProRes codec as opposed to the long-GOP format you have been natively editing in?
Gabe Haggard
Post production coordinator
Santa Monica, CA
Steve Mullen responds:
Great question! Final Cut Pro 6, or higher, can mix long-GOP MPEG-2 and ProRes 422 in the same timeline. Not only does this feature allow you to “round-trip” to/from color, but also it enables you to render a complex MPEG-2 segment so it will play smoothly at full speed.
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