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  1. Member godai's Avatar
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    im recording a channel for long time ago but sometime its changing i just curious about whats happening.

    its a 720p [or 720i?] air atsc channel first i get a 6.6 gb file per hour , since 3 weeks ago size go to 5.4 gb and just two days ago its 4.6 gb.

    what can be reason for that? thank you
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  2. Seems like they changed bitrate. I don't know what kind of stream it is broadcasted, like H.264/AVC with Dolby digital (AC-3). Here where I live we have these codecs and some others too and it is stored in ts streams which has a huge overhead.
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    Has the broadcaster added any new secondary channels? There is only so much bandwidth available to divide between the primary channel (usually HD) and the secondary channels (usually SD) sharing the same frequency.
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  4. Dinosaur Supervisor KarMa's Avatar
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    They can shift bitrate from one channel to another channel on the same frequency, like 10.1 and 10.2. Or they could've switched from a constant bitrate to a more variable bitrate, which would better allocate bitrate between channels on the same frequency.

    Nearly (if not completely) all of US ATSC broadcasts are MPEG2 AC3, just to clear that up.
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  5. Perhaps more efficient encoding (as such reduced bitrate as others suggested) - seem there is lot of work in US to improve overall MPEG-2 efficiency.
    http://www.ateme.com/technology-leadership/knowledge-center/white-papers/using-avch-26...cept-a-reality
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  6. Dinosaur Supervisor KarMa's Avatar
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    Originally Posted by pandy View Post
    Perhaps more efficient encoding (as such reduced bitrate as others suggested) - seem there is lot of work in US to improve overall MPEG-2 efficiency.
    http://www.ateme.com/technology-leadership/knowledge-center/white-papers/using-avch-26...cept-a-reality
    They require you to fill out some info and your email. So I'll just post the pdf here.
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  7. Member godai's Avatar
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    Originally Posted by usually_quiet View Post
    Has the broadcaster added any new secondary channels? There is only so much bandwidth available to divide between the primary channel (usually HD) and the secondary channels (usually SD) sharing the same frequency.
    channel comes with another one but it was always in that way before and now. its a 480i channel.



    other tv company have a hd channel in different frequencies but in one its a subchannel [1 hour its 3.6 gb] and other its main channel [4.6 gb per hour] only difference its first one come without cc
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  8. Different videos require different bitrates. There's no reason a TV station has to broadcast the same bitrate all the time.
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  9. Member godai's Avatar
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    Originally Posted by jagabo View Post
    Different videos require different bitrates. There's no reason a TV station has to broadcast the same bitrate all the time.

    you probably right. but i capture a lot. and usually general size of files never changed.
    for example in this case , file was 6.6 gb for 4 years.
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  10. Dinosaur Supervisor KarMa's Avatar
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    They could also be planning on adding a new channel or maybe the new channel is already there. My local NBC station had only one channel which was 1080i, and it always stayed at 15Mbit video bitrate. Now there are two SD channels along with the original 1080i. The 1080i now uses around 10.5Mbit, and has more pronounced macroblocks with the drop in bitrate. Same with my FOX station which broadcasts in 720p, they started out at 15Mbit and then dropped to like 9Mbit after adding two SD channels.
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  11. Originally Posted by KarMa View Post
    Originally Posted by pandy View Post
    Perhaps more efficient encoding (as such reduced bitrate as others suggested) - seem there is lot of work in US to improve overall MPEG-2 efficiency.
    http://www.ateme.com/technology-leadership/knowledge-center/white-papers/using-avch-26...cept-a-reality
    They require you to fill out some info and your email. So I'll just post the pdf here.
    My fault, sorry, side to your upload there is also direct link available:
    http://ateme.com/IMG/pdf/using_avc_h.264_and_h.265_expertise_to_boost_mpeg-2_efficiency.pdf
    and some other interesting papers:
    https://static.aminer.org/pdf/PDF/000/322/504/adaptive_gop_structure_selection_for_rea...o_encoding.pdf
    https://tech.ebu.ch/docs/techreview/trev_304-mpeg2.pdf

    I think there some initiative currently ongoing in ATSC area ("ATSC+" or something like this AFAIR) to improve various aspects of the total network capacity.

    There is also interesting paper showing how MPEG-2 efficiency improved across 2 decades - to deliver same quality bitrate was reduced more than twice and knowing fact that usually metrics are PSNR based some psycho-visual tuning may still refine MPEG-2.
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  12. Dinosaur Supervisor KarMa's Avatar
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    Broadcasters still have a set bandwidth to fill, so they aren't going to just let bandwidth go unused if it can be helped. Even if they use improved MPEG-2 codecs, they would still use it all.
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