OTA TV Bandwidth

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  • #51188
    mwdxer1
    Participant

    I was checking out the bandwidth the Portland stations use. Some are fixed and others vary. KATU 2.1 is listed at 3.4 mbps. Isn’t that a bit narrow for and HD transmission, even if only in 720p? Others like KOIN 6.1 is at 9.1 mbps and KPTV (Also 720p) at 6.7. Hard to tell with KGW 8.1 or KOPB 10.1 as they vary. 12.2 SD COZI is really narrow at .9 and Bounce 49.3 at .95. I am surprised you can get a decent picture with under 1 mbps.

    #51189
    DarkStar
    Participant

    It’s all variable bitrates these days, so it all varies quite a bit depending on content.

    The encoders are able to take all the incoming video streams and perform a statmux across all of them to determine what bits can be shared across them to make more efficient encodings.

    I’ve noticed that typically 1080i content will utilize more bits than 720p, so for the KATU example that is important since KRCW 32.1 is also encoded on their bitstream currently. Once you add the three diginets (MeTV, Comet, and TBD), you realize that 19.39 Mbps can only be chopped up in so many ways.

    #51190
    boisebill
    Participant

    Idaho PTV runs two 1080i and three more 480 SD channels.
    At the moment ‘Daniel Tiger’ on 4.1 is requiring only 6 Mbps while ‘Austin City Limits’ on 4.2 is running around 12 Mbps. Cartoons require less bandwidth.

    • This reply was modified 1 week, 4 days ago by boisebill.
    #51193
    mwdxer1
    Participant

    Rabbit Ears lists KATU, KOIN, KPTV, KRCW, and KPDX as fixed. But KGW and KOPB run a varied diginet. Is that correct?

    #51194
    DarkStar
    Participant

    RabbitEars.info is incorrect in that aspect.

    All the major broadcasters here in Portland are running variable bandwidths.

    #51195
    mwdxer1
    Participant

    Is there a site that gives the correct info? KGW and KOPB specs are varible on Rabbit Ears, but KATU, KOIN, KPTV, KRCW, and KPDX are not correct as they are not listed as varible. I live out at the coast and get 5 translators giving us 27 OTA channels from PDX (2/6/8/10/12/32/49.
    So that explains that 12.2 COZI that is listed at .9 mbps isn’t correct, as I wondered how they could get a decent picture using .9.
    Thanks for the info.

    #51196
    DarkStar
    Participant

    The only way to know for sure is to perform an analysis on the OTA signal.

    Using something like a USB tuner (I’ve used a WinTV-HD before: http://amzn.com/B015IL0FIW) and TSReader (https://www.tsreader.com/) will give you the instantaneous bitrate being consumed, but that won’t tell you the whole story about how the TV station is processing and encoding the video.

    Also, there is the capability for a TV station to “weight” a stream higher than another, so that while it is still variable bitrate one stream will have a higher priority to get “more bits” than the others. There isn’t a way to tell from the end-viewer though if that is happening with high certainty.

    As a visual example, here’s a screenshot of our video and audio bitrates for KATU right now. You’ll see the dramatic swings for the video bitrate and if you add all the video and audio bitrates together, it would be close to the 19.39 Mbps allowed — as one video feed doesn’t need as many bits, they get allocated to another video feed that could use them:

    https://bayimg.com/25e04e1b2f6ba6e0e69ba8584d428acf7421f32d.jpg

    #51199
    mwdxer1
    Participant

    Thanks. By your screen shot, KATU’s signal is 5 or above. That makes sense. As I was trying to figure out how the 720p pq could be that sharp is only using 3.4. I also did not know that the available bandwidth goes out to near 20. I read somewhere that an additional diginet could be added using the varying bandwidth. That is really cool. Thanks again for the screen shot.

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