Some bitrate results: OTA vs Cable for HD locals

Discussion in 'TiVo Series3 HDTV DVRs' started by moyekj, Oct 6, 2007.

  1. Oct 6, 2007 #1 of 55
    moyekj

    moyekj Well-Known Member

    12,239
    897
    Jan 23, 2006
    Mission...

    Advertisements

    I've been meaning to do this for a while now and finally got some time this pm. Since I have Tivo S3 I can record both from Cox HD locals and from OTA broadcast of the same. So to test if Cox does much bit-rate shaping/degradation of the HD locals I recorded 30 min segments at the same time, 1 tuner recording Cox, other tuner recording OTA and then recorded the total file size of each (Tivo reports file sizes of each recording). Here are some results:
    Code:
    Cox, Orange County (Mission Viejo) headend
    STATION			OTA (GB)	CABLE (GB)	%DIFF
    CBS (1080i)		4.00		3.87		-3.2
    NBC (1080i)		3.96		3.84		-3.0
    ABC (720p)		3.47		3.52		1.4
    FOX (720p)		3.36		3.51		4.5
    
    So the Cox versions of 1080i channels are a little smaller, but surprisingly the Cox versions of the 720p are a little larger?? In any case based on this admittedly very small sample looks like Cox OC is not degrading the HD locals by much if at all.

    NOTE: There is some margin of error involved since the OTA version and Cox version are not exactly in sync (off by a few seconds), but that probably is negligible difference especially since these were 30 min samples.

    NOTE: Other factor is the 1080i OTA versions have complete PSIP information while the cable versions do not. The 720p cable channels do have full PSIP. Not sure how large PSIP information is compared to total file size but thought I should point that out.
     
  2. Oct 6, 2007 #2 of 55
    HDTiVo

    HDTiVo Not so Senior Member

    5,556
    0
    Nov 27, 2002
    Obviously your OTA signals come from local broadcast affiliates. Where does your cable co get its feed from?
     
  3. Oct 6, 2007 #3 of 55
    Joybob

    Joybob New Member

    581
    0
    Oct 2, 2007
    I guess we finally know what you do with your free time...
     
  4. Oct 7, 2007 #4 of 55
    moyekj

    moyekj Well-Known Member

    12,239
    897
    Jan 23, 2006
    Mission...
    The cable feeds are from the same affiliates (Los Angeles), but I think I was told once that the cable company gets the feeds via fiber optic link, not OTA. One would assume the feeds should be very similar if not identical, but I don't know for sure.
     
  5. Oct 7, 2007 #5 of 55
    moyekj

    moyekj Well-Known Member

    12,239
    897
    Jan 23, 2006
    Mission...

    Advertisements

    The reason I post this is I read quite a lot of claims in AVS forums and here that various cable companies degrade HD broadcasts compared to OTA, but I've never noticed much difference, hence I set out to study it on my own and this file size technique is pretty solid evidence. It really doesn't take much time or effort to do so I thought why not...

    Was kind of hoping others interested in this topic and with both OTA & cable feeds available may want to post their own results as a sort of informal survey.
     
  6. Oct 7, 2007 #6 of 55
    Joybob

    Joybob New Member

    581
    0
    Oct 2, 2007
    You could argue that their compression techniques are degrading the quality of the transmission without decreasing the bandwidth requirements?

    Similar file size doesnt mean it's the same quality?
     
  7. Oct 7, 2007 #7 of 55
    sfhub

    sfhub Well-Known Member

    2,883
    485
    Jan 6, 2007
    Can you compare just the video/audio streams using TSReader Lite?
     
  8. Oct 7, 2007 #8 of 55
    moyekj

    moyekj Well-Known Member

    12,239
    897
    Jan 23, 2006
    Mission...
    Well the problem there is that requires a PC, and since I only have 1 PC tuner I can't capture OTA & QAM at the same time like I can do with the Tivo. When TTG is enabled in November I suppose then I could transfer both streams to my PC from Tivo, but then the extracted streams will not be in Transport Stream format - they will likely be in encrypted .TiVo format as with S2 captures. There are programs to decrypt .TiVo to .mpg and then I suppose I could convert to .ts but as you can see that's quite a lot of hassle to do all that for this purpose...
     
  9. Oct 7, 2007 #9 of 55
    moyekj

    moyekj Well-Known Member

    12,239
    897
    Jan 23, 2006
    Mission...
    I highly doubt they are transcoding the HD feeds. Most often there is some bitrate shaping going on more than anything else, see:
    http://broadcastengineering.com/infrastructure/broadcasting_dtv_digital_cable/
     
  10. HDTiVo

    HDTiVo Not so Senior Member

    5,556
    0
    Nov 27, 2002
    While I do not have access to OTA to offer comparisons, I'd like to mention that I find some variability on CBS-cable. Most prime time recordings are around 5.25-5.5GB/hr while Sunday football has been around 6-6.25/hr this year.

    I've seen 4 1/3/hr to over 6/hr on ESPNHD. Bronx is Burning was generally the low end, while football the higher end.
     
  11. aaronwt

    aaronwt UHD Addict

    23,434
    1,204
    Jan 31, 2002
    Northern...
    Here Ota is the same size as Comcast which is the same size as FIOS on the same recording. And visually they all look the same.
     
  12. sfhub

    sfhub Well-Known Member

    2,883
    485
    Jan 6, 2007
    Have any friends with PC tuners in your area?
     
  13. moyekj

    moyekj Well-Known Member

    12,239
    897
    Jan 23, 2006
    Mission...
    Not worth all the hassle. I think comparing file sizes recorded on the S3 is accurate enough don't you think?
     
  14. George Webster

    George Webster New Member

    125
    0
    Apr 2, 2003
    I do all my recording with over the air broadcasts. Each show I record is on a digital channel and SD and HD seem to be all within 5.75 to 6.85 GB per hour. This means my 250 GB hard drive can only record 39.7 hours with an average of 6.3 GB per hour.

    I wish Tivo would stop advertising 300 hours with the series 3 - that is only for analog and with the quality set to the worst of the four settings.
     
  15. HDTiVo

    HDTiVo Not so Senior Member

    5,556
    0
    Nov 27, 2002
    What would you replace that with? They additionally quote HD recording time based on nearly 8GB/hr. What would you like to see?
     
  16. MickeS

    MickeS Active Member

    25,977
    24
    Dec 26, 2002
    I forgot about what they use for the estimated HD recording time. Since my cable stations use at the most around 6GB/hour (and looks like it too, sadly), I guess I have around 40 hours. Nice of TiVo to estimate it based on OTA recordings and not the compressed cable recordings...
     
  17. HDTiVo

    HDTiVo Not so Senior Member

    5,556
    0
    Nov 27, 2002
    The practical effect is you get 'this will be deleted on XXX' warnings that don't occur in reality close to that date. I'm always reestimating in my head whether I really have to worry - which of course really means I still don't have big enough hard drives. :D
     
  18. bkdtv

    bkdtv New Member

    7,902
    2
    Jan 9, 2003
    DC Metro Area
    Here are some average bitrates I measured:

    Off-air, Week of 9/04 - 9/09
    Code:
    [u][b]Network[/b][/u]   [u][b]Title[/b]	                  [/u]       [u][b]Minutes[/b][/u]  [u][b]Size(Gb)[/b][/u]  [u][b]Bitrate (Mbps)[/b][/u]
    [b]WRC       Tonight Show w/ Leno (9/4)       62	    7.51       16.54[/b]
    WBAL      Tonight Show w/ Leno (9/4)       62	    7.03       15.48
    
    WTTG      House (9/4)                      60       4.42       10.06
    WBFF      House (9/4)                      60       4.36        9.92
    
    WJLA      Grey's Anatomy (9/6)             61       5.31       11.89
    [b]WMAR      Grey's Anatomy (9/6)             61       5.65       12.65[/b]
    
    WUSA      U.S. Open Tennis (9/7)           60       7.24       16.48
    [b]WJZ       U.S. Open Tennis (9/7)           60       8.01       18.23[/b]
    WUSA      Jericho (9/7)                    60       7.11       16.18
    [b]WJZ       Jericho (9/7)                    60       7.91       18.00[/b]
    
    Verizon FiOS vs OTA Comparison
    Code:
    [u][b]Network[/b][/u]   [u][b]Title[/b]	                  [/u]       [u][b]Minutes[/b][/u]  [u][b]Size(Gb)[/b][/u]  [u][b]Bitrate (Mbps)[/b][/u]
    WRC-OTA   Tonight Show w/ Leno              62	    7.51       16.54
    WRC-FiOS  Tonight Show w/ Leno              62	    7.51       16.54
    WUSA-OTA  Redskins at Jaguars              170     19.80       15.90
    WUSA-FiOS Redskins at Jaguars              170     19.80       15.90
    
    Some programs recorded off Verizon FiOS...
    Code:
    [u][b]Title[/b]	                  [/u]      [u][b]Channel[/b]	     [/u]  [u][b]Minutes[/b][/u]  [u][b]Size(Gb)[/b][/u]  [u][b]Bitrate (Mbps)[/b][/u]
    Bronx is Burning                ESPN-HD           60	  7.50	     17.07
    College Football                ESPN-HD          180     23.34       17.70
    Alison Krauss & Union Station	Hdnet	         120	 15.39	     17.51
    Vince Gill & Friends            Hdnet            120	 15.50	     17.64
    Hunt for Red October            Hdnet Movies	 135	 17.44	     17.64
    Blazing Saddles                 Hdnet Movies	 100	 12.93	     17.65
    Layer Cake                      Hdnet Movies	 115	 14.85	     17.63
    Heroes                          NBC-HD	          60	  7.30	     16.61
    Naked Science                   NGC-HD            60	  7.56	     17.20
    The Company                     TNT-HD	         120	 15.11	     17.19
    The Recruit                     TNT-HD	         150	 18.96	     17.26
    
     
  19. Revolutionary

    Revolutionary Too sleepy for TV...

    575
    0
    Dec 1, 2004
    Virginia
    Man I wish we had HDNet channels on Cox. Universal-HD is the best we get, and the bitrate is more like 7.0Mbps.
     
  20. George Webster

    George Webster New Member

    125
    0
    Apr 2, 2003
    Well, I originally thought that the S3 would do 303 hours of NON HD content. That was before I discovered the setting that let you select the recording quality. There it says 52 hours on best quality but the S3 does not even provide that on NON HD content. All my OTA channels are digital and the recording quality setup screen says that those settings do not have any effect on digital channels. So I get 40 hours.

    Also, I can not understand why recording a NON HD digital channel takes up the same 5.8 to 6.8 GB per hour that it takes to record a HD progrram.

    HD = 1920 x 1080 = 2,073,600 pixels.

    SD = 640 x 480 = 307, 200 pixels

    So HD content has 6.75 times as much information in the signal. Seems to me they chose too high of a recording rate to render SD pictures and therefore wasted hard drive space.
     

Share This Page

spam firewall

Advertisements