Bitrate of HDTV set-top box signals for FULL HD broadcasts

[Rajesh Singh]

My set-top box is Tatasky HD which is set to 1080i/60 Hz. Tatasky HD uses MPEG 4 for broadcasts. I want to capture video using Avermedia CV710 U3 and OBS Studio at best possible/passthru quality(Space is not a constraint) but at the same time I do not want to unnecessarily inflate the bit-rate and size. For that i need an estimate of current bitrate of video broadcasts. Also what CRF setting i should use to get pass-through. My CV710 proprietary software's max capablity is 1080p/30 FPS.

Also the input signal is Interlaced at 1080i/60 HZ which i understand to be 1080i /60 Fields per second(NOT Frames Per Second). Am i right ?Alo i crop the balck bars on OBS Studio scene from 1920x1080 to 1920x816 to remove black bars and then stretch it to full screen 1920x1080. Please suggest me the OBS Studio settings for pass-thru quality without UNECESSARILY INFLATING the bitrate.

[KarMa]

India is a former PAL country which used 50 fields per second, and as with most former PAL countries I would assume India still uses PAL rates in the digital realm too. So I would try to change your set up to work in either 25i or 50fps as I doubt any of your broadcasts are using NTSC rates. Using 29.970fps or 59.940fps won't drop any frames but will just create duplicate frames, causing weird jittering playback, and maybe require more bitrate.

Alo i crop the balck bars on OBS Studio scene from 1920x1080 to 1920x816 to remove black bars and then stretch it to full screen 1920x1080.

Playing back of 1920x816 on a modern 1080p TV should result in a maintained aspect ratio with the TV having black bars on the top and bottom, if you are literally stretching the image from 1920x816 to 1920x1080, then this will result in a massive aspect ratio error and make all the people look abnormally tall and skinny, along with anything else in the frame. Which is bad.


With x264, a CRF of 18 would probably be a good starting point for quality vs bitrate. Use a higher CRF for smaller size but worse quality, or a lower CRF for larger size and better quality. Using the slowest preset you can reliably encode with in real time without maxing out your CPU. So like Fast or maybe Very Fast (x264 preset). No matter what, you are going to lose quality with any re-encoding unless it's lossless.

If you are recording interlaced content with x264, then you also need the extra command

 --tff

Which enables interlaced encoding in x264 and denotes top field first.

[Rajesh Singh]

Hi KarMa, i have connected this Set-top box to a laptop whose display is 1080p 60 Hz. The settings on Tatasky HD set-top box has settings for both 1080i/50 Hz and 1080i 60 Hz which should correspond to the TV/monitor display. So i have selected 1080i/60 as per my monitor display.
I STILL need the answer for video BITRATE of HDTV broadcast signals so that i can set that in OBS Studio settings. Also how to take care of interlaced 1080i/60 Hz (which is 1080i 60 FIELDS PER SECOND and NOT Frames Per Second)]signals in Obs studio? Currently i am setting the output to 1080p/60 FPS(Field Per Second) after deinterlacing using yadiff2x.

[jagabo]

It doesn't matter what bitrate the source is, any time you recompress a video with lossy codecs there will be a loss of quality. So use the highest bitrate you can live with.

Also, the refresh rate of your monitor doesn't matter. Capture at the native signal rate, presumably 25i (the software may call it 50i, it's the same thing). Don't deinterlace while capturing.

[Rajesh Singh]

Hi KarmA, i tried your suggestions regarding 50 Hz PAL signals in India. On changing set-top box to 1080i 50 HZ and recording in Avermedia CV 710 Extreme Cap U3 in 1080p/25 FPS default detected setting, I get a frame drop every 1.02 seconds in Jriver Media Center with MadVR on my HP laptop display of 1080p/60 Hz. On setting the set-top back to 1080i/60 Hz and recording in Avermedia CV 710 Extreme CAP U3 default detected setting, the video plays with NO frame drops/repeats in Jriver(with video smooth option activated) .

ONE MORE Query: The Avermedia CV 710 proprietary software has a Recommended settings option on pressing detect button which gives these settings for Set-tp box connected via HDMI to Avermedia: Resolution:1080p, Frame Rate :30, Audio Bitrate: 128 kbps, Video Bitrate: 12Mbps. Do these config settings reflect the true parameters of Set-top box output via HDMI to Avermedia 710 capture card or are they just plain recommendations. The max recording capacity of card is 1080p/60 FPS. please advise me as i am confused over actual bitrate used by HDTV broadcasts.

Hi Jagabo, please give your inputs too. i am confused since uptill this date i was using 60 Mbps for recording . Was that unnecesary for HDTV signals recording because i read that Hauppage PVR card has outputs upto 13.5 Mbps only.

[usually_quiet]

ONE MORE Query: The Avermedia CV 710 proprietary software has a Recommended settings option on pressing detect button which gives these settings for Set-tp box connected via HDMI to Avermedia: Resolution:1080p, Frame Rate :30, Audio Bitrate: 128 kbps, Video Bitrate: 12Mbps. Do these config settings reflect the true parameters of Set-top box output via HDMI to Avermedia 710 capture card or are they just plain recommendations. The max recording capacity of card is 1080p/60 FPS. please advise me as i am confused over actual bitrate used by HDTV broadcasts.

If the Avermedia CV 710 Extreme CAP U3 can produce 1080p60 output from 1080i60 input, ideally you would attempt to capture 1080i60 as 1080p60, to produce a de-interlaced frame for every field. Capturing 1080i60 at 1080p30 would discard half the fields instead of de-interlacing all fields to full frames. You would also use a higher bit rate than 12Mbps for best quality, if possible.

I don't know for certain why Avermedia's software recommends 1080p30 at 12Mbps. I'm guessing it is because the card and its software are geared towards streaming game play, and these settings represents a limitation for some popular websites where gamers post their video. The only other reason for recommending 1080p30 would be that the Avermedia CV 710 Extreme CAP U3 is unable to de-interlace correctly and only captures half the fields while de-interlacing.

It is not important to know what bit rate Tata Sky uses for HDTV satellite broadcasts for the purpose of capturing. You should to capture at a relatively high bit rate regardless of the broadcast bit rate to reduce the compression artifacts introduced during capture.

[Rajesh Singh]

Hi usually_quiet, Avermedia gives max of 1080p/30 FPS with set-top box input . for other sources(for example the HDMI output of laptop fed back to Avermedia HDMI input) it gives 1080p/60 fps. I was using 40 MBPS for the last two years, to record movies and extract songs from them. Decided to try 60 MBps and deleted all the movie videos which can be recorded again. Confused between Avermedia Recentral and OBS-Studio. OBS Studio uses the concept of "scene" creation on which it puts out the source video and renders it. Does Avermedia and Hauppage also work similarly. I feel creating scene in OBS makes it an indirect method of capture and mught produce further loss of quality. Can somebosy comment on this ? Also is 1080p/60 FPS at 60 Mbps (at CRf value of 10 and max manageable setting of cpu preset superfast) OK to record HDTV via OBS Studio or am i being stuped with crf selection. because i cannot further lower the cpu preset without losing too much frames. What's your opinion of OBS Studio for recording HDTV via Avermedia CV 710 in comparison to Recentral software of Avermedia. The adv i feel is rhat OBS allows me to crop out black borders from the movie but IS OBS Studio an indirect way of recording as compared to Recentral of Avermedia ?

[Rajesh Singh]

But even Hauppage PVR HD has output of 13.5 Mbps max



On further digging, i read people quoting values ranging from around 16 Mbps as actual HDTV broadcast standard. I am not sure though but obviously it has to be less than 40 Mbps of Blu-ray

[usually_quiet]

Hi usually_quiet, Avermedia gives max of 1080p/30 FPS with set-top box input . for other sources(for example the HDMI output of laptop fed back to Avermedia HDMI input) it gives 1080p/60 fps.

Your told us that your set top box is configured to output 1080i60 video. Your laptop almost certainly outputs video over HDMI at 1080p60 rather than 1080i60. The Avermedia CV 710 Extreme CAP U3 can capture 1080p60 input correctly but apparently frame decimates 1080i60 to 1080p30 when deinterlacing.

Does Avermedia and Hauppage also work similarly.

No. The Hauppauge HD-PVR 2 encodes using its own on-board hardware, and can produce interlaced output from interlaced input, loosing no fields. From what you are telling us the Avermedia CV 710 Extreme CAP U3 drops half the fields when deinterlacing 1080i video, maybe even prior to output to the PC for software encoding. Since it always deinterlaces 1080i video, that makes it a poor choice for recording at that resolution. If you want better captures with the Avermedia CV 710 Extreme CAP U3, and it appears that your set top box doesn't output 1080p60, change the set top box to output at 720p60.

I was using 40 MBPS for the last two years, to record movies and extract songs from them. Decided to try 60 MBps and deleted all the movie videos which can be recorded again. Confused between Avermedia Recentral and OBS-Studio. OBS Studio uses the concept of "scene" creation on which it puts out the source video and renders it.

I feel creating scene in OBS makes it an indirect method of capture and mught produce further loss of quality. Can somebosy comment on this ? Also is 1080p/60 FPS at 60 Mbps (at CRf value of 10 and max manageable setting of cpu preset superfast) OK to record HDTV via OBS Studio or am i being stuped with crf selection. because i cannot further lower the cpu preset without losing too much frames. What's your opinion of OBS Studio for recording HDTV via Avermedia CV 710 in comparison to Recentral software of Avermedia. The adv i feel is rhat OBS allows me to crop out black borders from the movie but IS OBS Studio an indirect way of recording as compared to Recentral of Avermedia ?

The Avermedia CV 710 Extreme CAP U3 uses software to encode so both Avermedia Recentral and OBS-Studio are equally direct, if by direct you mean encoding only happens once. I never used either Avermedia Recentral or OBS-Studio so I cannot give you an opinion on which is better based on personal experience.

[usually_quiet]

But even Hauppage PVR HD has output of 13.5 Mbps max



On further digging, i read people quoting values ranging from around 16 Mbps as actual HDTV broadcast standard. I am not sure though but obviously it has to be less than 40 Mbps of Blu-ray

You should still capture at a higher bitrate than 16 Mbps if you can. Higher bitrate captures have fewer compression artifacts.

[Rajesh Singh]

Thanks Usually_Quiet for the detailed explanation.

[pandy]

Nowadays typical H.264 broadcast is around 10Mbps (between 8 and 12Mbps) - rarely on some broadcasters lineup one or two channels may be higher - around 14 - 16Mbps (usually premium channels for sport and movie events).

[Rajesh Singh]

Thanks pandy for the info