Bitrate for SDTV

[Polypro]

Is there an approximate bitrate for analog cable broadcasts? I assume recording at a higher bitrate wouldn't help with quality and just waste space?

OTA HDTV: Same question (I know it's ~19Mbs), but would MPEG2 Max Quality give a better picture?

Thanks,

P

[Opus4]

For analog recordings, the bitrate you should use just comes down to the one you are satisfied with. That sounds like a non-answer, but different people have different criteria, and sometimes different criteria for different shows. The higher rates are good when there is lots of motion, for example. Personally, I still see artifacts at 2 GB/hr, so I ended up using one of the 3 GB/hr settings -- at that rate, I can't really tell the difference between live TV & a recording.

For HDTV, the recording rate is meaningless because the OTA broadcast is simply captured & saved to disk -- there is no encoding being done on the PC.

- Andy

[Polypro]

Thanks Andy. I kind of figured that the HDTV setting didn't matter, just wanted to check. Yeah, I tried 2GB/Hr and it didn't look too good. To me, MPEG Max looked the same as DVD Standard, so I think that would just waste space with no quality improvement.

P

[stanger89]

Analog broadcasts take bandwidth equivalent to about 20Mbps or so (HD is piped in a "normal" analog bandwidth).

[Polypro]

Thanks for the info stanger.

P

[stevech]

Analog SD TV is a 6MHz signal. The signal yeilding the resolution (not colors) in NTSC is less than 3MHz.
It's too bad that digital video is so inefficient.
It's good if you have gigabit speeds.

The same is true for VoIP: it takes 2 X 64Kbps to do decent VoIP with today's stuff. A telephone uses a 3KHz channel! Cell phones use about 30Kbps (simplifying).

[nielm]

TV may use a 6Mhz signal, but when digitising that signal, how many levels do you use? And, when digitising an analogue signal, you need to sample at at least twice the maximum frequency.

So to do a straghtforward digitization of a TV signal, so you need to sample at 12 Million samples/sec... 8bits/sample, and you get 96Mbps...

Or if you consider an uncompressed 24bpp 640x480 30frame/sec video stream...640x480x30x24=210Mpbs.

Mpeg2 compressed video uses 8Mbps... I would say that it is pretty efficient If you had good signal quality, you could fit several digital channels in the space of 1 analogue!

Similarly for an analogue phone: 3Khz - digitise at at least 6Ksamples/sec at 8 bits/sample and you get at least 48Kbit/sec (in practice, 56 or 64Kbps are used... thats how modems manage to get 30-40kbps down an analogue phone line.

[stanger89]

Originally Posted by nielm

Mpeg2 compressed video uses 8Mbps... I would say that it is pretty efficient If you had good signal quality, you could fit several digital channels in the space of 1 analogue!

More like 2Mbps if you're using a good encoder like the cable/sat companies