Average HDTV ATSC file size?

[dvasco]

Actually, what I should have asked is - What is the average filesize for a majority of the programs in HDTV? Or does it really vary that much? It seems weird that broadcasters would transmit each show at such a different bitrate and resolution. Does anybody know what the deciding factor for the broadcasters to determine which bitrate and resolution to transmit is? Why change from show to show, if they do?

[zaphod7501]

A big factor in bitrate would be multicasting. (resolutions are limited to some specific options unless you are on Satellite) The more subchannels the less bandwidth for each. There is a fixed maximum (19.something, I think ... too lazy to go look it up) that has to be divided up.

In my area, most HD ATSC takes a bit under 8Gb per hour (720p or 1080i) and SD ATSC takes 1.6Gb. While it will vary, I believe a good "rule of thumb" would be those figures to determine storage needs. If you are going to edit out commercials, then I would use 4.5Gb for HD and 1Gb for SD. (a DVD holds 4.38Gb as a reference for which Gb I'm referring to)

This also assumes that you are only recording a single program stream and no null packets. (most editing would remove the null packets also) This is a pretty standard option with most ATSC recording software. Those null packets are padding used in the transmission that can take up space but don't affect the bitrate. If they are recorded they can foul up calculations. ATSC is a variable bit rate system but transmitters are constant bitrate physical devices. Padding has to be added to make up the difference.

[dvasco]

Great info Zaphod. I also like your rule of thumb, which I had been looking for all along. Now that I think of it, if I were to get 250GB HDD HDTV doesn't seem to be too high a filesize for me, as long as I cut commercials immediately after recording, or if I delete the show immediately after watching it. Of course I would watch it at a different time that it records. That is one reason for PVRs.

[zaphod7501]

I am running four 80Gb drives (on three PCs) , edit immediately, and archive to DVD after watching. Space gets a little tight at times but is usually manageable. (two Hauppauge PVR250s for analog and a MyHD for HD. The Hauppauge HVR1600 is not trustworthy enough right now)

The most important condition for editing is at least two physical drives: read from one and write to the other. It can make the difference between a 5 minute save and 25 minutes. Even a little 15 or 20 Gb drive can be used as a shuttle. One other point, don't save files larger than 4Gb if you plan to save as data on a DVD. I found out the hard way that you can't write a 4.2Gb file to a DVD as data.

[dvasco]

Good to know also.