File Size of S3 Recordings (experiment results)

[astrohip]

I was curious about the file size of S3 recordings, so I ran an experiment. In particular, I wanted to see how SD compared to HD, and what affect recording quality has on file size. Had what I consider to be some strange results. Maybe some of you can shed some light on this.

I wanted to use one show, to give this test some consistency. I picked 24, as it is syndicated all over the place. I have Time Warner cable in Houston. Cable cards on an S3 TiVo. All one hour episodes.

Network (channel #) - file size - comments
WGN (54) - 1.15GB
KPRC (312) - 5.82GB - local NBC affiliate
A&E (23) - 3.22GB - best quality
A&E (23) - 2.42GB - high quality
Fox (309) - 4.57GB - HD broadcast

All of the above were SD broadcasts, 4:3. Except Fox, was HD and 16:9 (the Fox was Monday night's new episode; the rest were syndicated showings). On the KPRC and WGN recordings, I was *not* offered a recording quality. On the A&E broadcasts, I *was* able to choose a quality; so I did one Best and one High.

* Why do some cable channels let you choose quality (A&E), and others not?

* Why is the WGN size so much smaller than either of the A&E sizes?

* (the big question) Why is the KPRC broadcast (that's our local NBC affiliate) so much larger than the Fox-HD broadcast? I have confirmed by viewing them that the KPRC was an SD 4:3, not an HD.

PS: My Recently Deleted Folder is up to 121 entries. It still has the first show I deleted since the 750GB was installed, so I have yet to fill the disk. My Now Playing has about 50 shows in it. 75% HD, the rest SD.

[Krellion]

* Why do some cable channels let you choose quality (A&E), and others not?This is most likely due to your cable company not simulcasting all the "non-digital" channels (numbers below 100). Some are sent to you as digital, but others (like A&E) haven't been moved over yet and are still analog.
* Why is the WGN size so much smaller than either of the A&E sizes?With most SD digital channels, they're compressed at the cable company instead of on your TiVo, so you're comparing the ability of expensive encoders to the low-cost one in the TiVo. Of course the cable company's encode will be better quality and smaller (they can also avoid a lot of the analog noise and such that your TiVo has to deal with).
* (the big question) Why is the KPRC broadcast (that's our local NBC affiliate) so much larger than the Fox-HD broadcast? I have confirmed by viewing them that the KPRC was an SD 4:3, not an HD.Not entirely sure about this. Are you sure that it's just SD and hasn't been upconverted by your NBC affiliate and sent as HD? A quick way to check would be to change the Aspect mode to "Full". If it is SD, it should be stretched to fit your TV screen and not look correct.

[jchapman]

Based on what you've said and my own experience:
WGN was a normal digital SD broadcast
KPRC was not a normal digital SD broadcast
A&E was an normal analog SD broadcast at best
A&E was an normal analog SD broadcast at high
Fox was a normal digital HD broadcast

This is why simulcasting digital and analog is great if your cable company does it; if you're getting your SD digitally it's taking up less space for the same or better quality. I have no idea what's going on with KPRC; are all the hourlongs on that station similar in size? If you get info, was it sent as 480i? It would make more sense if it was 720p or 1080i; in that case it was broadcast in HD, but they only sent the 4:3 SD picture.

[wackymann]

Most likely KPRC is transmitting 1080i at a higher bitrate than Fox's 720p. HD locals generally DO NOT turn down to 480i for SD shows. They just upsample the show to 1080i (or 720p) and add black (or grey) bars to the sides.

If you are concerned about space, you should record the digital non-HD channel (if it exists on your system). It sounds like you probably DON'T have that option - since your A&E is analog, I'm guessing your nonHD locals are also analog.

[CraigHB]

I've found the best SD quality and least disk space consumption with digital broadcasts (all HD broadcasts are digital). The TiVo does not encode those transmissions. It stores the digital stream as it receives it. That's why there's no recording quality setting. Disk space consumption is entirely dependant on what the broadcaster does on their end. DirecTV TiVo users are familiar with this. Since DirecTV digitally encodes their analog sources before they broadcast them, DTiVos do not have a recording quality setting either. However, DirecTV encoding is a bit on the over-compressed end of things. SD via digital cable and digital OTA is great. The quality is excellent and the disk space consumption is much lower. I wish I could get all my SD channels that way.

A 4:3 show on a HD channel is still HD as far as the digital stream goes. Here's your results in terms of broadcast format;

WGN (54) - 1.15GB; 480i, digital
KPRC (312) - 5.82GB; 1080i or 720p
A&E (23) - 3.22GB; 480i, analog, best
A&E (23) - 2.42GB; 480i, analog, high
Fox (309) - 4.57GB; 1080i or 720p