Questions About HDHomeRun HD Recording Quality

[jbarr]

HDHomeRun gives us 4 local HD stations over QAM cable through Charter Cable in Anderson, SC. So far, we're very happy with the lineup and the quality of the video. That said, I do have some questions about the actual recording quality of HD shows recorded using SageTV and HDHomeRun.

As a bit of a background, I read somewhere that HD recordings can sometimes be amazingly huge in size, like tens of GB per hour. But from my limited experience in playing with HDHomeRun over the past week, I found that almost all of my HD recordings are only about double the size of my analog recordings.

For example, I recorded a several 30 minute HD shows off of PBS using HDHomeRun, and the physical files range in size from 2.44GB - 2.66GB for 1/2 hour shows.

As a comparison, I recorded some 30 minute recordings from analog cable with a Hauppauge PVR-150 set to "DVD Long Play" recording quality, and the shows tend to be about 1.24GB in size.

And 1 hour HD shows seem to be sized at around 5.33GB per hour compared to analog shows which weigh in at about 2.02GB to 2.47GB per hour.

My speculation is that the source HD shows are just highly compressed, yielding the lower file sizes. And I think this is evident because the video quality, though quite good (significantly better than analog) doesn't seem to be as "hi-def" as I have seen elsewhere.

So, here are my questions:

1. Does SageTV's "Recording Quality" setting affect HDHomeRun recordings?
I'm guessing no. SageTV's recording quality settings control how the Hauppauge PVR-150's will record, but does the same hold true for HDHomeRun recordings? As I understand it, HDHomeRun simply passes the digital stream that it receives, and SageTV just records that stream.

2. What is the recording quality of HDHomeRun recordings?
I'm guessing that the answer is, "Whatever the source is sending" meaning that if Charter Cable send very compressed HD shows, then the file sizes will be smaller. Can someone clarify this?

3. What is your experience with HD recording sizes?

The really good news in all this is that though it seems that Charter's HD quality isn't as great as it could be, the fact that the file sizes are only double that of analog recordings means that recording HD content is much more doable, and it won't burn the storage space as I originally anticipated.

[Goodspike]

I think the answer to all your questions is yes.

I can't tell the difference between HD OTA and HD QAM through the HDHR and Comcast, but Comcast has very good HD (I've not been able to tell the difference when using other devices besides the HDHR). I think you're right that the file size is smaller, but from memory, I don't think my files sizes are as small as yours.

[Opus4]

Originally Posted by jbarr

1. Does SageTV's "Recording Quality" setting affect HDHomeRun recordings?
I'm guessing no. SageTV's recording quality settings control how the Hauppauge PVR-150's will record, but does the same hold true for HDHomeRun recordings? As I understand it, HDHomeRun simply passes the digital stream that it receives, and SageTV just records that stream.

Your "no" guess is correct, for digital streams -- SageTV does not re-encode digital streams. The recording quality setting only affects analog TV that the tuner has to encode.

2. What is the recording quality of HDHomeRun recordings?
I'm guessing that the answer is, "Whatever the source is sending" meaning that if Charter Cable send very compressed HD shows, then the file sizes will be smaller. Can someone clarify this?

Also correct -- it is entirely dependent on the quality used for the digital stream.

- Andy

[Sam]

Originally Posted by jbarr

I read somewhere that HD recordings can sometimes be amazingly huge in size, like tens of GB per hour.

What you are confusing this with is the uncompressed size of HD video, such as the threads which talk about trying to capture already decompressed HD video being sent via component to a display. That size would be huge, which is one of the obstacles in making it practical.

HD streams for OTA or QAM signals are already compressed at the source into a MPEG-2 stream. The image size and compression quality are dependent on how the source processes the signal, not the HDHR (or similar). The recording quality settings in Sage have no effect on the recording. About the thing you can impact is if the file is written as a transport stream (.ts) or viedo file (*.mpg).

[jkohn]

The quality is not dependent on Sage/HDHR, they're just saving the transport stream to disk without modification (well, Sage strips out any subchannels but that doesn't affect the HD channel's quality) The quality you get will depend on how much bitrate your local network is giving to the HD stream and how good their encoder is. 5-5.5GB/hour is not great, especially for 1080i and doubly so if using an older encoder. A couple of our local nets are using first-gen Harris encoders, and video quality really suffers for 1080i content on these encoders if the bitrate drops below 15-16mb/s average. And even at 17-18mb/s there's still plenty of artifacts in some scenes. Our CBS affiliate was at one time multicasting 3 sub-channels and giving only about 10-11mb/s to the 1080i feed. Video quality was terrible. They recently dropped the subchannels and the HD feeds is now getting about 17.5mb/s, and the quality is greatly improved. I've heard that the latest encoders can do pretty well with as little as 12mb/s, but I'm skeptical.

It's also possible that you cable company is re-encoding the channels at a lower bitrate before transmitting them, to save bandwidth. But I don't think too many cableco's are doing this because it requires additional investment in encoders on their end. In the case of our local networks the bitrate and quality is the same for cable and OTA.