better source - 720p or 1080i

[rcrh]

So I've got an OTA antennae on my roof and I use WMC to record some TV shows. Once recorded I edit out the commercials and reencode them to 720p x264 files in an MKV container. One of the shows I've been watching has gone into syndication so I'm getting the opportunity to get some of the episodes I missed. The original, prime time airings were in 1080i and the syndicated reruns are in 720p. But both versions are ending up at about 4gig per 1 hour episode. My question is which source should make a better encode if I'm targeting the same 720p output. Other details from Media Info:


original: 1080i, 29.970fps, 12.3Mbps avg bit rate, 20.0Mbps max bit rate

syndication: 720p, 59.940fps, 12.8Mbps avg bit rate, 14.0Mbps max bit rate

output: 720p, 29.976fps, encoded with crf20

1) I know someone is going to say "encode both and watch them", but shouldn't there be a theoretically right answer?
2) my gut tells me that the same number of bits should look better when spread over a smaller aspect and therefore the 720p file should be better. But, I'm not sure how the frames per second factor in.

Any thoughts?

[sneaker_ger]

1) I know someone is going to say "encode both and watch them", but shouldn't there be a theoretically right answer?

No. You don't even know what encoders where used in the first place.

I'd just compare the output of the de-interlaced and resized 1080i version to your 720p capture. Encode the one that you think looks better, if you don't want to encode both sources just for a test.

[Atak_Snajpera]

output: 720p, 29.976fps, encoded with crf20
TV series are often 23.976 so you probably forgot to use Decimate function.

[gyth]

1) I know someone is going to say "encode both and watch them", but shouldn't there be a theoretically right answer?
If they are noticeably different then it doesn't matter which one is theoretically better, go with the one that is actually better.

Your real question should be whether it is worthwhile to reencode the 720p reruns when you already have the from 1080i originals. If reencoding the reruns doesn't look better, then don't do it.

[rcrh]

TV series are often 23.976 so you probably forgot to use Decimate function.

Oops. Fat fingers. I meant 23.976. I am using the decimate feature.

thanks.

[rcrh]

No. You don't even know what encoders where used in the first place.



I hadn't considered that the original mpeg's were OF COURSE encoded before broadcasting. DOH! It still "feels" like the same number of bits spread across a smaller resolution should look better.

[rcrh]

I'd just compare the output of the de-interlaced and resized 1080i version to your 720p capture. Encode the one that you think looks better, if you don't want to encode both sources just for a test.

I'm not considering the 720p CAPTURE as an option. It's MPEG-PS encoded video in an MPG container (just like the 1080i capture). I'll be reencoding one of these sources to a 720p x264 mkv file.

Thanks.

[Stereodude]

It depends on what the show is. Some is film based and can be IVTC'd meaning the 1080i likely has more detail. It also depends on much time / effort you want to put into deinterlacing. If you use something like QTGMC you could potentially end up with more detail in the 59.94fps 1080p output from it than is in the 720p version.

Now that we've discussed detail, the situation could be totally different with respect to mpeg-2 artifacts.

Ultimately, which one of the two sources looks better to you when played back? Use that one.

[rcrh]

Thanks to all.

Testing will continue and I'll hold on to both sources until I declare a winner!

[benwaggoner]

If the source was originally 1080p24, you should be able to get a pretty clean inverse telecine from the 1080i. However, if they use the same bitrate per channel, the 720p will probably look a lot cleaner, and certainly will be easier to work with since you don't need to inverse telecine/deinterlace or scale, and if you're using a deblocking decoder, you'll have fewer pixels for that to chew on.

If the 720p doesn't have a significantly lower bitrate than the 1080i, I bet it'll wind up being the optimum source for you all things being equal.

But yes, this is definitely a case where practice>theory, since there can be so many reasons why the streams look different beyond just 720p v. 1080i.