Two very different results using the same settings (H.264 / Quicktime Pro)

[Jack Robertson]

I’m a bit confused, I have used Quicktime Pro (v7.1) to encode DV into H.264 for iPod and this particular video is 18 minutes long and came out looking very good with the following settings;

VIDEO: H.264 at 200kbps, Baseline Profile, 25fps, Auto Key Frames, 320x240 or 640x480, Multipass Best quality encoding.

AUDIO: AAC Audio at 96kbps, 24kHz sampling freq, Stereo.

However here is the twist…

When I use the same exact settings to encode just the 30 second opener (from the 18 minute video) the encoded opener looks bad and blocky!

Why? Same settings would make you assume that you should get a same or similar result, or am I wrong?

The reason I have tried encoding this 30 second opener is that I am trying to work out which settings work best on the iPod (another issue) and I don’t want to spend hours test encoding the full 18 minute video, as you know H.264 is SLOW to encode!

So can anyone help in regard to two very different results using the same settings?

Regards,
Jack

[Terence Murphy]

I suspect something wasn't exactly the same between your two renders. I think there's a menu option in Quicktime to look at the datarate of the encoded video -- I would check that to see if they were indeed encoded at the same data rates.

Also, what do you mean by "320x240 or 640x480"? At 200 kbps, 320x240 has a chance of looking good, but 640x480 is 4-times the data and will understandably look much worse.

If you're encoding a lot for the iPod, you might want to try VisualHub (www.visualhub.net), which will convert pretty-much anything-to-anything and is faster at H.264 encoding than Quicktime is.

-Terence

[William Hohauser]

Originally Posted by Jack Robertson

I’m a bit confused, I have used Quicktime Pro (v7.1) to encode DV into H.264 for iPod and this particular video is 18 minutes long and came out looking very good with the following settings;

VIDEO: H.264 at 200kbps, Baseline Profile, 25fps, Auto Key Frames, 320x240 or 640x480, Multipass Best quality encoding.

AUDIO: AAC Audio at 96kbps, 24kHz sampling freq, Stereo.

However here is the twist…

When I use the same exact settings to encode just the 30 second opener (from the 18 minute video) the encoded opener looks bad and blocky!

Why? Same settings would make you assume that you should get a same or similar result, or am I wrong?

The reason I have tried encoding this 30 second opener is that I am trying to work out which settings work best on the iPod (another issue) and I don’t want to spend hours test encoding the full 18 minute video, as you know H.264 is SLOW to encode!

So can anyone help in regard to two very different results using the same settings?

Regards,
Jack

Not to guess what your opener is like but openers frequently have many edits in them. This would overwhelm the codec which would have key frames spaced too infrequently to readjust the compression to the different images going by. The "Auto Key Frame" setting may not work as well as you need. Also dissolves are the hardest to compress.

If you have Final Cut Pro you could try to export using Compressor instead. That program will note edit points and alter the compression accordingly.

[Greg Boston]

Originally Posted by William Hohauser

Not to guess what your opener is like but openers frequently have many edits in them. This would overwhelm the codec which would have key frames spaced too infrequently to readjust the compression to the different images going by. The "Auto Key Frame" setting may not work as well as you need. Also dissolves are the hardest to compress.

If you have Final Cut Pro you could try to export using Compressor instead. That program will note edit points and alter the compression accordingly.

Exactly, William. I would maybe take it a step further and use compression markers in the FCP timeline to tell the encoder 'hands off' around dissolves and edits.

-gb-

[Jack Robertson]

--Terence;
Both the 18 minute and 30 sec files had the same datarate,

I can understand that at 200kbps the 640x480 would look worse but the the issue was that wether I do 320x240 OR 640x480 of both the full 18 mins and 30 sec opener the opener will look very bad compared to the full 18 min video which includes the opener at the head.

My preference is not to use VisualHub as I know Quicktime Pro should be able to encode this without problems, thanks for the suggestion though, will keep it handy.

--William;
I agree, the opener does have many edits in it and your suggestion of overwhelming the encoder sounds like the problem, I have done a few different test encodes of the 30 sec opener with different key frames instead of Auto and had better results but still not as good when I encoded the full 18 minute video.

--William & Greg;
I currently do not run Final Cut Pro and so cannot try that method of exporting from the timeline unfortunatelly.

MP4 / H.264 sure is not straightforward!

Jack

[William Hohauser]

Originally Posted by Jack Robertson

--William;
I agree, the opener does have many edits in it and your suggestion of overwhelming the encoder sounds like the problem, I have done a few different test encodes of the 30 sec opener with different key frames instead of Auto and had better results but still not as good when I encoded the full 18 minute video.

--William & Greg;
I currently do not run Final Cut Pro and so cannot try that method of exporting from the timeline unfortunatelly.

MP4 / H.264 sure is not straightforward!

Jack

No it certainly isn't. All these web codecs work better with tripod set interviews then hand held action.

Try to set the key frame interval to "All" or "Every Frame", I don't remember the exact term. That will create a very large file but it'll look better, hopefully.