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Problems compressing H264

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Ben Weinstein
Problems compressing H264
on Apr 3, 2011 at 11:53:54 am

- i have a new short film i need to compress to upload online. I do not care about the file size, I just want the best looking video. Last time I did this I had luck using QT conversion off my FCP timeline, setting H264 to "Best" single pass, 720P

one short film is 3:15 and 615MB
one short is 4:15 and 245 MB (and looks blocky)

any ideas why? I cannot go higher than "Best" but its clearly not giving me the same bitrate.

Ben


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Craig Seeman
Re: Problems compressing H264
on Apr 3, 2011 at 4:04:11 pm

When you use "Best" you're allowing the encoder to make the decisions on bit rate allocation. It will vary by content. Sometimes it doesn't make the "best" decisions although generally the data rates are so high that the resultant encode will look good. It'll may well be too high for playback in and of itself but it might be a good intermediary when sending to YouTube or Vimeo or any service that will re-encode the file again.

If you open the encoded files in Quicktime and use Window/Show Movie Inspector you'll see the resultant bit rate. Better though is use the free VideoSpec, which is not a player but a file analysis tool. It'll tell you a lot about the decisions the encoder made (or settings you chose).

http://www.apple.com/downloads/macosx/video/videospec.html

It'll give you an overview of what's different between the two encodes. In your case the only difference is likely to be the bit rate but at least you'll know what it is. You need to describe the content in detail or link to an example.

Once you get that information you'll venture into the skill and art of customizing settings. You might be better off using Compressor. Even Compressor is limited by professional standards though. You'll finding encoders like Telestream Episode or the equivalent will give you more tweaks.

You do need to describe your target in more detail. Are you uploading the file to be used as is or are you sending to a service such as YouTube or Vimeo for re-encode. This has a MAJOR impact on your decisions.

Also when you say an encode look blocky you leave out IMPORTANT information. "Look" implies you are viewing with something but you don't say what. Quicktime and VLC for example may not look the same. An old PPC Mac won't look the same as a MacPro because the CPU/GPU ability to decode will be different.

As implied above, the content is also important. That's where presets or "turning it up to 11" settings like "Best" fail. There is no one size fits all.

BTW you said you set to single pass. If you don't like the results of a setting you know you need to change something. Set to multipass. Make sure Frame reordering is enable (Apple's poorly worded description of B-frames).


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Ben Weinstein
Re: Problems compressing H264
on Apr 3, 2011 at 9:16:14 pm

Thank you!

I am seeing an improvement with setting target bitrate to 9999. can i just keep going up? can i make target 20K?

This is to post on FunnyOrDie.com they have a flash player. I do not care the size or bitrate, so long as it can be converted.


Shot on AF-100 - grainy blacks, had to use neat video. Cutting at 1080P at prores 422HQ .

screenshot:

http://imgur.com/ZuiNT


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Craig Seeman
Re: Problems compressing H264
on Apr 3, 2011 at 9:45:33 pm

Hmm, if you're sending 720p to be converted actually 5-10kbps should be enough.
True grainy blacks can certainly eat bits though. Basically compression is like "noise amplification" because it tends to preserve bits that change from frame to frame like noise. I wouldn't expect that to cause blockiness. At 720 it should be OK at 10kbps (9999 is about that).

Have you set it to multipass and frame reordering at that bit rate?



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Ben Weinstein
Re: Problems compressing H264
on Apr 3, 2011 at 9:50:53 pm

Thank you again.

I tried 20K and 15K and both were a decrease in size and quality.

I'm outputting that now. 9999 at multipass. What about keyframes? i have it at 24.


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Craig Seeman
Re: Problems compressing H264
on Apr 3, 2011 at 10:09:01 pm

Keyframes are one of those content based things. You could change it to every 150 frames (5 seconds at 29.97). I don't think that will have a radical difference given your high bitrates.

Something is fundamentally amiss if you're having blockiness at those bitrates. Either you're doing something wrong and it's not obvious from the info you're providing or there's something wrong in your source file. I can't imagine any content being helped much by going beyond 10,000kbps at 720p.

You REALLY need to reread my first post and answer my questions as you haven't done so in the entirety yet. There must be information you're not including. Sorry but at the bit rates you're describing just isn't likely to have problems such as blockiness.



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Ben Weinstein
Re: Problems compressing H264
on Apr 3, 2011 at 11:37:54 pm

The source clips have got real problems. The AF-100 was profoundly grainy in the 5-30 IRE range. I used Neat Video to clean it up. It worked, but theres no free lunch, its left some over simplified gradations from light to dark. and dark to dark. Its very subtle at full 1080 prores but when I compress them the colors become more simplified and look like banding. Like chips on a color chart representing stops from black to white. Blocky may have been the wrong word. This clip will be uploaded to a youtube-like site, it uses a flash encoder. the site also accepts Mpeg2. i own sorenson squeeze, is there any tips using the same concepts we discussed but with squeeze? Or should I use a more powerful Mpeg 2? I basically want to find a compression that has more values and more colors between black and white. I want LESS compression, the clip can be up to 1.5 GB. Basically I do not want to compress this video, I like the way it looks as a 5.85 GB file at pro res 422 HQ. You tips have helped tremendously. the latest compression looks that best at 293 MB multipass, 9999, frame reordering checked. Any tops pn a compression that reduces the colors less? for instance I like how it looks with Prores LT. But that is not accepted as a format by the flash encoder.


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Craig Seeman
Re: Problems compressing H264
on Apr 3, 2011 at 11:53:33 pm

So it does seem like the issue is in the source clips. You might have to re-evulate how heavily you cleaned up the grain vs the resultant banding. Compression can bring out the worst in a source.

H.264 is a much better codec than MPEG2. Squeeze using MainConcept's H.264 which is much better than Apple's. In fact Apple's H.264 is just about the worst one I've seen although the problems tend to be most visible at lower data rates. Perhaps your grain cleanup is exacerbating the codec's weakness.

You could use the same settings in Squeeze at the same 10,000 Kbps and you might get better results. I don't know the specific terminology Squeeze uses but generally you should try two or multipass variable bit rate. Key frames both natural and forced at 150 frames. Entropy CABAC. I'm not sure the exact B frame controls but you definitely want to use B frames. Generally try more B frames, more reference frames, Adaptive B frames if there's an option for it. Since your source is progressive make sure deinterlace is off/disable. I use Episode so someone who uses Squeeze regularly may want to provide more details.



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