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"Quality" / Fixed mbps / Downscaling – which is getting the best size/quality ratio in h.264?

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Leo Kann
"Quality" / Fixed mbps / Downscaling – which is getting the best size/quality ratio in h.264?
on Dec 28, 2015 at 2:40:35 pm

Hey,

My Situation: I am starting with a 7,8 GB prores422/mov file, exported from FCP. I need to compress it to a mp4 150-200 MB .

Now I am using MPEG Streamclip and there are the well known options:

1. Reduce the "Quality" (whatever that means) and try to hit the desired size
2. Set the MBPS to match the desired size (for me it would be very low, 3,7 MBPS)
3. Downscale the Material (its Full HD)

Whats bringing the best results here? One of them? A mix? I noticed, that the final size is not changing, when i alter the scale of the material while having a fixed mbps value ... does anybody know why that is?

Thank you for your help,
Leo


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Craig Seeman
Re: "Quality" / Fixed mbps / Downscaling – which is getting the best size/quality ratio in h.264?
on Dec 28, 2015 at 4:41:56 pm

It's been a while since I've used MPEGStreamclip but I believe Quality does nothing more than change the bit rate.

I wouldn't recommend using MEPGStreamclip because it's using Apple's old H.264 codec which was not very good.

It's better to use an x264 encoder (Handbrake) or Apple's AVFoundation improved H.264 codec (nearly as good as x264) found in the current version of Compressor.

It's not clear why you're targeting a file size. Under what professional circumstances are you faced with that limit? BTW this would be the antithesis of using "Quality" as a target.

Once you target your bit rate you'd want to use CABAC Entropy and High Profile for better quality at a given bit rate but that depends on the ability to play back the file. Key frame rate can have an impact but that depends on the source content and intent of the file.



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Leo Kann
Re: "Quality" / Fixed mbps / Downscaling – which is getting the best size/quality ratio in h.264?
on Dec 28, 2015 at 5:07:04 pm

Hi Craig,

thank you for the fast reply! I will be uploading the video in an application form that only accepts files no larger than 150MB. The video will then be watched in a small theatre / on peoples laptops.

MPEG-Streamclip does have a x.264 plug-in, at least mine has it. Would you still recommend using Compressor? On my computer Compressor is so much slower than Streamclip ...

And can you give me a hint to where I can enable CABAC and High Profile in the x.264 settings?

Best, Leo


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Craig Seeman
Re: "Quality" / Fixed mbps / Downscaling – which is getting the best size/quality ratio in h.264?
on Dec 28, 2015 at 5:44:44 pm
Last Edited By Craig Seeman on Dec 28, 2015 at 5:48:31 pm

[Leo Kann] "MPEG-Streamclip does have a x.264 plug-in,"

Yes there's an old (deprecated since it was Quicktime Frameworks based) version of x264 that should still work. It was developed by MyCometG3 (development ended in 2011. development ended for MPEGStreamclip in 2008)

This article shows the same codec (accessible by most old Quicktime based compressors) in Compressor. Next to" codeer_type" you can chose CABAC. Next to" b_frame_type" you can chose High Profile.

http://www.streaminglearningcenter.com/articles/encoding-with-the-x264-code...



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Ivan Myles
Re: "Quality" / Fixed mbps / Downscaling – which is getting the best size/quality ratio in h.264?
on Dec 28, 2015 at 6:45:48 pm

[Leo Kann] "I am starting with a 7,8 GB prores422/mov file, exported from FCP. I need to compress it to a mp4 150-200 MB .

Now I am using MPEG Streamclip and there are the well known options:

1. Reduce the "Quality" (whatever that means) and try to hit the desired size
2. Set the MBPS to match the desired size (for me it would be very low, 3,7 MBPS)
3. Downscale the Material (its Full HD)

Whats bringing the best results here? One of them? A mix?"


A mix of tactics will be required most likely. In addition to Craig's recommendations, consider downscaling the frame dimensions so that the resulting file size and bitrate correlate to at least 0.10 bits/pixel (preferably higher). The calculation is as follows:

bitrate(Mbps) * 1024 * 1024 / width / height / frame rate > 0.10

Therefore, for frame rates of 24-30fps and a bit rate of 3,7 Mbps you would want to reduce your full HD file to 1280x720. If you keep it at 1920x1080 the data rate per pixel would be equivalent to a YouTube video.


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Leo Kann
Re: "Quality" / Fixed mbps / Downscaling – which is getting the best size/quality ratio in h.264?
on Dec 28, 2015 at 9:18:58 pm

Thanks for the reply!

@Ivan: You also recommend downscaling for this material, when it will be projected to a medium sized cinema screen?

If the ratio is above 0.10, what will happen to the video?


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Ivan Myles
Re: "Quality" / Fixed mbps / Downscaling – which is getting the best size/quality ratio in h.264?
on Dec 28, 2015 at 10:43:03 pm

The higher the bitrate the better the picture quality. As bitrate decreases the pixels get grouped into larger blocks and the encoding gets more approximate / less accurate. This becomes especially problematic with frequent cuts and high motion footage.

For reference, YouTube videos come out to about 0.07 bits/pixel. Vimeo is a little higher, and Apple uses 0.12 bits/pixel. I consider 0.20-0.40 bits/pixel to yield good to very good quality in H.264. Blu-rays are encoded around 0.60-0.70 bits/pixel.


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