Movie: Constant quality Vs bit-rate

Apple Ipad 16gb tablet
July 19, 2010 at 09:44:09
Specs: Macintosh
The "Constant quality" option has been available for a while on Handbrake and you can choose this option over the regular and popular "Target size (MB):" or "Average bitrate (kbps/s): as a priority for best movie image quality.

From a DVD source select "Apple TV" or "iPhone & iPod Touch" presets and then on Quality / Constant quality race the percentage to 66% for the highest quality available on Handbrake and smooth playback on iPad, iPhone or iPod Touch.

Constant quality is what you might always choose as it makes more sense if your priority is the "best quality and adequate movie size". It does exactly what it says: The movie will keep its quality parameter "constant" and will vary the bitrate up to what it needs. Use the percentage bar up to 66%, beyond this you are just adding pixels and file size but not quality. If you are looking for a smaller file size lower the percentage.

With "Constant quality" you wont be able to calculate a resulting movie file size as the data rate varies from frame to frame.

In Handbrake If you choose the "Apple TV" or "iPhone & iPod Touch" presets you will notice the presets switches to "Constant quality".

Constant quality: image quality constant / data rate varies.
Average bitrate: data rate constant / image quality varies constantly
Target size: movie file size will prevail over quality and bitrate.

Keep the other presets.


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#1
July 19, 2010 at 13:37:58
For testing purposes I converted an original DVD movie using the settings I recommend here for the iPhone/iPod Touch, and later for the iPad and Apple TV:

Movie A:
"iPhone & iPod Touch" presets with constant quality @60%, default.
Movie size, 624.4 mb @ 870 kbit/s. 95 min

Movie B:
"iPhone & iPod Touch" presets with constant quality @66%, max.
Movie size, 896 mb @ 1251 kbit/s. 95 min

A 43 % increase in size for 10% increase in quality.

It is very hard to see the difference. The 66% quality better on the detail when scaling up to full screen on a 1920x1080 HD monitor.

Unless you demand the absolute best possible quality on highly detailed images, I can recommend the default settings for excellent results. Maybe even use up to 64% on any resolution you choose. The 10% increased quality is hard to appreciate.

Movie C:
"Apple TV" presets with constant quality @64%
Movie size, 1.75 Gb @ 1997 kbit/s. 95 min

Finally at 720x368 and 64% constant quality the difference is visible with the movies compared side by side. But the movie is on a higher resolution and is almost 3 times as big. Not the increase in quality manny would expect.

Using a DVD source I wont recommend to go beyond this settings for the iPad or even for a big screen TV set. Maybe a very sophisticated software will be able to extract more quality from a DVD, but I even compared some videos and movies from iTunes using the same settings and the movies are fairly simmilar.


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