Current video recording consumes too much memory

The official camera example (Widgets version) or declarative-camera example (QML version) can be used to reproduce the issue.

Procedures to reproduce:
1. Run the example
2. Start up task manager and find camera.exe or declarative-camera.exe
3. At idle, the memory consumption is ~40k KB.
4. During recording, the memory consumption hits ~200k KB.

Tested on FFMPEG too. Result is no better (~200k KB memory consumption during recording).

Someone else also provided test data. They are on Windows 10, and the data can be translated as:
1. Widget version example
Private memory: 53024 kb -> 249088 kb (4.7 times increase)
Commit memory: 80240 kb -> 382200 kb (4.8 times increase)
2. QML version application (not Qt example)
Private memory: 143388kb -> 340124kb (2.37times increase)
Commit memory: 190620 kb -> 499364 kb (2.52 times increase)