Thumbnail of the video is too small in messaging app

[TarotChen]

Test Environment:
$ system-image-cli -i
current build number: 255
device name: arale
channel: ubuntu-touch/rc-proposed/meizu.en
last update: 2016-02-25 02:26:47
version version: 255
version ubuntu: 20160224
version device: 20160111-51982fc
version custom: 1452441600

Steps:
1.Launch messaging-app
2.Send a MMS with a video file with resolution 150X84
3.Send second MMS with a video file with resolution 800X600
4.Observe the thumbnails in messaging-app

Expected result:
The thumbnail of video file is displayed correctly

Actual result:
The thumbnail of 150X84 video is too small, see attached pic