The term anamorphic refers to a distorted image that appears normal when viewed with an appropriate lens. When shooting film or video, an anamorphic lens can be used to squeeze a wide image onto a standard 4:3 aspect ratio frame. During projection or playback, the image must be unsqueezed, stretching the image back to its original aspect ratio.
By default, 16:9 anamorphic video displayed on an standard monitor appears horizontally squeezed, meaning images look tall and thin. The advantage of this was in the past that producers could shoot wide-screen material using inexpensive equipment. Rescaling anamorphic video in order to see the entire wide screen frame on a standard definition 4:3 monitor is called letterboxing, and results in the loss of the maximum resolution available in the source footage. A wide screen (16:9) allows video-makers more room for creativity in their shot composition.
To check the support of anamorphic videos by different players, I created three mp4 videos from scratch, based on squeezed test pictures :
The following ffmpeg script creates a video from a squeezed source image towards a stretched widescreen video with a ratio 2.35:1.
-loop 1 ^
-f image2 ^
-i testbild_2_35_1_squeezed.jpg ^
-r pal ^
-vcodec libx264 ^
-aspect 235:100 ^
-crf 23 ^
-preset medium ^
-profile:v baseline ^
-level 3.1 ^
-refs 1 ^
-t 30 ^
The -aspect parameter handles the correct display aspect ratio (DAR). The MediaInfo tool shows that the video has 640×480 pixels, but an DAR of 2.35:1.
The VLC video player stretches the video based on the DAR. Videos with a wrong DAR in the metadata can be resized manually by changing the aspect ratio in the corresponding video menu.
More informations about anamorphic videos are available at the following links :