Why FFmpeg print SAR instead of PAR?

Question

If my knowledge is correct, SAR (Storage Aspect Ratio) is the ratio of pixel dimensions. For example, a 640 × 480 video has a SAR of 640/480 = 4:3.

Whereas PAR (Pixel Aspect Ratio) is ratio of pixel height and width, and most of modern videos have square PAR (1:1).

But when I tried to check it with ffmpeg -i I got square SAR instead of square PAR for all test videos.

Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 1758 kb/s, 24.99 fps, 25 tbr, 25 tbn, 50 tbc
Stream #0:0(und): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p, 540x360  [SAR 1:1 DAR 3:2], 386 kb/s, 25 fps, 25 tbr, 25 tbn, 50 tbc
Stream #0:0(und): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p,  450x360 [SAR 1:1 DAR 5:4], 328 kb/s, 25 fps, 25 tbr, 25 tbn, 50 tbc

Is it ffmpeg bug or my mistake?

Answer 1

SAR (Sample Aspect Ratio) is the same as PAR (Pixel Aspect Ratio).

These two terms are used interchangeably. They mean the ratio between the width and the height of individual pixels.

In contrast, DAR (Display Aspect ratio) is the ratio between the width and the height of the full image.

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Notes:

SAR - All modern devices have it 1:1; old devices — mainly from the analogic-numeric transition era — used non-square pixels.

DAR - examples: For SVGA it is 4:3, for QWXGA it is 16:9.

Answer 2

As it turned out, ffmpeg uses different notations

• SAR for Sample Aspect Ratio
• DAR for Display Aspect Ratio