[SOLVED] Video aspect ratio, SAR, DAR

GPGAgent · 12-27-2021, 11:53 AM

I'm confused - not unusual for me I know

I've examined this video with ffprobe, ffmpeg cropdetect, mediainfo and a screencap from vlc:

Code:

ffprobe TalkingPictures_TV-05192021-1730.mts 
 Stream #0:0[0x32b]: Video: mpeg2video (Main) ([2][0][0][0] / 0x0002), yuv420p(tv, top first), 544x576 [SAR 24:17 DAR 4:3], 25 fps, 25 tbr, 90k tbn, 50 tbc

ffmpeg  -ss 1:00 -i TalkingPictures_TV-05122021-1400.mts -t 1 -vf cropdetect -f null - 2>&1 | awk '/crop/ { print $NF }' | tail -1
crop=544:560:0:10

mediainfo TalkingPictures_TV-05192021-1730.mts 
Width                        : 544 pixels
Height                       : 576 pixels
Display aspect ratio         : 4:3
Active Format Description    : Full frame 16:9 image

From the VLC screenshot - Properties - image 768x576 pixels  4:3

Only the screencap properties of the png file and the DAR setting makes any sense - it does have an aspect ratio of 4:3.

I don't see where 544 x 576 or 544 x 560 get calculated.

Can someone smarter than me explain how these other numbers fit?

business_kid · 12-27-2021, 12:18 PM

/Just guessing wildly.

It looks like total nonsense in the information output, and is definitely not 16:9 but nearer 4:3.

I'm an ex-tv repair man back in the days of analog tv, when hardware was expensive and labour was cheap. Those numbers in the 500s (544 particularly) seem reminiscent of some NTSC statistic? I'm on PAL here and there was also Secam, all different. They used Analogue TVs with tubes instead of flatscreen and had large invisible portions on the horizontal.

I'm thinking 544 was the horizontal information width on NTSC? - the visible portion. The 576 is for the birds, but they might have done interlaced. There was very small invisible portions top & bottom. It was mainly on the sides, because the dot travelled faster left to right than up & down.

GPGAgent · 12-27-2021, 12:24 PM

Quote:

Originally Posted by business_kid

/Just guessing wildly.

It looks like total nonsense in the information output, and is definitely not 16:9 but nearer 4:3.

I'm an ex-tv repair man back in the days of analog tv, when hardware was expensive and labour was cheap. Those numbers in the 500s (544 particularly) seem reminiscent of some NTSC statistic? I'm on PAL here and there was also Secam, all different. They used Analogue TVs with tubes instead of flatscreen and had large invisible portions on the horizontal.

I'm thinking 544 was the horizontal information width on NTSC? - the visible portion. The 576 is for the birds, but they might have done interlaced. There was very small invisible portions top & bottom. It was mainly on the sides, because the dot travelled faster left to right than up & down.

Cheers, it's UK TV that I recorded with a cheap chinese set tip bax that records to a USB stick, being Chinese they totally ignore any DRM settings so the video it saves is in mts format. And I'm sure it's 4:3 format.

business_kid · 12-28-2021, 06:15 AM

UK tv I am familiar with.

I Can confirm that you can ignore the output. The UK and Ireland doesn't issue a dpi spec, but it was close to 640×480 @50Hz interlaced last time I did the math. Pal is interlaced vertically, so you get lines 1,3,5, etc. on one frame and 2,4,6 next time. The actual picture refresh is 25Hz but it's acceptable because of interlacing and persistence on the tv tubes, now mimicked in flatscreen monitors.

Ignore the numbers that don't make sense, and use the ones that do. That's all you can do. Be glad the thing works at all, and if it works, don't fix it