[FFmpeg-user] Quicktime reports diiferent width than ffmpeg
marc at hallmarcwebsites.com
Fri Nov 11 19:17:35 CET 2011
> -----Original Message-----
> From: ffmpeg-user-bounces at ffmpeg.org [mailto:ffmpeg-user-
> bounces at ffmpeg.org] On Behalf Of Dave Bevan
> Sent: Friday, November 11, 2011 12:09 PM
> To: FFmpeg user questions and RTFMs
> Subject: Re: [FFmpeg-user] Quicktime reports diiferent width than ffmpeg
> >> >Anyone know why QuickTime would report a different width for an .mov
> >> than ffmpeg does?
> >> Check aspect ratio flags (DAR/PAR etc). If I remember correctly, QT
> >> reports,
> > for example, 1024x576 for anamorphic 720x576.
> >Stream #0.0(eng): Video: svq3, yuvj420p, 648x486, 1577 kb/s, SAR
> >43185:32768 DAR 14395:8192, 29.91 fps, 29.95 tbr, 29954 tbn, 29954 tbc
> >the wxh shows ~4:3 SAR is also ~4:3 yet DAR is ~16:9 the actual video
> >plays at ~16:9 or 854x486 the only dimension reported here evenly div
> >by 4 is 648 which makes me think ffmpeg isn't so much reading the
> >dimensions as it is calculating them?
> >Still learning
> So your DAR (display aspect ratio) is 14395:8192. Take that with your
> and you get:
> (14395 / 8192) * 486 = 854.000244....
> So, it's working exactly as expected, with QT doing exactly what's asked
of it -
> to take 648x486 video and display using the DAR defined in the wrapper,
> giving you 854x486.
> Basically, video is stored in square pixels - in your case 648x486 - so
> pixels per frame. Pixels can have DAR applied and it's down to display
> to STRETCH the original video WIDTH at the DAR ratio to give the final
> In European TV land, all [digital] video of Standard Definition is
> down video pipes that are 720x576 in size. Further, there is padding
> which actually means the "active picture" is contained in 702x576 pixels,
> 9px padding on left/right. When WIDESCREEN was introduced, none of the
> physical equipment changed. Simplistically, all that occurred was flagging
> video with a 16:9 flag. It meant that when a camera captured video, it
> a "viewport" that was 16:9 aspect ratio and scaled/squashed the horizontal
> pixels seen into the 702x576 box. Then the video travelled around all it's
> pipes, vision mixers etc, eventually to TV transmitters into your house
> into your TV, all squashed into the 702x576 box. A side-band flag tells
> to stretch the video picture back to be shown to you as widescreen. That
> "display" 4:3, 16:9 button on your TV remote is simply overriding the
> from the TV station saying the picture should be shown in widescreen, vs
> old 4:3 aspect ratio.
> Many people thought that the introduction of 16:9 meant better pixels, but
> in fact it means less quality, because the width of what you see is being
> stretched more, rather than less.
> In HD, things are different of course - the signal [usually] transported
> TV is 1920x1080, though it can be 1440x1080, 1280x720, or even 960x720.
Am I correct in assuming this is true for any container not just mov?
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