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ext/dv/gstdvdec.c: Change the pixel aspect ratio of dvdec output to reflect a different dubious internet source. Add ...

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Original commit message from CVS:
2005-01-28  Andy Wingo  <wingo@pobox.com>

* ext/dv/gstdvdec.c: Change the pixel aspect ratio of dvdec output
to reflect a different dubious internet source. Add a reference
and some commentary.
This commit is contained in:
Andy Wingo 2005-01-28 17:35:13 +00:00
parent 057004e7e3
commit 7fb19363a6
2 changed files with 51 additions and 8 deletions
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6
ChangeLog
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@ -1,3 +1,9 @@
2005-01-28 Andy Wingo <wingo@pobox.com>
* ext/dv/gstdvdec.c: Change the pixel aspect ratio of dvdec output
to reflect a different dubious internet source. Add a reference
and some commentary.
2005-01-28 Ronald S. Bultje <rbultje@ronald.bitfreak.net>
* gst/playback/gststreamselector.c: (gst_stream_selector_init),

53
ext/dv/gstdvdec.c
View file

@ -28,6 +28,43 @@
*/
#include "gstdvdec.h"
/* DV output has two modes, normal and wide. The resolution is the same in both
* cases: 720 pixels wide by 576 pixels tall in PAL format, and 720x480 for
* NTSC.
*
* Each of the modes has its own pixel aspect ratio, which is fixed in practice
* by ITU-R BT.601 (also known as "CCIR-601" or "Rec.601"). Or so claims a
* reference that I culled from the reliable "internet",
* http://www.mir.com/DMG/aspect.html. Normal PAL is 59/54 and normal NTSC is
* 10/11. Because the pixel resolution is the same for both cases, we can get
* the pixel aspect ratio for wide recordings by multiplying by the ratio of
* display aspect ratios, 16/9 (for wide) divided by 4/3 (for normal):
*
* Wide NTSC: 10/11 * (16/9)/(4/3) = 40/33
* Wide PAL: 59/54 * (16/9)/(4/3) = 118/81
*
* However, the pixel resolution coming out of a DV source does not combine with
* the standard pixel aspect ratios to give a proper display aspect ratio. An
* image 480 pixels tall, with a 4:3 display aspect ratio, will be 768 pixels
* wide. But, if we take the normal PAL aspect ratio of 59/54, and multiply it
* with the width of the DV image (720 pixels), we get 786.666..., which is
* nonintegral and too wide. The camera is not outputting a 4:3 image.
*
* If the video sink for this stream has fixed dimensions (such as for
* fullscreen playback, or for a java applet in a web page), you then have two
* choices. Either you show the whole image, but pad the image with black
* borders on the top and bottom (like watching a widescreen video on a 4:3
* device), or you crop the video to the proper ratio. Apparently the latter is
* the standard practice.
*
* For its part, GStreamer is concerned with accuracy and preservation of
* information. This element outputs the 720x576 or 720x480 video that it
* recieves, noting the proper aspect ratio. This should not be a problem for
* windowed applications, which can change size to fit the video. Applications
* with fixed size requirements should decide whether to crop or pad. If you
* decide to crop, the videocrop element might be useful to you.
*/
#define NTSC_HEIGHT 480
#define NTSC_BUFFER 120000
#define NTSC_FRAMERATE 30000/1001.
@ -36,15 +73,15 @@
#define PAL_BUFFER 144000
#define PAL_FRAMERATE 25.0
#define PAL_NORMAL_PAR_X 16
#define PAL_NORMAL_PAR_Y 15
#define PAL_WIDE_PAR_X 64
#define PAL_WIDE_PAR_Y 45
#define PAL_NORMAL_PAR_X 59
#define PAL_NORMAL_PAR_Y 54
#define PAL_WIDE_PAR_X 118
#define PAL_WIDE_PAR_Y 81
#define NTSC_NORMAL_PAR_X 80
#define NTSC_NORMAL_PAR_Y 89
#define NTSC_WIDE_PAR_X 320
#define NTSC_WIDE_PAR_Y 267
#define NTSC_NORMAL_PAR_X 10
#define NTSC_NORMAL_PAR_Y 11
#define NTSC_WIDE_PAR_X 40
#define NTSC_WIDE_PAR_Y 33
/* The ElementDetails structure gives a human-readable description
* of the plugin, as well as author and version data.