diff options
Diffstat (limited to 'ext/dv')
| -rw-r--r-- | ext/dv/gstdvdec.c | 53 |
1 files changed, 45 insertions, 8 deletions
diff --git a/ext/dv/gstdvdec.c b/ext/dv/gstdvdec.c index 0bcff81b..03808d1d 100644 --- a/ext/dv/gstdvdec.c +++ b/ext/dv/gstdvdec.c @@ -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. |