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Source Input Format
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<p>Source Input Format (SIF) defined in <a href="/facts/MPEG-1/ewnQQLPD">MPEG-1</a>, is a video format that was developed to allow the storage and transmission of <a href="/facts/Digital_video/xsn9omqG">digital video</a>. </p> <ul><li><a href="/facts/625_lines/KXywE4Ps">625/50</a> SIF format (<a href="/facts/PAL/t8TugcxK">PAL</a>/<a href="/facts/SECAM/vexpud7W">SECAM</a>) has a resolution of 352 × 288 active pixels (half of PAL 704 × 576) [or 360 × 288 active pixels (half of PAL 720 × 576)] and a <a href="/facts/Refresh_rate/7mGJs7Dz">refresh rate</a> of 25 frames per second.</li> <li><a href="/facts/525_lines/NTPQFv9B">525/59.94</a> SIF Format (<a href="/facts/NTSC/HYWIvxCR">NTSC</a>) has a resolution of 352 × 240 active pixels (half of NTSC 704 × 480) [or 360 × 240 active pixels (half of NTSC 720 × 480)] and a refresh rate of 29.97 frames per second.</li></ul> <p>When compared to the <a href="/facts/Rec._601/rBCG7yEf">CCIR 601</a> specifications, which defines the appropriate parameters for digital encoding of TV signals, SIF can be seen as being reduced by half in all of height, width, frame-rate, and <a href="/facts/Chrominance/Ejtq4s5r">chrominance</a>. SIF video is known as a constrained parameters bitstream. </p><p>On <a href="/facts/Pixel_aspect_ratio/p8j8vWIa">square-pixel</a> displays (e.g., computer screens and many modern televisions) SIF images should be rescaled so that the picture covers a 4:3 area, in order to avoid a "stretched" look. So the computer industry has defined "square-pixel SIF" to be 320 x 240 active pixels (<a href="/facts/Graphics_display_resolution/zyMA9HHI">QVGA</a>) or 384 x 288 active pixels, with a refresh rate of whatever the computer is capable of supporting. To reach that the SIF content need to be "expanded" horizontally by 12:11 for PAL (<a href="/facts/Pixel_aspect_ratio/p8j8vWIa">PAR</a> = <a href="/facts/Display_aspect_ratio/hK5LYHN7">DAR</a> : <a href="/facts/Aspect_ratio_(image)/I3vbqVl3">SAR</a> = 4/3 : 352/288 = 12/11) and "reduced" horizontally by 10:11 for NTSC (PAR = DAR : SAR = 4/3 : 352/240 = 10/11). </p>