The audio codec is specified by -codec:audio, which may is usually as -c:a ( -codec:a or -c:audio are also possible). Note that today Rec. 709 is often used also for SD. If the luma coefficients are modified from SD video (according to Rec. 601) to HD video (according to Rec. 709), then you need to set the colour matrix by adding the filter colormatrix=bt601:bt709.
The formula pad=1920:1080:240:0 gives bit by bit exactly the same result if expressed as pad=1920:1080:(ow-iw)/2:(oh-ih)/2 by using relative values for input width (iw), input height (ih), output width (ow) and output height (oh). We use the Lanczos scaling algorithm ( flags=lanczos), which is slower but usually produces a better result than the default bilinear algorithm. Therefore this filter applies also for example to transform a 2K scan of a 4:3 film into a HD format for post-production and/or dissemination purposes. Note that the "scale=1440:1080" filter works for both upscaling and downscaling. Multiple filters are separated by a comma. The quotation marks allow to insert a space between the filters for readability. The quotation marks are not mandatory for these video filters, yet we advice to put multiple filters into quotation marks. We advise to avoid the alias -vfilter and its abbreviation -vf as well. The video filter is specified by -filter:v. Note that upscaling – including from SD to HD – does never increase the quality of the image. 1440 x 1080 pixel is the maximal size in 4:3 aspect ratio fitting into the 1920 x 1080 pixel of HD. We consider here a SD video file having square pixels.
c:a copy \ output_file Command syntax ffmpeg starts the command -i input_file path, name and extension of the input file -filter:v "scale=1440:1080:flags=lanczos, pad=1920:1080:240:0" video scaling and padding -c:a copy re-encodes using the same audio codec output_file path, name and extension of the output file Discussion Upscale and pillar-box a SD video file into a HD video file.
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