Pad 4:3 into 16:9

Problem

Transform a video file with 4:3 aspect ratio into a video file with 16:9 aspect ration by correct pillar-boxing.

Solution

ffmpeg \
    -i input_file \
    -filter:v "pad=ih*16/9:ih:(ow-iw)/2:(oh-ih)/2" \
    -c:a copy \
    output_file

Command syntax

ffmpeg

starts the command

-i input_file

path, name and extension of the input file

-filter:v "pad=ih*16/9:ih:(ow-iw)/2:(oh-ih)/2"

video padding

-c:a copy

re-encodes using the same audio codec

output_file

path, name and extension of the output file

Discussion

The video filter is specified by -filter:v. We advise to avoid the alias -vfilter and its abbreviation -vf as well. This resolution independent formula is actually padding any aspect ratio into 16:9 by pillar-boxing, because the video filter uses relative values for input width (iw), input height (ih), output width (ow) and output height (oh). Of course, in this formula the brackets are compulsory. The quotation marks are not mandatory, but we do recommend their usage.

For the specific transformation from SD into HD scaling is also needed.

The audio codec is specified by -codec:audio, which is usually abbreviated as -c:a (-codec:a or -c:audio are also possible). We advise to avoid the alias -acodec. For silent videos you can replace -c:a copy by -an; for video with sound you may choose to re-encode with another audio codec which is allowed by the container.

2020-07-15