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I am writing some unit-tests for a software that does some work with videos. To do so, I need a programmatically generated video file that is both small and legitimate in that it is actually a sensible video from the point of view of a codec.

An idea that came to mind was to produce a video of a single frame of a solid color. I have tried that in Apple Motion. However, the file still ended up being about 8KBs. That is not so big, but I am wondering if one can do better.

Do you have any advice on how? I would be happy with MP4 container.

To give you an example of what I may be after, here is a list of HEX codes that produces a small but valid .PNG image:

png_hex = ['\x89', 'P', 'N', 'G', '\r', '\n', '\x1a', '\n', '\x00',
           '\x00', '\x00', '\r', 'I', 'H', 'D', 'R', '\x00',
           '\x00', '\x00', '\x01', '\x00', '\x00', '\x00', '\x01',
           '\x08', '\x02', '\x00', '\x00', '\x00', '\x90',
           'w', 'S', '\xde', '\x00', '\x00', '\x00', '\x06', 'b', 'K',
           'G', 'D', '\x00', '\x00', '\x00', '\x00',
           '\x00', '\x00', '\xf9', 'C', '\xbb', '\x7f', '\x00', '\x00',
           '\x00', '\t', 'p', 'H', 'Y', 's', '\x00',
           '\x00', '\x0e', '\xc3', '\x00', '\x00', '\x0e', '\xc3',
           '\x01', '\xc7', 'o', '\xa8', 'd', '\x00', '\x00',
           '\x00', '\x07', 't', 'I', 'M', 'E', '\x07', '\xe0', '\x05',
           '\r', '\x08', '%', '/', '\xad', '+', 'Z',
           '\x89', '\x00', '\x00', '\x00', '\x0c', 'I', 'D', 'A', 'T',
           '\x08', '\xd7', 'c', '\xf8', '\xff', '\xff',
           '?', '\x00', '\x05', '\xfe', '\x02', '\xfe', '\xdc', '\xcc',
           'Y', '\xe7', '\x00', '\x00', '\x00', '\x00',
           'I', 'E', 'N', 'D', '\xae', 'B', '`', '\x82']
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    This almost sounds like a job for code golf. codegolf.stackexchange.com – stib Nov 12 '19 at 17:20
  • I am familiar with code golf and even played some. How do you reckon this is a good fit? :-) – MadPhysicist Nov 12 '19 at 21:34
  • Well if you consider writing a h.264 file could be considered writing code—it's a piece of code that gets rendered to produce an image, juts like a piece of html gets rendered to produce a web page. Maybe a stretch, and I don't know how many golfers would be familiar with the intricacies of h.264, but it's trying to produce the smallest valid piece of code. – stib Nov 12 '19 at 23:43
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A one frame H264 stream would have to consist of an intra-coded frame, so there is a size floor in effect.

This ffmpeg command produces a 1.7 kiB file

ffmpeg -f lavfi -i color=blue:s=1280x720 -vframes 1 out.mp4

You can save ~200 bytes by lowering the resolution.

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  • Out of interest, why blue? – stib Nov 12 '19 at 17:21
  • No reason in particular. – Gyan Nov 12 '19 at 17:52
  • I tested it and found that if you use white instead you save 6 bytes. – stib Nov 12 '19 at 23:46
  • There's a lot of plain text in the header, e.g. there's a copyright notice and a URL H.264/MPEG-4 AVC codec - Copyleft 2003-2019 - http://www.videolan.org/x264.html. I tried just yeeting it out with a text editor but the resultant file wouldn't play. I'd say you could optimise it a bit more by studying the mp4 file format more than I have time to do: xhelmboyx.tripod.com/formats/mp4-layout.txt – stib Nov 13 '19 at 0:07
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    That's not MP4 data, but SEI unit inserted by the x264 encoder. Yeah, that could be filtered out. I wasn't trying to absolutely optimize the size. – Gyan Nov 13 '19 at 5:33

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