use FFMpeg to send BMPs to stdout

Question

I see lots of examples using FFMpeg to make a video file from a set of images. I can also see how to do the opposite if I want individual files. However, I want the images to be pushed to stdout. This line fails:

ffmpeg -hwaccel auto -i Wildlife.wmv -pix_fmt bgr24 -an -sn -f bmp - > junk.bin

It says "Requested output format 'bmp' is not a suitable output format". However, this line works fine to generate image files:

ffmpeg -hwaccel auto -i Wildlife.wmv -pix_fmt bgr24 -an -sn test%03d.bmp

How can I get images pushed to stdout?

Solution

The problem is that in ffmpeg, BMP is not a file format. It's an encoder (as seen under ffmpeg -encoders). Normal BMP files can be written with the image2 muxer, but if you only want the raw video codec, you need the rawvideo format.

So, use something like this:

ffmpeg -i input.wmv -c:v bmp -f rawvideo -an - > output.bin

Comments

[Glenn Slayden]

Further discussion of this exact issue here.

[Glenn Slayden]

Followup question to your helpful answer... what's the difference between the image2 and image2pipe muxers in ffmpeg?

[slhck]

@GlennSlayden image2 reads from actual files specified by filename; image2pipe reads from a pipe, that is, images piped via STDIN.

[Glenn Slayden]

Yes, sorry, my question should have been, why are separate binaries needed for that when external piping of stdin and/or stdout should be transparent to any program?

[slhck]

@GlennSlayden Not sure I understand. You don't need separate binaries – just one ffmpeg. image2pipe is a fairly simple demuxer part of the image2 code, whereas image2 needs additional capabilities to deal with filenames.