[FFmpeg-user] How to pipe png output from FFmpeg into cavif.

[bat guano]

​Hi
FFmpeg doesn't have ability to create avif image files (yet).
I have used FFmpeg to re-size png files then convert them with cavif program.
(Releases of cavif are here ---> https://github.com/kornelski/cavif-rs/releases)

Like this...
ffmpeg -i infile.png -vf scale="424:-1" temp.png; cavif --output outfile.avif temp.png

$ ffmpeg -i infile.png -vf scale="424:-1" temp.png; cavif --output outfile.avif temp.png
ffmpeg version N-101507-gb2d0826 Copyright (c) 2000-2021 the FFmpeg developers
  built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.12) 20160609
  configuration: --enable-gpl --enable-nonfree --enable-libfdk-aac --enable-libmp3lame --enable-libvorbis --enable-libwebp --enable-libx264
  libavutil      56. 68.100 / 56. 68.100
  libavcodec     58.131.100 / 58.131.100
  libavformat    58. 73.100 / 58. 73.100
  libavdevice    58. 12.100 / 58. 12.100
  libavfilter     7.109.100 /  7.109.100
  libswscale      5.  8.100 /  5.  8.100
  libswresample   3.  8.100 /  3.  8.100
  libpostproc    55.  8.100 / 55.  8.100
Input #0, png_pipe, from 'infile.png':
  Duration: N/A, bitrate: N/A
  Stream #0:0: Video: png, rgba(pc), 800x505 [SAR 2835:2835 DAR 160:101], 25 fps, 25 tbr, 25 tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (png (native) -> png (native))
Press [q] to stop, [?] for help
Output #0, image2, to 'temp.png':
  Metadata:
    encoder         : Lavf58.73.100
  Stream #0:0: Video: png, rgba(pc, progressive), 424x268 [SAR 5360:5353 DAR 160:101], q=2-31, 200 kb/s, 25 fps, 25 tbn
    Metadata:
      encoder         : Lavc58.131.100 png
frame=    1 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.04 bitrate=N/A speed=1.07x
video:65kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
outfile.avif: 17KB (16668B color, 0B alpha, 188B HEIF)

=======================================================================================
But cavif has an option to accept input from stdin.

$ ./cavif --version
cavif-rs 0.6.6

$ ./cavif --help
cavif-rs 0.6.6
Kornel Lesiński <kornel at imageoptim.com>
Convert JPEG/PNG images to AVIF image format (based on AV1/rav1e)

USAGE:
    cavif [OPTIONS] [IMAGES]...

OPTIONS:
    -Q, --quality <n>      Quality from 1 (worst) to 100 (best) [default: 80]
    -s, --speed <n>        Encoding speed from 1 (best) to 10 (fast but ugly)
                           [default: 1]
    -f, --overwrite        Replace files if there's .avif already
    -o, --output <path>    Write output to this path instead of same_file.avif.
                           It may be a file or a directory.
    -q, --quiet            Don't print anything
        --dirty-alpha      Keep RGB data of fully-transparent pixels (makes
                           larger, lower quality files)
        --color <color>    Internal AVIF color space [default: ycbcr]  [possible
                           values: ycbcr, rgb]
    -h, --help             Prints help information
    -V, --version          Prints version information

ARGS:
    <IMAGES>...    One or more JPEG or PNG files to convert. "-" is
                   interpreted as stdin/stdout.
======================================================================================

How do I make FFmpeg send it's png output to stdout?

With a command like this...
ffmpeg -i infile.png -vf scale="424:-1" -; cavif --output outfile.avif -

I think I need to define a format for FFmpeg with "-f whatever"

What format would be needed?


$ ffmpeg -i infile.png -vf scale="424:-1" -; cavif --output outfile.avif -
ffmpeg version N-101507-gb2d0826 Copyright (c) 2000-2021 the FFmpeg developers
  built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.12) 20160609
  configuration: --enable-gpl --enable-nonfree --enable-libfdk-aac --enable-libmp3lame --enable-libvorbis --enable-libwebp --enable-libx264
  libavutil      56. 68.100 / 56. 68.100
  libavcodec     58.131.100 / 58.131.100
  libavformat    58. 73.100 / 58. 73.100
  libavdevice    58. 12.100 / 58. 12.100
  libavfilter     7.109.100 /  7.109.100
  libswscale      5.  8.100 /  5.  8.100
  libswresample   3.  8.100 /  3.  8.100
  libpostproc    55.  8.100 / 55.  8.100
Input #0, png_pipe, from 'infile.png':
  Duration: N/A, bitrate: N/A
  Stream #0:0: Video: png, rgba(pc), 800x505 [SAR 2835:2835 DAR 160:101], 25 fps, 25 tbr, 25 tbn, 25 tbc
[NULL @ 0x3f96480] Unable to find a suitable output format for 'pipe:'
pipe:: Invalid argument

======================================================================================