[FFmpeg-user] ffmpeg pipe svg image sequence error

[Michael Lucarz]

With ffmpeg 3.4, you can now render svg image sequences. With the following
it works:

ffmpeg -i images/image-%02d.svg video.mp4

However, piping via

cat images/*.svg | ffmpeg -f image2pipe -c:v svg -i - video.mp4

results in the following error

ffmpeg version N-88409-ga8305b0ea3 Copyright (c) 2000-2017 the FFmpeg developers
  built with Apple LLVM version 9.0.0 (clang-900.0.37)
  configuration: --prefix=./bin --enable-gpl --enable-nonfree
--enable-librsvg --enable-libass --enable-libfdk-aac
--enable-libfreetype --enable-libmp3lame --enable-libtheora
--enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265
--enable-libopus --enable-libxvid
  libavutil      56.  0.100 / 56.  0.100
  libavcodec     58.  1.100 / 58.  1.100
  libavformat    58.  0.102 / 58.  0.102
  libavdevice    58.  0.100 / 58.  0.100
  libavfilter     7.  0.101 /  7.  0.101
  libswscale      5.  0.101 /  5.  0.101
  libswresample   3.  0.100 /  3.  0.100
  libpostproc    55.  0.100 / 55.  0.100
[image2pipe @ 0x7fe0d1800000] Could not find codec parameters for
stream 0 (Video: svg (librsvg), none): unspecified size
Consider increasing the value for the 'analyzeduration' and 'probesize' options
Input #0, image2pipe, from 'pipe:':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Video: svg, none, 25 tbr, 25 tbn, 25 tbc
Output #0, mp4, to 'video.mp4':
Output file #0 does not contain any stream

Digging into img2dec.c I can see it's probing for <?xml on the first line
and <svg on the following line:

static int svg_probe(AVProbeData *p)
{
    const uint8_t *b = p->buf;
    const uint8_t *end = p->buf + p->buf_size;
    if (memcmp(p->buf, "<?xml", 5))
        return 0;
    while (b < end) {
        b += ff_subtitles_next_line(b);
        if (b >= end - 4)
            return 0;
        if (!memcmp(b, "<svg", 4))
            return AVPROBE_SCORE_EXTENSION + 1;
    }
    return 0;
}

All of the svg files in the folder have the appropriate headers

<?xml version="1.0" encoding="utf-8"?>
<svg xmlns="http://www.w3.org/2000/svg" width="640" height="640">

What am I missing?

Lastly, I'm using a compiled version of ffmpeg since installing via brew
install ffmpeg --with-librsvg didn't seem to work. It installed fine,
however it would give the following error

Decoder (codec svg) not found for input stream #0:0

I should note, I've tried setting analyzeduration and probesize options as
well as setting dimensions for input and output with no success.

Any help would be greatly appreciated!

Mike