I want to upload a video stream (from a file) to remote server using ffserver feed. I'm using as simple configuration as possible. So ffserver.conf is defined as following (relevant part):

<Feed feed1.ffm>
        File /tmp/feed1.ffm
        FileMaxSize 100M
        ACL allow
<Stream test1>
        Feed feed1.ffm
        Format mpeg
        VideoCodec libx264
        AudioBitRate 32
        AudioChannels 1
        AudioSampleRate 44100
        VideoBitRate 128
        VideoBitRateRange 128-1024
        VideoBufferSize 40
        VideoFrameRate 25
        VideoSize 640x480
        VideoGopSize 12
        VideoQMin 1
        VideoQMax 15
File I'm trying to upload has following properties:

Input #0, avi, from '01-20180608082004.avi':
encoder : Lavf56.40.101
Duration: 00:06:31.81, start: 0.000000, bitrate: 510 kb/s
Stream #0:0: Video: mpeg4 (Simple Profile) (FMP4 / 0x34504D46), yuv420p, 640x480 [SAR 1:1 DAR 4:3], 505 kb/s, 27 fps, 27 tbr, 27 tbn, 27 tbc
I'm trying to upload by running following command:

ffmpeg -i 01-20180608082004.avi http://localhost:8090/feed1.ffm
During the upload I'm getting a lot of messages like this:

[libx264 @ 0x26078e0] VBV underflow (frame 2359, -93296 bits)
[libx264 @ 0x26078e0] VBV underflow (frame 2361, -132704 bits)
[libx264 @ 0x26078e0] VBV underflow (frame 2362, -11856 bits)
[libx264 @ 0x26078e0] VBV underflow (frame 2363, -6048 bits)
[libx264 @ 0x26078e0] VBV underflow (frame 2364, -4232 bits)
[libx264 @ 0x26078e0] VBV underflow (frame 2365, -14240 bits)
[libx264 @ 0x26078e0] VBV underflow (frame 2366, -53224 bits)
And when I'm trying then to download the file http://localhost:8090/test1 it neither finishes download nor can be played.

I tried to add an ASF stream and download it but it couldn't be played by any player.

Is there some mistake during file upload?