[FFmpeg-user] Wrong concat video

[Max Grigoriev]

Hi,

I have two video which should be merged together.

Video #1 info

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from
'single_params_file____Users_max.grigoriev_webamg_video-editor_src_test_resources_om.png.mp4':

  Metadata:

    major_brand     : isom

    minor_version   : 512

    compatible_brands: isomiso2avc1mp41

    encoder         : Lavf55.33.100

  Duration: 00:00:10.08, start: 0.033333, bitrate: 164 kb/s

    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p,
1920x1080 [SAR 1:1 DAR 16:9], 4300 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc
(default)

    Metadata:

      handler_name    : VideoHandler

    Stream #0:1(und): Audio: aac (mp4a / 0x6134706D), 48000 Hz, mono, fltp,
128 kb/s (default)

    Metadata:

      handler_name    : SoundHandler

Video #2 info

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from
'single_params_file____Users_max.grigoriev_webamg_video-editor_src_test_resources_a5732-480x320-clip01-sound.mp4':

  Metadata:

    major_brand     : isom

    minor_version   : 512

    compatible_brands: isomiso2avc1mp41

    encoder         : Lavf55.33.100

  Duration: 00:00:15.15, start: 0.050000, bitrate: 2561 kb/s

    Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p,
1920x1080 [SAR 1:1 DAR 16:9], 2444 kb/s, 29.97 fps, 29.97 tbr, 30k tbn,
59.94 tbc (default)

    Metadata:

      handler_name    : VideoHandler

    Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 32000 Hz, stereo,
fltp, 128 kb/s (default)

    Metadata:

      handler_name    : SoundHandler

When I run
"ffmpeg -i video1.mp4  -i video2.mp4 -filter_complex '[0:0] [0:1] [1:0]
[1:1] concat=n=2:v=1:a=1 [v] [a]' -map '[v]' -map '[a]'  output.mp4"

Then I have wrong output. video1 is shown for a moment less than a second
and then remaining time of video1 there's first frame from video2 then
video2 is played as expected. If I change merge order and make video2 +
video1 then everything is OK.

What can be root of problem?
Thanks.