ffmpeg concat error-unusual video

I have been trying to concatenate two 48 seconds video bits to one using the following command

    ffmpeg -f concat -safe 0 -i C:\moviepy-master\concat.txt -c copy output.mp4

When I played it using Windows media player the first 48 second plays fine but the player closes before playing the second bit .

Then I tried to play it using VLC media player but in the second bit player but the audio and video are not in sync .

Then I also tried giving inputs separately so the following error shows up

            C:\Users\SAMHITA VVNK>ffmpeg -f concat -safe 0 -i C:\moviepy-master\extract1.mp4
             -i C:\moviepy-master\extract2.mp4 -c copy -flags +global_header output.mp4
            ffmpeg version N-86723-g3b3501f Copyright (c) 2000-2017 the FFmpeg developers
              built with gcc 7.1.0 (GCC)
              configuration: --enable-gpl --enable-version3 --enable-cuda --enable-cuvid --e
            nable-d3d11va --enable-dxva2 --enable-libmfx --enable-nvenc --enable-avisynth --
            enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv
            --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-li
            bfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug -
            -enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enabl
            e-libopenh264 --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-li
            bsnappy --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolam
            e --enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx
             --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable
            -libxavs --enable-libxvid --enable-libzimg --enable-lzma --enable-zlib
              libavutil      55. 67.100 / 55. 67.100
              libavcodec     57.100.103 / 57.100.103
              libavformat    57. 75.100 / 57. 75.100
              libavdevice    57.  7.100 / 57.  7.100
              libavfilter     6. 94.100 /  6. 94.100
              libswscale      4.  7.101 /  4.  7.101
              libswresample   2.  8.100 /  2.  8.100
              libpostproc    54.  6.100 / 54.  6.100
            C:\moviepy-master\extract1.mp4: Invalid data found when processing input

These are the input file's specifications are as follows C:\Users\SAMHITA VVNK>ffmpeg -i C:\moviepy-master\extract.mp4 -filter_complex "[ 0:v]setpts=0.5*PTS[v];[0:a]atempo=2.0" -map "[a]" extract1fast.mp4

    C:\Users\SAMHITA VVNK>ffmpeg -i C:\moviepy-master\extract2.mp4 -i C:\moviepy-mas
    ter\extract1.mp4
    ffmpeg version N-86723-g3b3501f Copyright (c) 2000-2017 the FFmpeg developers
      built with gcc 7.1.0 (GCC)
      configuration: --enable-gpl --enable-version3 --enable-cuda --enable-cuvid --e
    nable-d3d11va --enable-dxva2 --enable-libmfx --enable-nvenc --enable-avisynth --
    enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv
    --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-li
    bfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug -
    -enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enabl
    e-libopenh264 --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-li
    bsnappy --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolam
    e --enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx
     --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable
    -libxavs --enable-libxvid --enable-libzimg --enable-lzma --enable-zlib
      libavutil      55. 67.100 / 55. 67.100
      libavcodec     57.100.103 / 57.100.103
      libavformat    57. 75.100 / 57. 75.100
      libavdevice    57.  7.100 / 57.  7.100
      libavfilter     6. 94.100 /  6. 94.100
      libswscale      4.  7.101 /  4.  7.101
      libswresample   2.  8.100 /  2.  8.100
      libpostproc    54.  6.100 / 54.  6.100
    Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'C:\moviepy-master\extract2.mp4':
      Metadata:
        major_brand     : isom
        minor_version   : 512
        compatible_brands: isomiso2avc1mp41
        encoder         : Lavf57.56.101
      Duration: 00:00:49.00, start: 0.012993, bitrate: 785 kb/s
        Stream #0:0(eng): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yu
    v420p(tv, smpte170m/smpte170m/bt709), 640x360, 668 kb/s, 29.97 fps, 29.97 tbr, 1
    1988 tbn, 23976 tbc (default)
        Metadata:
          handler_name    : VideoHandler
        Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp,
     137 kb/s (default)
        Metadata:
          handler_name    : SoundHandler
    Input #1, mov,mp4,m4a,3gp,3g2,mj2, from 'C:\moviepy-master\extract1.mp4':
      Metadata:
        major_brand     : isom
        minor_version   : 512
        compatible_brands: isomiso2avc1mp41
        encoder         : Lavf57.56.101
      Duration: 00:00:49.00, start: 0.012993, bitrate: 526 kb/s
        Stream #1:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360 [
    SAR 1:1 DAR 16:9], 462 kb/s, 24.86 fps, 24.86 tbr, 19888 tbn, 49.72 tbc (default
    )
        Metadata:
          handler_name    : VideoHandler
        Stream #1:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, flt
    p, 95 kb/s (default)
        Metadata:
          handler_name    : SoundHandler

Your inputs vary in frame rate, H.264 profile, and audio channels, but the concat demuxer requires that everything be the same. Conform everything to similar parameters before using the concat demuxer, or use the concat filter instead.

Basic example:

ffmpeg -i input0.mp4 -i input1.mp4 -filter_complex "[0:v][0:a][1:v][1:a]concat=n=2:v=1:a=1" output.mp4

This will rely on the defaults of the concat filter which will automatically choose a common pixel format for video streams, and a common sample format, sample rate and channel layout for audio streams. These "common" parameters will, of course, vary depending on your inputs, so it may be advisable to prefix the concat filter with other filters to conform everything if you want consistent results.

Advanced example:

ffmpeg -i input0.mp4 -i input1.mp4 -filter_complex "[0:v]fps=25,format=yuv420p,setpts=PTS-STARTPTS[v0];[0:a]aformat=sample_rates=44100:channel_layouts=stereo,asetpts=PTS-STARTPTS[a0];[1:v]fps=25,format=yuv420p,setpts=PTS-STARTPTS[v1];[1:a]aformat=sample_rates=44100:channel_layouts=stereo,asetpts=PTS-STARTPTS[a1];[v0][a0][v1][a1]concat=n=2:v=1:a=1" -movflags +faststart output.mp4