Mencoder error - merging two video files with same fps, resolution and codec failed

Question

Mencoder error in linux - merging two video files with same fps, resolution and video and audio codec failed.

These video files had different fps ratios, video codecs, and Audio codecs but same resolution. I made them to have the same codec by using the below ffmpeg command line per video:

ffmpeg -i D1_vid.mp4 -c:v libx264 -refs 3 -x264-params b-pyramid=2   -acodec aac -b:a 327680  D1_video.mp4

However, even i made them to have many other aspects the same ones (e.g. ref frames) according to MediaInfo, they failed to merged under Mencoder:

` mencoder -oac pcm -ovc copy -o video_out.avi D1_video.mp4 D2_video.mp4

It is the different overall bit rate? How I fix that maintaining all other aspects that are presented by MediaInfo in Linux equal?

output by Mencoder

MEncoder 1.3.0 (Debian), built with gcc-7 (C) 2000-2016 MPlayer Team
success: format: 0  data: 0x0 - 0x2be37eba
libavformat version 57.83.100 (external)
libavformat file format detected.
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7f70ecf872a0]Protocol name not provided, cannot determine if input is local or a network protocol, buffers and access patterns cannot be configured optimally without knowing the protocol
[lavf] stream 0: video (h264), -vid 0
[lavf] stream 1: audio (aac), -aid 0, -alang und
VIDEO:  [H264]  1280x720  24bpp  29.583 fps  4278.2 kbps (522.2 kbyte/s)
[V] filefmt:44  fourcc:0x34363248  size:1280x720  fps:29.583  ftime:=0.0338
==========================================================================
Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
libavcodec version 57.107.100 (external)
AUDIO: 48000 Hz, 1 ch, floatle, 239.1 kbit/15.57% (ratio: 29890->192000)
Selected audio codec: [ffaac] afm: ffmpeg (FFmpeg AAC (MPEG-2/MPEG-4 Audio))
==========================================================================
videocodec: framecopy (1280x720 24bpp fourcc=34363248)
Writing header...
ODML: Aspect information not (yet?) available or unspecified, not writing vprp header.
Writing header...
ODML: Aspect information not (yet?) available or unspecified, not writing vprp header.
Pos:1301.6s  38506f (99%) 1492.89fps Trem:   0min 784mb  A-V:0.020 [4278:767]
success: format: 0  data: 0x0 - 0x208dfde4
libavformat file format detected.
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7f70ecf872a0]Protocol name not provided, cannot determine if input is local or a network protocol, buffers and access patterns cannot be configured optimally without knowing the protocol
[lavf] stream 0: video (h264), -vid 0
[lavf] stream 1: audio (aac), -aid 0, -alang eng
VIDEO:  [H264]  1280x720  24bpp  29.583 fps  3085.4 kbps (376.6 kbyte/s)
[V] filefmt:44  fourcc:0x34363248  size:1280x720  fps:29.583  ftime:=0.0338
==========================================================================
Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
AUDIO: 48000 Hz, 1 ch, floatle, 220.0 kbit/14.32% (ratio: 27498->192000)
Selected audio codec: [ffaac] afm: ffmpeg (FFmpeg AAC (MPEG-2/MPEG-4 Audio))
==========================================================================
videocodec: framecopy (1280x720 24bpp fourcc=34363248)
videocodec: framecopy (1280x720 24bpp fourcc=34363248)

All video files must have identical fps, resolution, and codec for -ovc copy.