我尝试在基础视频上叠加多个视频，视频被叠加了，但主要基础视频的音频丢失了。另外，如果我想添加更多视频，需要采取什么步骤？
以下是我的命令：
ffmpeg -i master_video.mp4 -i comment_1_offset.mp4 -i comment_2_offset.mp4 -filter_complex "[0:v][1:v]overlay=900:450:enable='between(t\,06,12)'[bg];[bg][2:v]overlay=0:0:enable='between(t\,8,15)'[v]; [1:a][2:a]amerge=inputs=2[a]" -map "[v]" -map "[a]" -ac 2 final_comments.mp4
OUTPUT:
ffmpeg version 3.1 Copyright (c) 2000-2016 the FFmpeg developers
built with Apple LLVM version 7.3.0 (clang-703.0.31)
configuration: --prefix=/usr/local/Cellar/ffmpeg/3.1 --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-opencl --enable-libx264 --enable-libmp3lame --enable-libxvid --disable-lzma --enable-vda
libavutil 55. 27.100 / 55. 27.100
libavcodec 57. 48.101 / 57. 48.101
libavformat 57. 40.101 / 57. 40.101
libavdevice 57. 0.101 / 57. 0.101
libavfilter 6. 46.102 / 6. 46.102
libavresample 3. 0. 0 / 3. 0. 0
libswscale 4. 1.100 / 4. 1.100
libswresample 2. 1.100 / 2. 1.100
libpostproc 54. 0.100 / 54. 0.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'master_video.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
creation_time : 1970-01-01 00:00:00
encoder : Lavf53.24.2
Duration: 00:00:29.57, start: 0.000000, bitrate: 1421 kb/s
Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 1032 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
Metadata:
creation_time : 1970-01-01 00:00:00
handler_name : VideoHandler
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, 5.1, fltp, 383 kb/s (default)
Metadata:
creation_time : 1970-01-01 00:00:00
handler_name : SoundHandler
Input #1, mov,mp4,m4a,3gp,3g2,mj2, from 'comment_1_offset.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf57.40.101
Duration: 00:00:11.28, start: 0.000000, bitrate: 292 kb/s
Stream #1:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 320x240 [SAR 4:3 DAR 16:9], 127 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
Metadata:
handler_name : VideoHandler
Stream #1:1(und): Audio: aac (mp4a / 0x6134706D), 48000 Hz, 5.1, fltp, 338 kb/s (default)
Metadata:
handler_name : SoundHandler
Input #2, mov,mp4,m4a,3gp,3g2,mj2, from 'comment_2_offset.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf57.40.101
Duration: 00:00:15.03, start: 0.000000, bitrate: 409 kb/s
Stream #2:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 320x568, 359 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
Metadata:
handler_name : VideoHandler
Stream #2:1(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 70 kb/s (default)
Metadata:
handler_name : SoundHandler
File 'final_comments.mp4' already exists. Overwrite ? [y/N] y
[Parsed_amerge_2 @ 0x7fc833703300] No channel layout for input 1
[Parsed_amerge_2 @ 0x7fc833703300] Input channel layouts overlap: output layout will be determined by the number of distinct input channels
[libx264 @ 0x7fc833831e00] using SAR=1/1
[libx264 @ 0x7fc833831e00] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 AVX2 LZCNT BMI2
[libx264 @ 0x7fc833831e00] profile High, level 3.1
[libx264 @ 0x7fc833831e00] 264 - core 148 r2668 fd2c324 - H.264/MPEG-4 AVC codec - Copyleft 2003-2016 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=6 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
[mp4 @ 0x7fc833830c00] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead.
Last message repeated 1 times
Output #0, mp4, to 'final_comments.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf57.40.101
Stream #0:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], q=-1--1, 25 fps, 12800 tbn, 25 tbc (default)
Metadata:
encoder : Lavc57.48.101 libx264
Side data:
cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Stream #0:1: Audio: aac (LC) ([64][0][0][0] / 0x0040), 48000 Hz, stereo, fltp, 128 kb/s (default)
Metadata:
encoder : Lavc57.48.101 aac
Stream mapping:
Stream #0:0 (h264) -> overlay:main
Stream #1:0 (h264) -> overlay:overlay
Stream #1:1 (aac) -> amerge:in0
Stream #2:0 (h264) -> overlay:overlay
Stream #2:1 (aac) -> amerge:in1
overlay -> Stream #0:0 (libx264)
amerge -> Stream #0:1 (aac)
Press [q] to stop, [?] for help
[Parsed_overlay_0 @ 0x7fc833702200] [framesync @ 0x7fc8337024e8] Buffer queue overflow, dropping.
Last message repeated 80 times
[Parsed_overlay_1 @ 0x7fc833702be0] [framesync @ 0x7fc833702cc8] Buffer queue overflow, dropping.
Last message repeated 110 times
frame= 44 fps=0.0 q=0.0 size= 0kB time=00:00:00.00 bitrate=N/A speed= frame= 56 fps= 52 q=28.0 size= 0kB time=00:00:00.12 bitrate= 3.2kbits/frame= 69 fps= 43 q=28.0 size= Error while decoding stream #2:1: Cannot allocate memory.26 bitrate=1445.6kbits/s speed=1.35x 00:01.16 bitrate= 0.3kbits/s speed=0.542x
Last message repeated 10 times
Error while decoding stream #2:1: Cannot allocate memory.26 bitrate=1536.6kbits/s speed=1.27x
Last message repeated 37 times
Error while decoding stream #2:1: Cannot allocate memory.68 bitrate=1531.0kbits/s speed=1.24x
Last message repeated 39 times
Error while decoding stream #2:1: Cannot allocate memory.60 bitrate=1419.2kbits/s speed=1.27x
Last message repeated 9 times
frame= 739 fps= 37 q=-1.0 Lsize= 4778kB time=00:00:29.44 bitrate=1329.4kbits/s speed=1.49x
video:4682kB audio:85kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.223951%
[libx264 @ 0x7fc833831e00] frame I:7 Avg QP:16.70 size: 97405
[libx264 @ 0x7fc833831e00] frame P:379 Avg QP:22.09 size: 8715
[libx264 @ 0x7fc833831e00] frame B:353 Avg QP:25.96 size: 2291
[libx264 @ 0x7fc833831e00] consecutive B-frames: 34.9% 1.1% 9.3% 54.7%
[libx264 @ 0x7fc833831e00] mb I I16..4: 14.9% 38.0% 47.1%
[libx264 @ 0x7fc833831e00] mb P I16..4: 2.4% 3.4% 0.5% P16..4: 32.4% 7.8% 3.0% 0.0% 0.0% skip:50.5%
[libx264 @ 0x7fc833831e00] mb B I16..4: 0.2% 0.3% 0.0% B16..8: 28.4% 1.6% 0.2% direct: 0.6% skip:68.5% L0:52.1% L1:45.1% BI: 2.9%
[libx264 @ 0x7fc833831e00] 8x8 transform intra:51.1% inter:69.4%
[libx264 @ 0x7fc833831e00] coded y,uvDC,uvAC intra: 47.1% 69.1% 21.1% inter: 7.0% 11.1% 0.3%
[libx264 @ 0x7fc833831e00] i16 v,h,dc,p: 26% 30% 13% 31%
[libx264 @ 0x7fc833831e00] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 24% 22% 22% 4% 5% 5% 5% 6% 6%
[libx264 @ 0x7fc833831e00] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 22% 17% 11% 8% 9% 9% 8% 9% 8%
[libx264 @ 0x7fc833831e00] i8c dc,h,v,p: 48% 21% 23% 9%
[libx264 @ 0x7fc833831e00] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 0x7fc833831e00] ref P L0: 80.1% 9.7% 8.2% 2.1%
[libx264 @ 0x7fc833831e00] ref B L0: 93.6% 5.5% 0.9%
[libx264 @ 0x7fc833831e00] ref B L1: 96.6% 3.4%
[libx264 @ 0x7fc833831e00] kb/s:1297.28
[aac @ 0x7fc833851c00] Qavg: 805.732