输出文件具有双倍持续时间：
源视频时长：00：01：58.88
输出视频时长：00：03：57.76
（视频的持续时间是双倍，音频的持续时间是正确的。所以，视频看起来像是播放了两次，下半场没有声音）
这是日志：
./ ffmpeg -i /Volumes/LANKEXIN/1383.mp4 out.mp4
ffmpeg版本N-82977-g8fd3e02-tessus版权所有（c）2000-2016 FFmpeg开发人员
使用Apple LLVM 8.0.0版（clang-800.0.42.1）构建
配置： - cc = / usr / bin / clang --prefix = / opt / ffmpeg --extra-version = tessus --enable-avisynth --enable-fontconfig --enable-gpl --enable-libass --enable -libbluray --enable-libfreetype --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopus --enable-libschroedinger --enable- libsnappy --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libx264 - enable-libx265 --enable-libxavs --enable-libxvid --enable-libzmq --enable-version3 --disable -ffplay --disable-indev = qtkit --disable-indev = x11grab_xcb
libavutil 55. 43.100 / 55. 43.100
libavcodec 57. 70.100 / 57. 70.100
libavformat 57. 61.100 / 57. 61.100
libavdevice 57. 2.100 / 57. 2.100
libavfilter 6. 68.100 / 6. 68.100
libswscale 4. 3.101 / 4. 3.101
libswresample 2. 4.100 / 2. 4.100
libpostproc 54. 2.100 / 54. 2.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/Volumes/LANKEXIN/1383.mp4':
Metadata:
major_brand : mp42
minor_version : 0
compatible_brands: mp42isom
creation_time : 2017-10-30T14:58:05.000000Z
encoder : mp4creator 1.6.1d
Duration: 00:01:58.88, start: 0.000000, bitrate: 1918 kb/s
Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 1729 kb/s, 25 fps, 25 tbr, 90k tbn, 50 tbc (default)
Metadata:
creation_time : 2017-10-30T14:58:05.000000Z
encoder : VC Coding
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 189 kb/s (default)
Metadata:
creation_time : 2017-10-30T14:58:05.000000Z
File 'out.mp4' already exists. Overwrite ? [y/N] y
[libx264 @ 0x7fbaca003c00] using SAR=1/1
[libx264 @ 0x7fbaca003c00] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 AVX2 LZCNT BMI2
[libx264 @ 0x7fbaca003c00] profile High, level 3.1
[libx264 @ 0x7fbaca003c00] 264 - core 148 - 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
Output #0, mp4, to 'out.mp4':
Metadata:
major_brand : mp42
minor_version : 0
compatible_brands: mp42isom
encoder : Lavf57.61.100
Stream #0:0(eng): 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:
creation_time : 2017-10-30T14:58:05.000000Z
encoder : Lavc57.70.100 libx264
Side data:
cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Stream #0:1(eng): Audio: aac (LC) ([64][0][0][0] / 0x0040), 48000 Hz, stereo, fltp, 128 kb/s (default)
Metadata:
creation_time : 2017-10-30T14:58:05.000000Z
encoder : Lavc57.70.100 aac
Stream mapping:
Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
Stream #0:1 -> #0:1 (aac (native) -> aac (native))
Press [q] to stop, [?] for help
frame= 46 fps=0.0 q=0.0 size= 0kB time=00:00:00.93 bitrate= 0.0kbits/sframe= 64 fps= 45 q=28.0 size= 137kB time=00:00:01.66 bitrate= 672.2kbits/frame= 85 fps= 44 qframe= 5944 fps= 33 q=-1.0 Lsize= 38746kB time=00:03:57.64 bitrate=1335.7kbits/s speed=1.33x 4kB time=00:00:02.94 bitrate= 818.0kbits/s speed= 1.2x
video:36779kB audio:1846kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.311413%
[libx264 @ 0x7fbaca003c00] frame I:24 Avg QP:19.49 size: 67090
[libx264 @ 0x7fbaca003c00] frame P:1806 Avg QP:21.65 size: 14304
[libx264 @ 0x7fbaca003c00] frame B:4114 Avg QP:25.42 size: 2484
[libx264 @ 0x7fbaca003c00] consecutive B-frames: 2.2% 8.1% 25.5% 64.2%
[libx264 @ 0x7fbaca003c00] mb I I16..4: 20.6% 55.8% 23.6%
[libx264 @ 0x7fbaca003c00] mb P I16..4: 5.2% 9.3% 0.8% P16..4: 36.0% 9.9% 4.2% 0.0% 0.0% skip:34.5%
[libx264 @ 0x7fbaca003c00] mb B I16..4: 0.5% 1.0% 0.0% B16..8: 27.2% 1.8% 0.2% direct: 0.9% skip:68.5% L0:48.6% L1:47.6% BI: 3.8%
[libx264 @ 0x7fbaca003c00] 8x8 transform intra:60.9% inter:78.2%
[libx264 @ 0x7fbaca003c00] coded y,uvDC,uvAC intra: 38.3% 61.5% 12.3% inter: 6.6% 11.3% 0.6%
[libx264 @ 0x7fbaca003c00] i16 v,h,dc,p: 22% 35% 10% 33%
[libx264 @ 0x7fbaca003c00] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 21% 24% 21% 5% 6% 6% 6% 5% 6%
[libx264 @ 0x7fbaca003c00] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 24% 33% 11% 4% 7% 6% 6% 4% 4%
[libx264 @ 0x7fbaca003c00] i8c dc,h,v,p: 43% 30% 20% 7%
[libx264 @ 0x7fbaca003c00] Weighted P-Frames: Y:0.3% UV:0.2%
[libx264 @ 0x7fbaca003c00] ref P L0: 73.5% 9.0% 13.8% 3.7% 0.0%
[libx264 @ 0x7fbaca003c00] ref B L0: 92.4% 6.6% 1.1%
[libx264 @ 0x7fbaca003c00] ref B L1: 97.7% 2.3%
[libx264 @ 0x7fbaca003c00] kb/s:1267.21
[aac @ 0x7fbaca021800] Qavg: 897.576