我用这个命令连接六个 m4a 文件
ffmpeg -f concat -i audiofiles.txt -c copy all_audio_edited.m4a
每个文件的时长为 4 小时（总共 24 小时），但连接效果不太好：文件的第一部分（第一个 m4a）是完美的，但其他部分都变慢了，所以最终的时长>26 小时
怎么了？
谢谢
Marcs-MacBook-Pro:Sof marc$ ffmpeg -report -f concat -i audiofiles.txt -c copy all_audio_edited.m4a
ffmpeg started on 2014-08-28 at 23:35:06
Report written to "ffmpeg-20140828-233506.log"
ffmpeg version 2.3 Copyright (c) 2000-2014 the FFmpeg developers
built on Aug 26 2014 17:59:15 with Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
configuration: --prefix=/usr/local/Cellar/ffmpeg/2.3 --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-nonfree --enable-hardcoded-tables --enable-avresample --enable-vda --cc=clang --host-cflags= --host-ldflags= --enable-libx264 --enable-libfaac --enable-libmp3lame --enable-libxvid --enable-libfreetype --enable-libtheora --enable-libvorbis --enable-libvpx --enable-librtmp --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libvo-aacenc --enable-libass --enable-ffplay --enable-libspeex --enable-libschroedinger --enable-libfdk-aac --enable-openssl --enable-libopus --enable-frei0r --enable-libcaca --enable-libquvi --enable-libvidstab --enable-libx265 --enable-libopenjpeg --extra-cflags='-I/usr/local/Cellar/openjpeg/1.5.1_1/include/openjpeg-1.5 '
libavutil 52. 92.100 / 52. 92.100
libavcodec 55. 69.100 / 55. 69.100
libavformat 55. 48.100 / 55. 48.100
libavdevice 55. 13.102 / 55. 13.102
libavfilter 4. 11.100 / 4. 11.100
libavresample 1. 3. 0 / 1. 3. 0
libswscale 2. 6.100 / 2. 6.100
libswresample 0. 19.100 / 0. 19.100
libpostproc 52. 3.100 / 52. 3.100
[concat @ 0x7fcb6c803400] Estimating duration from bitrate, this may be inaccurate
Input #0, concat, from 'audiofiles.txt':
Duration: 00:00:00.00, start: 0.000000, bitrate: 279 kb/s
Stream #0:0: Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 280 kb/s
Output #0, ipod, to 'all_audio_edited.m4a':
Metadata:
encoder : Lavf55.48.100
Stream #0:0: Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, 280 kb/s
Stream mapping:
Stream #0:0 -> #0:0 (copy)
Press [q] to stop, [?] for help
size= 3020597kB time=26:07:14.44 bitrate= 263.1kbits/s
video:0kB audio:3004946kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.520849%