[FFmpeg-user] duration problem of concatenated audio in powerpoint

[yiminhe at gmail.com]

Hi all,

I'm using ffmpeg to concatenate some mp3 audios. 
There is no problem when playing the concatenated audio with VLC and WMP. 
But if I inserted them into PPT files with Microsoft PowerPoint, the duration displayed in powerpoint is smaller than actual duration. And the player stopped very early (at position ~70%) if I playing them in fullscreen mode in powerpoint. 

Here is the minimal example code: 

[root at localhost audio-concatenate]# ll 
total 24 
-rw-r--r-- 1 root root 19688 Nov 24 11:19 a.mp3 
drwxr-xr-x 3 root root 4096 Nov 18 11:37 mp3 

[root at localhost audio-concatenate]# ffmpeg -i a.mp3 -i a.mp3 -filter_complex "concat=n=2:v=0:a=1" two_a.mp3 
ffmpeg version 2.4.3- http://johnvansickle.com/ffmpeg/ Copyright (c) 2000-2014 the FFmpeg developers 
built on Nov 4 2014 13:14:24 with gcc 4.8 (Debian 4.8.3-13) 
configuration: --enable-gpl --enable-version3 --disable-shared --disable-debug --enable-runtime-cpudetect --enable-libmp3lame --enable-libx264 --enable-libx265 --enable-libwebp --enable-libspeex --enable-libvorbis --enable-libvpx --enable-libfreetype --enable-fontconfig --enable-libxvid --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libtheora --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-gray --enable-libopenjpeg --enable-libopus --disable-ffserver --enable-libass --enable-gnutls --cc=gcc-4.8 
libavutil 54. 7.100 / 54. 7.100 
libavcodec 56. 1.100 / 56. 1.100 
libavformat 56. 4.101 / 56. 4.101 
libavdevice 56. 0.100 / 56. 0.100 
libavfilter 5. 1.100 / 5. 1.100 
libswscale 3. 0.100 / 3. 0.100 
libswresample 1. 1.100 / 1. 1.100 
libpostproc 53. 0.100 / 53. 0.100 
[mp3 @ 0x27d45c0] Estimating duration from bitrate, this may be inaccurate 
Input #0, mp3, from 'a.mp3': 
Metadata: 
encoder : Lavf56.4.101 
Duration: 00:00:04.91, start: 0.000000, bitrate: 32 kb/s 
Stream #0:0: Audio: mp3, 22050 Hz, mono, s16p, 32 kb/s 
[mp3 @ 0x27e4d40] Estimating duration from bitrate, this may be inaccurate 
Input #1, mp3, from 'a.mp3': 
Metadata: 
encoder : Lavf56.4.101 
Duration: 00:00:04.91, start: 0.000000, bitrate: 32 kb/s 
Stream #1:0: Audio: mp3, 22050 Hz, mono, s16p, 32 kb/s 
Output #0, mp3, to 'two_a.mp3': 
Metadata: 
TSSE : Lavf56.4.101 
Stream #0:0: Audio: mp3 (libmp3lame), 22050 Hz, mono, s16p (default) 
Metadata: 
encoder : Lavc56.1.100 libmp3lame 
Stream mapping: 
Stream #0:0 (mp3) -> concat:in0:a0 
Stream #1:0 (mp3) -> concat:in1:a0 
concat -> Stream #0:0 (libmp3lame) 
Press [q] to stop, [?] for help 
size= 39kB time=00:00:09.82 bitrate= 32.3kbits/s 
video:0kB audio:39kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.506368% 

How can I fix this?

Thanks!


yiminhe at gmail.com