[FFmpeg-user] Howto sync two audio streams and mix them

[Denis Mysenko]

 You cannot use 'itsoffset' to delay an audio stream, you need 'adelay' audiofilter instead.

Eg. [1:0]adelay=10|10[out1] to produce a 10 second delayed audio from stream 1:0 and call it out1

So your case could be:
ffmpeg -y -i 20150416203941.broadcast.ts -i 
20150416203941.broadcast.ts -filter_complex "[0:1]adelay=10|10[track1];[track1][1:2]amix[mixout]" -c:v 
copy -c:a aac -b:a 128k -ar 44100 -strict -2 -map 0:0 -map [mixout] -f flv test1.flv

Note that 10 second delay is specified twice – separately for left and right channels

Суббота, 18 апреля 2015, 9:38 +02:00 от Thomas Seilund <tps at netmaster.dk>:
>Hi all
>
>I have an mpegts container with one video and two audio streams.
>
>I what to mix the two audio streams. At the same time the second audio 
>stream must be delayed 10 seconds to match the first audio stream.
>
>Here is what I have as input
>
>tps at t420:~/video/test$ ffprobe -i 20150416203941.broadcast.ts
>ffprobe version N-69238-g2699a37 Copyright (c) 2007-2015 the FFmpeg 
>developers
>   built on Feb 24 2015 18:13:15 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
>   configuration: --enable-gpl --enable-libmp3lame --enable-libvpx --enable- 
>libx264 --enable-version3 --enable-libvorbis --enable-libfreetype --enable- 
>libv4l2 --enable-libfdk-aac --enable-nonfree --enable-libpulse
>   libavutil      54. 17.100 / 54. 17.100
>   libavcodec     56. 20.100 / 56. 20.100
>   libavformat    56. 19.100 / 56. 19.100
>   libavdevice    56.  4.100 / 56.  4.100
>   libavfilter     5.  8.101 /  5.  8.101
>   libswscale      3.  1.101 /  3.  1.101
>   libswresample   1.  1.100 /  1.  1.100
>   libpostproc    53.  3.100 / 53.  3.100
>Input #0, mpegts, from '20150416203941.broadcast.ts':
>   Duration: 00:00:18.69, start: 1.400000, bitrate: 4186 kb/s
>   Program 1
>     Metadata:
>       service_name    : Service01
>       service_provider: FFmpeg
>     Stream #0:0[0x100]: Video: h264 (Constrained Baseline) ([27][0][0][0] / 
>0x001B), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 25 fps, 25 tbr, 90k tbn, 50 
>tbc
>     Stream #0:1[0x101]: Audio: mp2 ([3][0][0][0] / 0x0003), 48000 Hz, 
>stereo, s16p, 384 kb/s
>     Stream #0:2[0x102]: Audio: mp2 ([3][0][0][0] / 0x0003), 48000 Hz, 
>stereo, s16p, 384 kb/s
>tps at t420:~/video/test$
>
>
>
>Here is what I do
>
>ffmpeg -y -i 20150416203941.broadcast.ts -itsoffset 10 -i 
>20150416203941.broadcast.ts -filter_complex "[0:1][1:2]amix[mixout]" -c:v 
>copy -c:a aac -b:a 128k -ar 44100 -strict -2 -map 0:0 -map [mixout] -f flv 
>test1.flv
>
>
>
>The two audio streams are mixed ok but the timestamps of the second audio 
>stream are not shifted 10 seconds.
>
>
>
>Actually, the following command without the -itsoffset 10 parameter 
>produces the same output
>
>ffmpeg -y -i 20150416203941.broadcast.ts -i 20150416203941.broadcast.ts - 
>filter_complex "[0:1][1:2]amix[mixout]" -c:v copy -c:a aac -b:a 128k -ar 
>44100 -strict -2 -map 0:0 -map [mixout] -f flv test2.flv
>
>
>
>What am I doing wrong?
>
>Any help would be appreciated.
>
>Thanks
>
>Thomas S
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Sincerely,
-- 
Denis Mysenko, CCNA, MCP, MCSA
Skype: denismysenko, ICQ: 555955 
Forskarbacken 9 / 209
10405 Stockholm, Sweden

Mobile: +46 (0) 70 405 49 04