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I am trying to mix a few files with FFMPEG that are mka and are from a Twilio Video Conference recording. I am trying to get tracks for each participant but I am trying to keep the overall timestamp from the file.

Concrete example: i have these three files:

0PA1896e43f4ca0edf17d8dbfc0bab95a52.mka
1PA2a640f11bc13af2c29397800f058cb05.mka
2PA9fa5b32edc016f6f5b9669bb9b308d97.mka

These files are all tracks of a participant in the call but joined at different times(left the meeting and re-entered, results in a new file).

I want to mix those files in a single file while keeping the timestamp when it was recorded. FFProbe shows the start of each of this files:

0PA1896e43f4ca0edf17d8dbfc0bab95a52.mka - Duration: 00:00:17.87, start: 1.360000, bitrate: 78 kb/s
1PA2a640f11bc13af2c29397800f058cb05.mka - Duration: 00:00:22.76, start: 22.521000, bitrate: 78 kb/s
2PA9fa5b32edc016f6f5b9669bb9b308d97.mka - Duration: 00:00:20.36, start: 48.944000, bitrate: 78 kb/s

So the first 00:00:17.87 should be silenced, then append the second file from 00:00:22.76 and the third from 48.944000. This would result a single file with all those 3 recording added but with silence when there is nothing, with all the recordings added. Practically, i want a delay at the start.

Imagine i'm adding a 4th recording that starts at minute 2, between recording 3 and 4 would be a gap of silence.

Or imagine a call with 3 participants but the 3rd one would enter only from minute 5. The first 5 minutes should be silenced so I can pass the trascribe api the 3rd participant and still get the correct timestamps.

The reason i want it this way is because I want to transcribe the audio to text and want the exact timestamp when the text can be heard.

Filip
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1 Answers1

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You would use the aresample and amix filters for this. The aresample filter will be applied to each input in order to insert silence till the starting timestamp. These processed streams are then mixed together with the amix filter.

I'm going call the inputs 0.mka, 1.mka and 2.mka

ffmpeg -copyts -i 0.mka -i 1.mka -i 2.mka -filter_complex "[0]aresample=async=1:first_pts=0[a0];[1]aresample=async=1:first_pts=0[a1];[2]aresample=async=1:first_pts=0[a2];[a0][a1][a2]amix=inputs=3" out.mka
Gyan
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  • Gyan you saved my day!! I changed the filter to keep the timestamp, but add each audio to each channel, may be someone can give a try... : `ffmpeg -hide_banner -stats -progress -copyts -i audio2/RT3d86a5a1c64268c66653b526466ac864.mka -i audio2/RT91ddb2cce8a309b9da7b25fe4d9e3a3b.mka -filter_complex "[0]aresample=async=1:first_pts=0[a0];[1]aresample=async=1:first_pts=0[a1];[a0]amix=inputs=1,pan=mono|c0=c0[ch1];[a1]amix=inputs=1,pan=mono|c0=c0[ch2];[ch1][ch2]amerge=inputs=2,pan=stereo|c0 – jsturnio Aug 03 '22 at 12:36