> I would expect output.m4a to be 25 seconds long: 5 seconds normal playback, > 10 seconds atempo=0.5, 10 seconds normal. Instead it is 15 seconds long and > doesn't contain the last 10 seconds of normal playback.
I have experimented with some alternatives to achieve the same goal. If I do the above process in two stages, first merge the audio tracks, output to an intermediate file, then apply atempo to the intermediate, e.g: $ ffmpeg -y \ -i BigBuckBunny_320x180_t10.mp4 \ -i BigBuckBunny_320x180_t10.mp4 \ -filter_complex " aevalsrc=0:d=10[na1]; [na1][1:a]concat=n=2:v=0:a=1[a1]; [0:a][a1]amix=inputs=2[mix_audio] " \ -map [mix_audio] \ -c:a aac \ intermediate.m4a $ ffmpeg -y \ -i intermediate.m4a \ -filter_complex " [0:a]asplit=3[a0][a1][a2]; [a0]atrim=0:5,asetpts=expr=PTS-STARTPTS[a_trim0]; [a1]atrim=5:10,asetpts=expr=PTS-STARTPTS[a_trim1]; [a2]atrim=10:20,asetpts=expr=PTS-STARTPTS[a_trim2]; [a_trim1]atempo=0.5[a_slomo1]; [a_trim0][a_slomo1][a_trim2]concat=n=3:v=0:a=1[com_a_slomo] " \ -map [com_a_slomo] \ -c:a aac \ output.m4a This works as expected. Also, if I instead do the merge in one stage, but first ensure that both audio tracks are the same length as the final output by appending silent audio to the end of [0:a]: ffmpeg -y \ -i BigBuckBunny_320x180_t10.mp4 \ -i BigBuckBunny_320x180_t10.mp4 \ -filter_complex " aevalsrc=0:d=10[na0];[0:a][na0]concat=n=2:v=0:a=1[a0]; aevalsrc=0:d=10[na1];[na1][1:a]concat=n=2:v=0:a=1[a1]; [a0][a1]amix=inputs=2[mix_audio]; [mix_audio]asplit=3[mix_audio0][mix_audio1][mix_audio2]; [mix_audio0]atrim=0:5,asetpts=expr=PTS-STARTPTS[a_trim0]; [mix_audio1]atrim=5:10,asetpts=expr=PTS-STARTPTS[a_trim1]; [mix_audio2]atrim=10:20,asetpts=expr=PTS-STARTPTS[a_trim2]; [a_trim1]atempo=0.5[a_slomo1]; [a_trim0][a_slomo1][a_trim2]concat=n=3:v=0:a=1[com_a_slomo] " \ -map [com_a_slomo] \ -c:a aac \ output.m4a This works as expected too. Therefore, I wonder if label [mix_audio] in the original command does not have the correct length assigned or something? Saving to an intermediate file enforces that 25 second length, and so does appending silent audio to make both tracks the full length. _______________________________________________ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
