On Wed, Sep 18, 2019 at 12:07:45 +0000, Kieran O'Leary wrote: > This is the command I used to do a one second test where the > intention is to merge two mono audio tracks into one stereo track - i > was hoping that there was a way to do this without a filter but i > guess not?:
You do need a filter, as you are technically merging two streams into one. There is no other method to do so. > ffmpeg -i "input.mov" -filter_complex " > [0:2][0:3]join=inputs=2:channel_layout=stereo[a]" -map "[a]" -c:a pcm_s24le > -c: > v copy -t 1 output.mov [...] > What is the best way to verify that the process was lossless? > > I tried the following which seems very clumsy: > 1. Export the two original audio tracks as seperate wav files with (i know i > could have done it in one command but I just knocked this together) > ffmpeg -i input.mov -c:a copy -t 1 -map 0:2 left.wav > ffmpeg -i input.mov -c:a copy -t 1 -map 0:3 right.wav That is indeed clumsy. You can check the framemd5 from the original and the result without dumping to intermediate files: (Untested) $ ffmpeg -i input.mov -c:a copy -t 1 -map 0:2 -f framemd5 - $ ffmpeg -i input.mov -c:a copy -t 1 -map 0:3 -f framemd5 - $ ffmpeg -i output.mov -c:a copy -c:a -map_channel 0.0.0 -f framemd5 - $ ffmpeg -i output.mov -c:a copy -c:a -map_channel 0.0.1 -f framemd5 - Actually, the frame* muxers even differentiate between their different output streams anyway, by means of an index, so you can do: $ ffmpeg -i input.mov -c:a copy -t 1 -map 0:2 -map 0:3 -f framemd5 - for the input. (This works with the copy codec because inputs and outputs are pcm_s24le and expected to be identical. Otherwise you would need to force it, or in the case of the framehash/framemd5 muxers, that's their default codec anyway.) I'm not sure on this caveat but: Note that the frame muxers work on audio *packets*, IIUC. If a muxer decides to repacket the audio samples differently, I assume you might get different "frame" hashes. You might want to instead use the hash/md5 muxers, but they will not tell you where the difference lies if something was snipped from the end. Cheers, Moritz _______________________________________________ ffmpeg-user mailing list [email protected] https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email [email protected] with subject "unsubscribe".
