Hi everyone, I am attempting to leverage ffmpeg in a project that involves recording short audio clips. So far I have gotten some mixed results and I'd like to tap into your collective knowledge to ensure my approach is sound.
Context: - a person records an audio clip of themselves pronouncing a word (imagine that you read aloud a flash-card that says "tree" or "helicopter") - the recording is usually made on a mobile phone The clip contains some silence at both ends, because there is a delay between the moment the user presses the record button, the moment they pronounce their word, and the moment they press "stop". Depending on the device, there may also be an audible click in the beginning. My objective is to trim the silence at both ends and apply fade-in/out to soften the clicks, if any. The challenges are: - ffmpeg's silenceremove filter needs a threshold value, however, - each user is in their own environment, with different levels of ambient noise - each device is unique in terms of sensitivity Thus, I can achieve my desired result with one specific clip through trial and error, tinkering with thresholds until I get what I need. But I cannot figure out how to detect these thresholds automatically, such that I can replicate the result with a broad range of users, environments and recording devices. Note that there is no expectation to produce perfect results that match the quality of an audio recording studio, I'm more in the "rough, but good enough for practical purposes" territory. Having read the documentation and various forums, I put together this pipeline (actual commands in the appendix): 1. run volumedetect to see what the maximum level is 1a. parse stdout to extract `max_volume` 2. normalize audio to `max_volume` 3. apply silenceremove with <empirically determined threshold> 3a. for the beginning of the file 3b. invert the stream and run another silenceremove for the beginning (which is actually the end) 3c. invert it back and save the output What I read in the forums gave me the impression that we need step#2 such that at step#3 we could say the threshold is 0. However, that is not the case, I still had to find a reasonable threshold via trial and error. After I found a value that produces a good result, I assumed that it might be good enough for practical purposes and it would be OK to simply hardcode it into my code as a magic number. However, on the next day I attempted to replicate the results using the same recording device in the same room - but this time ffmpeg would tell me the filtered stream is empty, nothing to write. The environment wasn't 100% identical, since I'm not doing this in a controlled lab, but most of the variables are the same, though perhaps the windows were open and it was a different time of the day, so the baseline noise level outside was somewhat different. Clearly, my approach is not robust. I'd like to understand whether there are any low-hanging fruits that I can try, or if I'm not on the right track. I imagine that the solution I need would somehow determine the silence threshold relative to the rest of the file, instead of using a "one fits all" value. However I did not find such filters or analyzers in ffmpeg. Your guidance will be greatly appreciated, Alex Appendix, pipeline commands 1. ffmpeg -i input.mp3 -af "volumedetect" -f null /dev/null here I parse stdout, looking for something like "[Parsed_volumedetect_0 @ 0x559dbe815f00] max_volume: -15.9 dB" 2. ffmpeg -i input.mp3 -af "volume=15.9dB" out2-normalized.mp3 3. ffmpeg -i out2-normalized.mp3 -af silenceremove=start_periods=1:start_duration=0:start_threshold=-6dB:start_silence=0.5,areverse,silenceremove=start_periods=1:start_duration=0:start_threshold=-6dB:start_silence=0.5,afade=t=in:st=0:d=0.3,areverse,afade=t=in:st=0:d=0.3 out3-trimmed.mp3 An example of an input file is available at railean.net/files/public-temp/in-fresh.mp3, after normalization you can hear some church bells in the distance. I'm totally fine with them remaining audible in the result, as long as the leading and trailing silence is removed. _______________________________________________ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".