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• ffmpeg why isn't metadata being printed

  13 mars 2020, par akc42

  I would like to capture real time meta data related to the volume of my audio stream when encoding it into a flac file. Ultimately I want to embed all this is a nodejs based web application. I asked a question a while back using the showvolume filter and got all that working with streaming video, running ffmpeg as a subprocess. I want to repeat this with a text based output such as I believe you can get with the -astats filter.

  Here is the command I tried :-

  ffmpeg -hide_banner -nostats -f alsa -acodec pcm_s16le -ac:0 2 -ar 480000 -i hw:CARD=Microphone -af astats=metadata=1:length=1:reset=1 -af ametadata=mode=print:key=lavfi.astats.Overall.Peak_level_dB:file=- -acodec flac test.flac 2>log.txt

  I expected to see stats on the standard output, but saw nothing. The flac file was fine and the log file didn’t show any problems.

  I thought I understood how astats worked ; as configured it should add metadata to the audio stream of 1 second samples of the audio. The second watches the metadata in the stream and when the Peak Level dB is seen it should output it to the file called standard output.

  Obviously I have misunderstood something and haven’t really found any examples to check against. Can someone help

• How to remove silence from an audio file while leaving a bit of the otherwise deleted portion ?

  26 février 2020, par A Question Asker

  Pardon the title, it’s a bit difficult to explain concisely !

  I have a bunch of short (1s-4s) recordings of people reading sentences. They were recorded themselves. Often, there is a bit of silence at the beginning or end, and I would like to automate removing that.

  As a first pass, I used this command :

  sox original.mp3 edited.mp3 silence 1 0.1 2% reverse silence 1 0.1 2% reverse

  The problem is that when people speak, sometimes the very beginning of their speech is quiet and quickly ramps up. This command thus clipped the very beginning of a number of sentences.

  So what I would like to do is essentially the same as what the sox command does, but ideally once it detects the boundary, it leaves 50ms before the boundary, in recognition that there may be some quiet but important sounds.

  I think that ffmpeg might be a good tool for this, as I don’t think sox can be configured like that. I’m tool agnostic. I don’t know ffmpeg at all though, so I appreciate any help putting together a command given ffmpeg’s rather arcane syntax !

  Another nice to have over the aforementioned sox command is for it only to remove silence at the beginning and end (if it exists) — not from the middle of the recording.

  UPDATE : based on time spent with ffmpeg, it looks like I want something like this

  ffmpeg -i input.mp3 -af "silenceremove=start_periods=1:start_threshold=0.02:start_silence=0.1:detection=peak,areverse,silenceremove=start_periods=1:start_threshold=0.02:start_silence=0.1:detection=peak,areverse" output.mp3

  Oddly, this comes out garbled. I thought that it wasn’t reversing properly, but when I try to do something like

  ffmpeg -i input.mp3 -af areverse output.mp3

  It doesn’t work — I just get the input back. I’m not sure what is going wrong ?

  If I just do the beginning,

  ffmpeg -i input.mp3 -af "silenceremove=start_periods=1:start_threshold=0.02:start_silence=0.1:detection=peak" output.mp3

  It works fine — for the beginning. But not sure why the reverse trick is resulting in a garbled output.

  UPDATE2 : it actually looks like the command works, but it changes the metadata in a way that makes itunes wonky. If I use VLC instead, it works fine.

• how to create a radio or video "station" continuous TS stream with ffmpeg

  25 février 2020, par Zibri

  I can’t find any answer to this scenarios :

  Produce a continuous ts file that initially contains silence (or blank video), and as I add files to a text file I wish them to be queued in the output ts stream.
  Think of it as a radio or tv station.
  I found everything on how to stream anything to anything,
  but not a tv/radio broadcast like stream.

  A good start seems to be this :

  ffmpeg -re -y -nostats -nostdin -hide_banner -loglevel quiet -fflags +genpts -f concat -i list.txt -map 0:a? -map 0:v? -map 0:s? -strict -2 -dn -c copy -hls_flags delete_segments -hls_time 10 -hls_list_size 6 /var/www/html/showname_.m3u8

  list.txt example

  file '/mnt/vusolo-tv/show/Season 1/S01E01.mp4'
  
  file '/mnt/vusolo-tv/show/Season 1/S01E02.mp4'

  But i think there can be better ways...

  This is not a good answer either : From multiple video files to single output
  because "All files must have streams with identical encoding. Timebase for streams should be the same. Duration of all streams within a file should be the same, in order to maintain sync."
  And I want to be able to add arbitrary files and produce a TS stream playable by any TV (once broadcasted in dvb).