Does webm/mka/mkv/mp4 support discontinuous audio streams?
I'm wondering, can ffmpeg transcode .wav-audio into opus-encapsulated-into-webm, but filter out silent frames - especially full seconds of silence, completely drop them from the stream to save space? (maybe via https://ffmpeg.org/ffmpeg-bitstream-filters.html ?)
The goal of all this is to very efficiently represent near-silence in phone-call-recording files for archival purposes (i.e. by completely omitting it from the stream and having it replaced by digital zeros at audio decoding time).
As far as I understand opus-encapsulated-into-ogg does not support such timestamp discontinuities. opus-encapsulated-into-rtp assumingly does support this, but I'm wondering if more "offline" formats such as webm and whether it's possible to produce them directly without passing by rtp format first.
These frames could then be replaced by zeros at audio decoding time by some form of PLC or DTS gaps replacement by zero signal.
Thanks!
UPD1: Unfortunately, silenceremove filter does not work as I need it. The way I used it below, the audio duration after silenceremove is shortened by the amount of silence. This is not what I am looking for. I am looking to preserve the timestamps, have the silence imputed by digital silence at decoding time and preserve the original audio duration (as reported by ffprobe or audio players)
ffmpeg -y -f lavfi -i sine=f=440:d=5 -f lavfi -i anullsrc=d=3600:cl=mono -f lavfi -i sine=f=880:d=5 -filter_complex "[0][1][2]concat=n=3:v=0:a=1" 5sec_silent1h_5sec.wav
ffmpeg -y -i 5sec_silent1h_5sec.wav -acodec libopus 5sec_silent1h_5sec.opus
ffmpeg -y -i 5sec_silent1h_5sec.wav -acodec libopus -af silenceremove=window=0:detection=peak:stop_mode=all:start_mode=all:stop_periods=-1:stop_threshold=0 5sec_5sec.mkv
The good duration of 5sec_silent1h_5sec.opus and bad duration of 5sec_5sec.mkv are confirmed by ffprobe (1h10s and 10s respectively).
Is there a way to adjust the filters/command line arguments to preserve the audio duration?
UPD2
The following somewhat works, although ~1s of 880hz audio leaks into the first segment (before the long silence segment), no matter how I adjust the between bounds - very strange!
ffmpeg -y -i 5sec_silent1h_5sec.wav -acodec libopus -af "aselect='between(t,0,4)+between(t,3606,3610)'" 5sec_silent1h_5sec_with_leakage.mkv
If this leakage can be fixed, then this can be used together with silencedetect filter.
But of course it would be nicer to get the output in a single invokation of ffmpeg.
The example output file with "leakage": https://1drv.ms/u/s!Apx8USiTtrYmq9Q4QaETF2OJWdKGQA?e=ACTmMg
UPD3: On a recent ffmpeg 6.1 adding timestamp=copy filter option also produces a file with a correct duration, but with leakage ffmpeg -y -i 5sec_silent1h_5sec.wav -acodec libopus -af silenceremove=window=0:detection=peak:stop_mode=all:start_mode=all:stop_periods=-1:stop_threshold=0:timestamp=copy 5sec_1hsilence_5sec_with_leakage.mkv. So it seems that timestamps are still not copied exactly.
