Audio streaming problems

[Michiel Konstapel]

On Monday 19 December 2022 03:38:38 (+01:00), Joel Lord via gstreamer-devel 
wrote:

 > I'm trying to take an audio feed from a microphone connected via a USB 
interface and (ideally) stream it directly out via HTTP. I want multiple 
end users to be able to get to the stream and listen to it, real time, from 
their phones. I haven't had any luck finding components that add up to 
that, but I did find how to produce a mpeg4ts stream, so I added a static 
image and have that streaming successfully, I added in a clock to have 
something changing to prove that it was working. But the audio never comes 
through.
 >
 > If I take the mpegtsmux and hlssink off the end of my pipeline and 
replace it with a filesink I can prove that my audio is working fine, but 
when I feed it to mpegtsmux and hlssink it seems to get ignored. If I have 
no image it never creates a second segment or the playlist for the stream, 
so I can't see anything at all. If I include the image the stream works but 
it seems to have no audio. I've tried 3 or 4 different audio formats, it 
doesn't complain that I have a format mismatch and it seems to be working, 
but nothing comes through.
 >
 > Using gstreamer1.0 version 1.18.4 on a Raspberry Pi 4.
 >
 > gst-launch-1.0 -v \
 > mpegtsmux name=mux ! hlssink 
playlist-root=http://stream.ek:80/stream_files 
location=/var/www/stream/stream_files/segment%05d.ts target-duration=3 
playlist-location=/var/www/stream/playlist.m3u8 \
 > filesrc location=/home/pi/EKPB.png ! decodebin ! \
 > videoconvert ! video/x-raw,format=I420 ! imagefreeze ! \
 > clockoverlay halignment=right ! x264enc ! mux. \
 > alsasrc ! audioconvert ! audio/x-raw,channels=1 ! \
 > level ! avenc_mp2fixed ! queue max-size-buffers=0 max-size-bytes=0 
max-size-time=1000000000 ! mux.
 >
 > If I take the queue out of the audio path it tosses a few warnings about 
dropping samples (a lot of samples) and gives me no faith that it will 
work. Changing the buffer settings on the queue made no difference.
 >
 > So for anyone who has made it this far, I'm quite open to better 
solutions than I've found OR fixing the one that I have that isn't working. 
I don't actually want anything but the audio feed, and I want it as close 
to 0 latency as I can get.
 >
 > Thanks for your help!
 >

Interesting! hlssink expects video key frames to know when it can start a 
new segment (which has to start with a key frame) so I don't know what 
happens with an audio only stream. At least for getting things working, 
it's probably going to be easiest to indeed have a "dummy" video track in 
there. 


I use the following for HLS audio:


... ! avenc_aac ! aacparse ! mpegtsmux


Maybe give that a go? The aacparse might be adding information needed by 
the muxer or the sink.


For x264enc you may need to specify a keyframe interval 
(key-int-max=<number of frames>) but hlssink will actively ask its upstream 
for key frames so that might not be required. Maybe also specify a 
framerate in your video caps, I don't know what the default is. After 
x264enc I also have a parser:


... ! x264enc ! h264parse config-interval=-1 ! ...



HTH,
Michiel
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