- <div class="title"><a href="http://people.skolelinux.org/pere/blog/Streaming_the_Linux_desktop_to_Kodi_using_VLC_and_RTSP.html">Streaming the Linux desktop to Kodi using VLC and RTSP</a></div>
- <div class="date">12th July 2018</div>
- <div class="body"><p>PS: See
-<ahref="http://people.skolelinux.org/pere/blog/Simple_streaming_the_Linux_desktop_to_Kodi_using_GStreamer_and_RTP.html">the
-followup post</a> for a even better approach.</p>
-
-<p>A while back, I was asked by a friend how to stream the desktop to
-my projector connected to Kodi. I sadly had to admit that I had no
-idea, as it was a task I never had tried. Since then, I have been
-looking for a way to do so, preferable without much extra software to
-install on either side. Today I found a way that seem to kind of
-work. Not great, but it is a start.</p>
-
-<p>I had a look at several approaches, for example
-<a href="https://github.com/mfoetsch/dlna_live_streaming">using uPnP
-DLNA as described in 2011</a>, but it required a uPnP server, fuse and
-local storage enough to store the stream locally. This is not going
-to work well for me, lacking enough free space, and it would
-impossible for my friend to get working.</p>
-
-<p>Next, it occurred to me that perhaps I could use VLC to create a
-video stream that Kodi could play. Preferably using
-broadcast/multicast, to avoid having to change any setup on the Kodi
-side when starting such stream. Unfortunately, the only recipe I
-could find using multicast used the rtp protocol, and this protocol
-seem to not be supported by Kodi.</p>
-
-<p>On the other hand, the rtsp protocol is working! Unfortunately I
-have to specify the IP address of the streaming machine in both the
-sending command and the file on the Kodi server. But it is showing my
-desktop, and thus allow us to have a shared look on the big screen at
-the programs I work on.</p>
-
-<p>I did not spend much time investigating codeces. I combined the
-rtp and rtsp recipes from
-<a href="https://wiki.videolan.org/Documentation:Streaming_HowTo/Command_Line_Examples/">the
-VLC Streaming HowTo/Command Line Examples</a>, and was able to get
-this working on the desktop/streaming end.</p>
-
-<blockquote><pre>
-vlc screen:// --sout \
- '#transcode{vcodec=mp4v,acodec=mpga,vb=800,ab=128}:rtp{dst=projector.local,port=1234,sdp=rtsp://192.168.11.4:8080/test.sdp}'
-</pre></blockquote>
-
-<p>I ssh-ed into my Kodi box and created a file like this with the
-same IP address:</p>
-
-<blockquote><pre>
-echo rtsp://192.168.11.4:8080/test.sdp \
- > /storage/videos/screenstream.m3u
-</pre></blockquote>
-
-<p>Note the 192.168.11.4 IP address is my desktops IP address. As far
-as I can tell the IP must be hardcoded for this to work. In other
-words, if someone elses machine is going to do the steaming, you have
-to update screenstream.m3u on the Kodi machine and adjust the vlc
-recipe. To get started, locate the file in Kodi and select the m3u
-file while the VLC stream is running. The desktop then show up in my
-big screen. :)</p>
-
-<p>When using the same technique to stream a video file with audio,
-the audio quality is really bad. No idea if the problem is package
-loss or bad parameters for the transcode. I do not know VLC nor Kodi
-enough to tell.</p>
-
-<p><strong>Update 2018-07-12</strong>: Johannes Schauer send me a few
-succestions and reminded me about an important step. The "screen:"
-input source is only available once the vlc-plugin-access-extra
-package is installed on Debian. Without it, you will see this error
-message: "VLC is unable to open the MRL 'screen://'. Check the log
-for details." He further found that it is possible to drop some parts
-of the VLC command line to reduce the amount of hardcoded information.
-It is also useful to consider using cvlc to avoid having the VLC
-window in the desktop view. In sum, this give us this command line on
-the source end
-
-<blockquote><pre>
-cvlc screen:// --sout \
- '#transcode{vcodec=mp4v,acodec=mpga,vb=800,ab=128}:rtp{sdp=rtsp://:8080/}'
-</pre></blockquote>
-
-<p>and this on the Kodi end<p>
-
-<blockquote><pre>
-echo rtsp://192.168.11.4:8080/ \
- > /storage/videos/screenstream.m3u
-</pre></blockquote>
-
-<p>Still bad image quality, though. But I did discover that streaming
-a DVD using dvdsimple:///dev/dvd as the source had excellent video and
-audio quality, so I guess the issue is in the input or transcoding
-parts, not the rtsp part. I've tried to change the vb and ab
-parameters to use more bandwidth, but it did not make a
-difference.</p>
-
-<p>I further received a suggestion from Einar Haraldseid to try using
-gstreamer instead of VLC, and this proved to work great! He also
-provided me with the trick to get Kodi to use a multicast stream as
-its source. By using this monstrous oneliner, I can stream my desktop
-with good video quality in reasonable framerate to the 239.255.0.1
-multicast address on port 1234:
-
-<blockquote><pre>
-gst-launch-1.0 ximagesrc use-damage=0 ! video/x-raw,framerate=30/1 ! \
- videoconvert ! queue2 ! \
- x264enc bitrate=8000 speed-preset=superfast tune=zerolatency qp-min=30 \
- key-int-max=15 bframes=2 ! video/x-h264,profile=high ! queue2 ! \
- mpegtsmux alignment=7 name=mux ! rndbuffersize max=1316 min=1316 ! \
- udpsink host=239.255.0.1 port=1234 ttl-mc=1 auto-multicast=1 sync=0 \
- pulsesrc device=$(pactl list | grep -A2 'Source #' | \
- grep 'Name: .*\.monitor$' | cut -d" " -f2|head -1) ! \
- audioconvert ! queue2 ! avenc_aac ! queue2 ! mux.
-</pre></blockquote>
-
-<p>and this on the Kodi end<p>
-
-<blockquote><pre>
-echo udp://@239.255.0.1:1234 \
- > /storage/videos/screenstream.m3u
-</pre></blockquote>
-
-<p>Note the trick to pick a valid pulseaudio source. It might not
-pick the one you need. This approach will of course lead to trouble
-if more than one source uses the same multicast port and address.
-Note the ttl-mc=1 setting, which limit the multicast packages to the
-local network. If the value is increased, your screen will be
-broadcasted further, one network "hop" for each increase (read up on
-multicast to learn more. :)!</p>
-
-<p>Having cracked how to get Kodi to receive multicast streams, I
-could use this VLC command to stream to the same multicast address.
-The image quality is way better than the rtsp approach, but gstreamer
-seem to be doing a better job.</p>
-
-<blockquote><pre>
-cvlc screen:// --sout '#transcode{vcodec=mp4v,acodec=mpga,vb=800,ab=128}:rtp{mux=ts,dst=239.255.0.1,port=1234,sdp=sap}'
-</pre></blockquote>
+ <div class="title"><a href="http://people.skolelinux.org/pere/blog/Measuring_the_speaker_frequency_response_using_the_AUDMES_free_software_GUI___nice_free_software.html">Measuring the speaker frequency response using the AUDMES free software GUI - nice free software</a></div>
+ <div class="date">22nd October 2018</div>
+ <div class="body"><p><img src="http://people.skolelinux.org/pere/blog/images/2018-10-22-audmes-measure-speakers.png" align="right" width="40%"/></p>
+
+<p>My current home stereo is a patchwork of various pieces I got on
+flee markeds over the years. It is amazing what kind of equipment
+show up there. I've been wondering for a while if it was possible to
+measure how well this equipment is working together, and decided to
+see how far I could get using free software. After trawling the web I
+came across an article from DIY Audio and Video on
+<a href="https://www.diyaudioandvideo.com/Tutorial/SpeakerResponseTesting/">Speaker
+Testing and Analysis</a> describing how to test speakers, and it listing
+several software options, among them
+<a href="https://sourceforge.net/projects/audmes/">AUDio MEasurement
+System (AUDMES)</a>. It is the only free software system I could find
+focusing on measuring speakers and audio frequency response. In the
+process I also found an interesting article from NOVO on
+<a href="http://novo.press/understanding-speaker-specifications-and-frequency-response/">Understanding
+Speaker Specifications and Frequency Response</a> and an article from
+ecoustics on
+<a href="https://www.ecoustics.com/articles/understanding-speaker-frequency-response/">Understanding
+Speaker Frequency Response</a>, with a lot of information on what to
+look for and how to interpret the graphs. Armed with this knowledge,
+I set out to measure the state of my speakers.</p>
+
+<p>The first hurdle was that AUDMES hadn't seen a commit for 10 years
+and did not build with current compilers and libraries. I got in
+touch with its author, who no longer was spending time on the program
+but gave me write access to the subversion repository on Sourceforge.
+The end result is that now the code build on Linux and is capable of
+saving and loading the collected frequency response data in CSV
+format. The application is quite nice and flexible, and I was able to
+select the input and output audio interfaces independently. This made
+it possible to use a USB mixer as the input source, while sending
+output via my laptop headphone connection. I lacked the hardware and
+cabling to figure out a different way to get independent cabling to
+speakers and microphone.</p>
+
+<p>Using this setup I could see how a large range of high frequencies
+apparently were not making it out of my speakers. The picture show
+the frequency response measurement of one of the speakers. Note the
+frequency lines seem to be slightly misaligned, compared to the CSV
+output from the program. I can not hear several of these are high
+frequencies, according to measurement from
+<a href="http://freehearingtestsoftware.com">Free Hearing Test
+Software</a>, an freeware system to measure your hearing (still
+looking for a free software alternative), so I do not know if they are
+coming out out the speakers. I thus do not quite know how to figure
+out if the missing frequencies is a problem with the microphone, the
+amplifier or the speakers, but I managed to rule out the audio card in my
+PC by measuring my Bose noise canceling headset using its own
+microphone. This setup was able to see the high frequency tones, so
+the problem with my stereo had to be in the amplifier or speakers.</p>
+
+<p>Anyway, to try to role out one factor I ended up picking up a new
+set of speakers at a flee marked, and these work a lot better than the
+old speakers, so I guess the microphone and amplifier is OK. If you
+need to measure your own speakers, check out AUDMES. If more people
+get involved, perhaps the project could become good enough to
+<a href="https://bugs.debian.org/910876">include in Debian</a>? And if
+you know of some other free software to measure speakers and amplifier
+performance, please let me know. I am aware of the freeware option
+<a href="https://www.roomeqwizard.com/">REW</a>, but I want something
+that can be developed also when the vendor looses interest.</p>
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