====== RTL SDR streaming ======

===== RTP stream =====

When is -M modulation set to fm, -s means width of modulation and it has to be the same as first -ar which measn sample rate of source.  
RTP needs to by pointed to special sever machine where we can listen.

<code>
rtl_fm -f 403480405 -M fm -s 10000 -A std -l 0 | ffmpeg -f s16le -ac 1 -ar 10000 -i pipe:0 -acodec pcm_s16be -ar 44100 -f rtp rtp://192.168.1.103:1234
</code>

Put link to VLC playlist:
<code>
rtp://192.168.1.103:1234
</code>

pros:
  * uncompressed
cons:
  * not tested via internet

===== mp3 stream =====

For mp3 streaming is required ffstream. Example of ffstream configuration (/etc/ffserver.conf):
<code>
# Port on which the server is listening. You must select a different
# port from your standard HTTP web server if it is running on the same
# computer.
HTTPPort 8090

# Address on which the server is bound. Only useful if you have
# several network interfaces.
HTTPBindAddress 0.0.0.0

# Number of simultaneous HTTP connections that can be handled. It has
# to be defined *before* the MaxClients parameter, since it defines the
# MaxClients maximum limit.
MaxHTTPConnections 2000

# Number of simultaneous requests that can be handled. Since FFServer
# is very fast, it is more likely that you will want to leave this high
# and use MaxBandwidth, below.
MaxClients 1000

# This the maximum amount of kbit/sec that you are prepared to
# consume when streaming to clients.
MaxBandwidth 1000

# Access log file (uses standard Apache log file format)
# '-' is the standard output.
CustomLog -

##################################################################
# Definition of the live feeds. Each live feed contains one video
# and/or audio sequence coming from an ffmpeg encoder or another
# ffserver. This sequence may be encoded simultaneously with several
# codecs at several resolutions.

<Feed feed1.ffm>

# You must use 'ffmpeg' to send a live feed to ffserver. In this
# example, you can type:
#
# ffmpeg http://localhost:8090/feed1.ffm

# ffserver can also do time shifting. It means that it can stream any
# previously recorded live stream. The request should contain:
# "http://xxxx?date=[YYYY-MM-DDT][[HH:]MM:]SS[.m...]".You must specify
# a path where the feed is stored on disk. You also specify the
# maximum size of the feed, where zero means unlimited. Default:
# File=/tmp/feed_name.ffm FileMaxSize=5M
File /tmp/feed1.ffm
FileMaxSize 200K

# You could specify
# ReadOnlyFile /saved/specialvideo.ffm
# This marks the file as readonly and it will not be deleted or updated.

# Specify launch in order to start ffmpeg automatically.
# First ffmpeg must be defined with an appropriate path if needed,
# after that options can follow, but avoid adding the http:// field
#Launch ffmpeg

# Only allow connections from localhost to the feed.
ACL allow 127.0.0.1

</Feed>

# MP3 audio

<Stream test.mp3>
Feed feed1.ffm
Format mp2
AudioCodec libmp3lame
AudioBitRate 512
AudioChannels 1
AudioSampleRate 44100
NoVideo
</Stream>

# Ogg Vorbis audio

#<Stream test.ogg>
#Feed feed1.ffm
#Metadata title "Stream title"
#AudioBitRate 64
#AudioChannels 2
#AudioSampleRate 44100
#NoVideo
#</Stream>

##################################################################
# Special streams

# Server status

<Stream stat.html>
Format status

# Only allow local people to get the status
ACL allow localhost
ACL allow 192.168.0.0 192.168.255.255

#FaviconURL http://pond1.gladstonefamily.net:8080/favicon.ico
</Stream>


# Redirect index.html to the appropriate site

<Redirect index.html>
URL http://www.ffmpeg.org/
</Redirect>
</code>

Strat server:
<code>
ffserver
</code>

Start rtl_sdr and stream mp3 to feed1:
<code>
 rtl_fm -f 96.5M -M fm -s 170k -A std -l 0 | ffmpeg -f s16le -ac 1 -ar 170000 -i pipe:0 -acodec libmp3lame -ar 44100 http://localhost:8090/feed1.ffm
</code>

Put link to VLC playlist:
<code>
http://192.168.88.55:8090/test.mp3
</code>

pros:
  * Should work via internet
  * multi client access
cons:
  * compressed

http://kmkeen.com/rtl-demod-guide/
https://medium.com/@luigifcruz/listening-live-fm-radio-over-the-network-with-rtl-sdr-2349c5abe878
https://lansley.com/2014/09/27/using-rtl_fm-and-ffmpeg-to-stream-radio-audio-over-network/
https://ffmpeg.org/ffserver.html#Configuration-file-syntax
https://www.ffmpeg.org/sample.html