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I have a MPEG Audio MPEG1 layer 2 stream on UDP without TS header and when I try to play it, VLC tell me that it is a Audio flow and that it uses codec mpga but nothing makes sound !?!
I tryed with a video stream and it worked so I don't understand ...

following, the messages of vlc trying to play audio stream :

main debug: adding playlist item `udp://@:1235' ( udp://@:1235 )
main debug: creating new input thread
main debug: waiting for thread completion
main debug: `udp://@:1235' gives access `udp' demux `' path `@:1235'
main debug: demux2_New: access='udp' demux='' path='@:1235'
main debug: looking for access_demux module
main debug: probing 0 candidates
main debug: thread 4084 (input) created at priority 1 (src/input/input.c:228)
main warning: no access_demux module matched "udp"
main debug: access2_New: access='udp' path='@:1235'
main debug: looking for access2 module
main debug: probing 5 candidates
access_udp debug: opening server=:0 local=:1235
main debug: net: connecting to ':0@:1235'
main debug: looking for network module
main debug: probing 2 candidates
main debug: using network module "ipv4"
main debug: unlocking module "ipv4"
main debug: using access2 module "access_udp"
main debug: pre buffering
access_udp debug: no RTP header detected
main debug: received first data for our buffer
main debug: prebuffering done 1472 bytes in 0s - 13 kbytes/s
main debug: demux2_New: access='udp' demux='' path='@:1235'
main debug: looking for demux2 module
main debug: probing 34 candidates
mp4 warning: MP4 plugin discarded (not a valid file)
avi warning: avi module discarded (invalid header)
asf warning: ASF plugin discarded (not a valid file)
flac warning: flac module discarded (no startcode)
mpgv warning: ES module discarded (no startcode)
main debug: looking for id3 module
main debug: probing 2 candidates
id3tag debug: checking for ID3 tag
main debug: using id3 module "id3tag"
main debug: unlocking module "id3tag"
aac warning: AAC module discarded
sap warning: SDP (UDP) module discarded
livedotcom warning: SDP module discarded
mkv warning: matroska module discarded (invalid header 0x978de198)
ogg warning: ogg module discarded (invalid header)
real warning: Real module discarded
pva warning: PVA module discarded
nsv warning: NSV module discarded
aiff warning: AIFF module discarded
playlist warning: old import module discarded: invalid file
playlist warning: pls import module discarded
au warning: AU module discarded
ts warning: TS module discarded
mod warning: MOD module discarded (path=@:1235)
ffmpeg debug: couldn't guess format
ps warning: this does not look like an MPEG PS stream, continuing anyway
main debug: using demux2 module "ps"
main debug: `udp://@:1235' sucessfully opened
ps warning: garbage at input
ps warning: garbage at input
main debug: Selecting program id=0
main debug: looking for decoder module
main debug: probing 23 candidates
main debug: using decoder module "mpeg_audio"
main debug: thread 4352 (decoder) created at priority 2 (src/input/decoder.c:157)
ps warning: garbage at input
ps warning: garbage at input
ps warning: garbage at input
ps warning: garbage at input
ps warning: garbage at input
ps warning: garbage at input
ps warning: garbage at input
ps warning: garbage at input
ps warning: garbage at input
ps warning: garbage at input
main error: recv() failed. Increase the mtu size (--mtu option)
access_udp debug: increasing MTU to 3000
ps warning: garbage at input
ps warning: garbage at input
ps warning: garbage at input
ps warning: garbage at input
ps warning: garbage at input
ps warning: garbage at input

PES isn't a proper format. it doesn't contain time information. Without that, VLC cannot properly play it back.
You should use either TS or PS.