input:
ffmpeg -i 'udp://@xxx' -crf 30 -preset ultrafast -acodec aac -strict experimental -ar 44100 -ac 2 -b:a 96k -vcodec libx264 -r 25 -b:v 500k -f flv 'rtmp://xxxx'

output:
[libx264 @ 0x275d080] using SAR=64/45
[libx264 @ 0x275d080] using cpu capabilities: MMX2 SSE2Fast SSSE3 Cache64 SlowShuffle
[libx264 @ 0x275d080] profile Constrained Baseline, level 3.0
[libx264 @ 0x275d080] 264 - core 142 - H.264/MPEG-4 AVC codec - Copyleft 2003-2014 - http://www.videolan.org/x264.html - options: cabac=0 ref=1 deblock=0:0:0 analyse=0:0 me=dia subme=0 psy=1 psy_rd=1.00:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=0 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=0 threads=12 lookahead_threads=2 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=0 weightp=0 keyint=250 keyint_min=25 scenecut=0 intra_refresh=0 rc=crf mbtree=0 crf=30.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=0
Output #0, flv, to 'rtmp://xxxx':
  Metadata:
    encoder         : Lavf55.33.101
    Stream #0:0: Video: h264 (libx264) ([7][0][0][0] / 0x0007), yuv420p, 720x576 [SAR 64:45 DAR 16:9], q=-1--1, 1200 kb/s, 1k tbn, 25 tbc
    Stream #0:1: Audio: aac ([10][0][0][0] / 0x000A), 44100 Hz, stereo, fltp, 96 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (mpeg2video -> libx264)
  Stream #0:1 -> #0:1 (mp2 -> aac)
Press [q] to stop, [?] for help
frame=25517 fps= 25 q=32.0 size=  249611kB time=00:17:00.83 bitrate=2003.1kbits/s