FFMPEG: Fast encoding optimizations (help needed)

There's a TV channel, broadcasting over IPADSL, I need to watch for 2 hours each saturday night.
For many reasons, I can't access it from my new place.

At my office, I have that channel available and a synology NAS with a ARM CPU.
I can VPN that network and access the IPADSL stream.

Thing is, the max upload speed at said office is 115KB/s.

So I need to transcode the stream in realtime and access it from my home.

I've done some testing, transcoding in realtime is possible and the result is more than enough for my needs. I need to transcode the video to around 800kb/s sound included and try to keep sound bitrate at 192kb/s if possible since sound is more important than image in that case.

The testing has been done with fairly low end computer by today's standards, using VLC transcoding/broadcasting.
But I can't use that comp as a longterm solution.

Since I have full access to the nas, the idea is that I use it. But its computing power is far below that of the test comp I used obviously.

Hence the need for help in finding the best set of options to optimize transcoding speed.

Source stats reported by ffmpeg (1 minute sample):

Code:

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Duration: 00:00:59.21, start: 13060.597889, bitrate: 3549 kb/s
  Program 1
    Stream #0.0[0x44]: Video: mpeg2video (Main), yuv420p, 720x576 [PAR  64:45 DAR 16:9], 3100 kb/s, 26.89 fps, 25 tbr, 90k tbn, 50 tbc
    Stream #0.1[0x45](fra): Audio: mp2, 48000 Hz, stereo, s16, 192 kb/s

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With FFMPEG default settings, I get 7-8 FPS processing speed. When I first got that number, I was quite surprised as I thought I would get a much lower "score".

Stats from media for the test sample result:

Code:

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General
Complete name                  : \\192.168.0.33\public\test.avi
Format                        : AVI
Format/Info                    : Audio Video Interleave
File size                      : 1.48 MiB
Duration                      : 18s 80ms
Overall bit rate              : 687 Kbps
Writing application            : Lavf52.108.0

Video
ID                            : 0
Format                        : MPEG-4 Visual
Format profile                : Simple@L1
Format settings, BVOP          : No
Format settings, QPel          : No
Format settings, GMC          : No warppoints
Format settings, Matrix        : Default (H.263)
Codec ID                      : FMP4
Duration                      : 18s 80ms
Bit rate                      : 484 Kbps
Width                          : 720 pixels
Height                        : 576 pixels
Display aspect ratio          : 16:9
Frame rate                    : 25.000 fps
Standard                      : PAL
Color space                    : YUV
Chroma subsampling            : 4:2:0
Bit depth                      : 8 bits
Scan type                      : Progressive
Compression mode              : Lossy
Bits/(Pixel*Frame)            : 0.047
Stream size                    : 1.04 MiB (71%)
Writing library                : Lavc52.120.0

Audio
ID                            : 1
Format                        : MPEG Audio
Format version                : Version 1
Format profile                : Layer 2
Codec ID                      : 50
Duration                      : 17s 472ms
Bit rate mode                  : Constant
Bit rate                      : 192 Kbps
Channel(s)                    : 2 channels
Sampling rate                  : 48.0 KHz
Compression mode              : Lossy
Stream size                    : 410 KiB (27%)
Alignment                      : Aligned on interleaves
Interleave, duration          : 25 ms (0.62 video frame)
Interleave, preload duration  : 528 ms

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ffmpeg -formats result:

Code:

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ffmpeg version UNKNOWN, Copyright (c) 2000-2011 the FFmpeg developers
  built on Sep  4 2011 02:28:29 with gcc 4.2.1
  configuration: --arch=arm --target-os=linux  --cross-prefix=/usr/local/arm-none-linux-gnueabi/bin/arm-none-linux-gnueabi-  --enable-cross-compile --enable-optimizations --disable-yasm  --disable-altivec --enable-pic --enable-shared --disable-static  --disable-swscale-alpha --disable-ffserver --disable-ffplay  --enable-libmp3lame
  libavutil    50. 40. 1 / 50. 40. 1
  libavcodec  52.120. 0 / 52.120. 0
  libavformat  52.108. 0 / 52.108. 0
  libavdevice  52.  4. 0 / 52.  4. 0
  libavfilter  1. 77. 0 /  1. 77. 0
  libswscale    0. 14. 0 /  0. 14. 0
File formats:
 D. = Demuxing supported
 .E = Muxing supported
 --
  E 3g2            3GP2 format
  E 3gp            3GP format
 D  4xm            4X Technologies format
 D  IFF            IFF format
 D  ISS            Funcom ISS format
 D  MTV            MTV format
 DE RoQ            raw id RoQ format
  E a64            a64 - video for Commodore 64
 D  aac            raw ADTS AAC
 DE ac3            raw AC-3
  E adts            ADTS AAC
 D  aea            MD STUDIO audio
 DE aiff            Audio IFF
 DE alaw            PCM A-law format
 DE amr            3GPP AMR file format
 D  anm            Deluxe Paint Animation
 D  apc            CRYO APC format
 D  ape            Monkey's Audio
 D  applehttp      Apple HTTP Live Streaming format
 DE asf            ASF format
  E asf_stream      ASF format
 DE ass            Advanced SubStation Alpha subtitle format
 DE au              SUN AU format
 DE avi            AVI format
  E avm2            Flash 9 (AVM2) format
 D  avs            AVS format
 D  bethsoftvid    Bethesda Softworks VID format
 D  bfi            Brute Force & Ignorance
 D  bink            Bink
 D  c93            Interplay C93
 D  caf            Apple Core Audio Format
 DE cavsvideo      raw Chinese AVS video
 D  cdg            CD Graphics Format
  E crc            CRC testing format
 DE daud            D-Cinema audio format
 D  dfa            Chronomaster DFA
 DE dirac          raw Dirac
 DE dnxhd          raw DNxHD (SMPTE VC-3)
 D  dsicin          Delphine Software International CIN format
 DE dts            raw DTS
 DE dv              DV video format
 D  dv1394          DV1394 A/V grab
  E dvd            MPEG-2 PS format (DVD VOB)
 D  dxa            DXA
 D  ea              Electronic Arts Multimedia Format
 D  ea_cdata        Electronic Arts cdata
 DE eac3            raw E-AC-3
 DE f32be          PCM 32 bit floating-point big-endian format
 DE f32le          PCM 32 bit floating-point little-endian format
 DE f64be          PCM 64 bit floating-point big-endian format
 DE f64le          PCM 64 bit floating-point little-endian format
 D  fbdev          Linux framebuffer
 DE ffm            FFM (FFserver live feed) format
 DE ffmetadata      FFmpeg metadata in text format
 D  film_cpk        Sega FILM/CPK format
 DE filmstrip      Adobe Filmstrip
 DE flac            raw FLAC
 D  flic            FLI/FLC/FLX animation format
 DE flv            FLV format
  E framecrc        framecrc testing format
  E framemd5        Per-frame MD5 testing format
 DE g722            raw G.722
  E gif            GIF Animation
 D  gsm            raw GSM
 DE gxf            GXF format
 DE h261            raw H.261
 DE h263            raw H.263
 DE h264            raw H.264 video format
 D  idcin          id Cinematic format
 DE image2          image2 sequence
 DE image2pipe      piped image2 sequence
 D  ingenient      raw Ingenient MJPEG
 D  ipmovie        Interplay MVE format
  E ipod            iPod H.264 MP4 format
 D  iv8            A format generated by IndigoVision 8000 video server
 DE ivf            On2 IVF
 D  jv              Bitmap Brothers JV
 D  lmlm4          lmlm4 raw format
 D  lxf            VR native stream format (LXF)
 DE m4v            raw MPEG-4 video format
  E matroska        Matroska file format
 D  matroska,webm  Matroska/WebM file format
  E md5            MD5 testing format
 DE microdvd        MicroDVD subtitle format
 DE mjpeg          raw MJPEG video
 DE mlp            raw MLP
 D  mm              American Laser Games MM format
 DE mmf            Yamaha SMAF
  E mov            MOV format
 D  mov,mp4,m4a,3gp,3g2,mj2 QuickTime/MPEG-4/Motion JPEG 2000 format
  E mp2            MPEG audio layer 2
 DE mp3            MPEG audio layer 3
  E mp4            MP4 format
 D  mpc            Musepack
 D  mpc8            Musepack SV8
 DE mpeg            MPEG-1 System format
  E mpeg1video      raw MPEG-1 video
  E mpeg2video      raw MPEG-2 video
 DE mpegts          MPEG-2 transport stream format
 D  mpegtsraw      MPEG-2 raw transport stream format
 D  mpegvideo      raw MPEG video
  E mpjpeg          MIME multipart JPEG format
 D  msnwctcp        MSN TCP Webcam stream
 DE mulaw          PCM mu-law format
 D  mvi            Motion Pixels MVI format
 DE mxf            Material eXchange Format
  E mxf_d10        Material eXchange Format, D-10 Mapping
 D  mxg            MxPEG clip file format
 D  nc              NC camera feed format
 D  nsv            Nullsoft Streaming Video
  E null            raw null video format
 DE nut            NUT format
 D  nuv            NuppelVideo format
 DE ogg            Ogg
 D  oma            Sony OpenMG audio
 DE oss            Open Sound System playback
 D  pmp            Playstation Portable PMP format
  E psp            PSP MP4 format
 D  psxstr          Sony Playstation STR format
 D  pva            TechnoTrend PVA file and stream format
 D  qcp            QCP format
 D  r3d            REDCODE R3D format
 DE rawvideo        raw video format
  E rcv            VC-1 test bitstream
 D  rl2            RL2 format
 DE rm              RealMedia format
 D  rpl            RPL/ARMovie format
 DE rso            Lego Mindstorms RSO format
 DE rtp            RTP output format
 DE rtsp            RTSP output format
 DE s16be          PCM signed 16 bit big-endian format
 DE s16le          PCM signed 16 bit little-endian format
 DE s24be          PCM signed 24 bit big-endian format
 DE s24le          PCM signed 24 bit little-endian format
 DE s32be          PCM signed 32 bit big-endian format
 DE s32le          PCM signed 32 bit little-endian format
 DE s8              PCM signed 8 bit format
 DE sap            SAP output format
 D  sdp            SDP
 D  shn            raw Shorten
 D  siff            Beam Software SIFF
 D  smk            Smacker video
 D  sol            Sierra SOL format
 DE sox            SoX native format
 DE spdif          IEC 61937 (used on S/PDIF - IEC958)
 DE srt            SubRip subtitle format
  E svcd            MPEG-2 PS format (VOB)
 DE swf            Flash format
 D  thp            THP
 D  tiertexseq      Tiertex Limited SEQ format
 D  tmv            8088flex TMV
 DE truehd          raw TrueHD
 D  tta            True Audio
 D  tty            Tele-typewriter
 D  txd            Renderware TeXture Dictionary
 DE u16be          PCM unsigned 16 bit big-endian format
 DE u16le          PCM unsigned 16 bit little-endian format
 DE u24be          PCM unsigned 24 bit big-endian format
 DE u24le          PCM unsigned 24 bit little-endian format
 DE u32be          PCM unsigned 32 bit big-endian format
 DE u32le          PCM unsigned 32 bit little-endian format
 DE u8              PCM unsigned 8 bit format
 D  vc1            raw VC-1
 D  vc1test        VC-1 test bitstream format
  E vcd            MPEG-1 System format (VCD)
 D  video4linux    Video4Linux device grab
 D  video4linux2    Video4Linux2 device grab
 D  vmd            Sierra VMD format
  E vob            MPEG-2 PS format (VOB)
 DE voc            Creative Voice file format
 D  vqf            Nippon Telegraph and Telephone Corporation (NTT) TwinVQ
 D  w64            Sony Wave64 format
 DE wav            WAV format
 D  wc3movie        Wing Commander III movie format
  E webm            WebM file format
 D  wsaud          Westwood Studios audio format
 D  wsvqa          Westwood Studios VQA format
 D  wtv            Windows Television (WTV)
 D  wv              WavPack
 D  xa              Maxis XA File Format
 D  xwma            Microsoft xWMA
 D  yop            Psygnosis YOP Format
 DE yuv4mpegpipe    YUV4MPEG pipe format

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I tried halving height and width, setting 15FPS for the output and many codecs, but never really got over 9FPS... only when I divided height and width by 4 and got 14 FPS. But it's not very watchable anymore.

I can accept halving height and width
I can accept pixelisation
I can accept going to 20FPS for the output
If I have no other option I can accept going to 128kb/s for the audio although transcoding it would impact processing speed I guess.

The resulting file must be 800kb/s max and I need transcoding settings that allow for maximum speed. I know that maybe it's impossible to cope with all those conditions on such a slow system (DS109) but I wish to try.

Thanks for reading ;) Even more if you can and do help :D