Does transcoding need special CPU/RAM ?

[djrobbie]

Im new to transcoding and I have posted several questions here regarding streaming Dreambox Satelite Channels to WAN.

I think some of my problems is just because my server thats in charge for the transcoding part is just to weak.

I have an Intel Atom CPU 330 Dual Core - 1,60 GHZ with 2, GB Memory running on a Windows 7 64 bit Asus EeeBox Pc with NVIDIA ION graphics.

Is that Computer to weak to do the transcoding job ?

What hardware do you recomend for transcoding on a general basis ?

[Greg]

There is no answer to your question.

However as a very rough guide. The pixel area, that is width x height in pixels, is the most important factor that determines the work that your computer has to do to transcode, plus many other considerations.

You have to some extent, answered your own question by your previous post...
viewtopic.php?f=4&t=83542

If your computer cannot cope beyond a scale ratio of 0.5 (given what you are trying to do??? Whatever that is?) Then given that the scale is 0.5, that is 0.5 x height and width, then this is a quarter (0.25) of the pixel area. So VERY roughly You will need four times the computing power or 1 divided 0.25 to achieve a scale ratio of 1, your expected goal?
This is perhaps a gross over simplification, but should give an idea of where you may be heading? It is not possible to to guess what "transcoding on a general basis" really means to anybody. It is a vast subject area. Choose your hardware according to anticipated needs and pocket

Throwing more cpu and ram (money) at the problem will not necessarily solve your problems, but it may help to some extent.
FYI.. I transcode-stream in h/x264 - Flash at 384 x 288 from a twin cpu Xeon computer (single core with HT each cpu) 2.4Gb at 25 fps @ 800kb bandwidth out, at a quality I find acceptable, if you find that a usefull benchmark

[alynx]

Hello,

I am trying to do something similar but with a live multicast source available in my environment , I have collected different sources of information and in my tests, a transcoding from a standard PAL (768 * 576) size video at 3Mbits/sec to a factor 0.5 downscaled video at 400kbits/sec and the transcoding takes me around 60% of one single Xeon 2Ghz core so give it a try and you will see if it works or not but it should. My configuration can be seen in this post but i haven't found a stable enough transcoding configuration corresponding to my needs :
viewtopic.php?f=14&t=83145

Greg, could you post your transcoding in order to test them in my configuration? Thanks a lot in advance !

[Greg]

OK

Re box spec on my previous post and working example.

:sout=#transcode{vcodec=h264,vb=600,deinterlace,ab=64,fps=25,width=384,height=288,acodec=mp3,samplerate=44100}:duplicate{dst=std{access=http{mime=video/x-flv},mux=ffmpeg{mux=flv},dst=0.0.0.0:8082/stream.flv},dst=display}

OS Win XP Pro
Streaming live TV via bt878 type PAL capture card (768x576) on same box
CPUs 40% to 55% av loading
Streaming out from web page via Flash player (usually Flowplayer) at 384x288
Lag 3 - 4 seconds over LAN

Final output clean with no blocking/pixelation although some occasional frame stalling, could be improved or tweaked out with some optimisation. All other settings left at default. I would normally also be including sout-keep and audio-sync. I have kept it simple for clarity.

From my own observations, I find that when indicated cpu load (Task manager or whatever) starts showing above circa 55% then the overall quality deteoriates very quickly. I believe the indicated cpu load is very averaged and does not show the inevitable short duration 100% load spikes which will mess up "on the fly" encoding .

[alynx]

Hello,

Thanks for your settings , they are quite close to mine, the big difference we have is that your source is local to your PC and mine is an already encoded video transported by IP packets and I am transcoding the audio from 48kHz to 22050 / 44100 Hz , this may create my audio desynchrinzation. I agree with the fact that the Task manager averages the instant CPU load. To see what is really going when the quality is deteriaorated , you could launch your VLC instance with the -vvv option.

[Greg]

Try
--audio-desync=<integer> ....works + or -
40ms per frame @ 25fps is a good step size

To resync your audio to video

My Ubuntu box needs a correction of about -240ms, while my XP box needs no correction.