On 2016/03/25 15:03, Sreenath BH wrote:
> 1. You have to assign a gpu core by using "-gpu <number>' flag to ffmpeg.
> So we need to figure out which gpu is free and use that.
> 2. I could be wrong, but once a gpu core is assigned, it will use only
> that core and will not switch to other cores. If you have only one gpu
> core, this is not an issue.
> 3. When you run two ffmpeg instances on same gpu core, the time taken
> to transcode almost doubles.
Sorry for lacking clarity.
I actually have a working setup on my GTX660M.
However, from what I read, with lower grade GPUs the number of
simultaneous encoding instances is limited to 2 by the driver regardless
of how many cores you have. (I assume for marketing purposes)
That is exactly what I see on mine. Two realtime HD transcodes with out
sweat on a mobile GPU. Amazing... but the 3rd instance of FFmpeg fails
at start up.
If you've got 4 instances running with a build using the current SDK, I
am assuming you have a non-lower-end card that will run even more.
Would you mind sharing what GPU you use?
The nvidia encoder, when used for transcoding, creates files with high
bitrates(and large file sizes) as compared with libx264 s/w codec. I
have not found ways to control bitrate without loss of picture
quality.
I was able to gain some control using the -maxrate option.
I see what you mean about quality and agree with you.
For the particular application in mind, I found the balance in bitrate
v.s. quality acceptable if it allows us to transcode 10s of live streams
in one box... hopefully on an ordinary desktop PC.
--
David Shimamoto
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