[FFmpeg-user] How do bitrate, FPS, and speed interact?

Moritz Barsnick barsnick at gmx.net
Wed Feb 22 16:28:39 EET 2017

On Tue, Feb 21, 2017 at 19:03:09 -0800, christina zou wrote:
> If I bump the bitrate to 1Mbps in both raspivid and FFMPEG, then FFMPEG's
> stderr tells me that it hits 1Mbps, but the speed is reported around 0.67x
> and my FPS is ~10, 2/3 of my target FPS.

That probably means that encoding to 1 Mb/s, i.e. at a higher quality,
takes more CPU resources.

> My CPU usage doesn't go above 25%, and my wifi is capable of at max 5Mbps
> upload speed, far higher than the 1Mbps video bitrate I'm attempting.

Are you sure that is the net WiFi rate you can achieve?

Are you sure that your CPU is not a four-core, and is actually at 100 %
on the one core ffmpeg is using for its main task? (You might be able
to see each core's load/CPU usage with a different view in "top", or
with "htop".)

> I'm trying to understand what is happening when Ffmpeg manages to hit my
> specified higher video bitrates, but at the sacrifice of FPS and speed. Is
> this because my internet is too slow?
> My command: http://vpaste.net/kl3Vi

a) You should have pasted that here. (It's short enough!)
b) You should have added the console output of ffmpeg.

I wonder why your setting of the bitrate changes anything at all:
> -c:v copy \
> -c:a copy \
> -b:v 1000K \

How do expect to change the (codec's encoding) bitrate if you use
"copy"? No re-encoding takes place in that case.


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