Streaming quality

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Streaming quality

Simon
Greetings all,

I'm making my first experiments with streaming. Currently I do a live
capture of a screen region compress in real time and save the file. What I
want to do is to take that capture and send it to another machine for
storage where it will be embedded in a multi-stream container with other
sources.

So far in my experiments, I have a file I captured earlier and I'm
streaming that over to the remote system and using ffplay to view it,
rather than store it.

What I find is that the quality is trashed in the transmission, and I don't
know where to start looking for why. The original file is 720p screen
capture, and it's crisp and sharp. At the receiver, it shows what I might
describe as heavy "jpeg artifacts", that is, fuzzyness and penumbra around
all the edges of things like windows and text.

The commands I'm using are:

Receiver:
ffplay -i tcp://192.168.1.109:2000?listen

Transmitter:
ffmpeg -i <filename> -f mpegts tcp://192.168.1.109:2000

Since no codecs are mentioned, I rather assumed that the file would be
streamed "as is", but that's clearly not the case.

Can anyone point me at what I need to know to make the transmission process
not alter the quality of the image?

Many thanks,
Simon


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Simon Roberts
(303) 249 3613
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Re: Streaming quality

Carl Eugen Hoyos-2


> Am 27.06.2020 um 05:26 schrieb Simon Roberts <[hidden email]>:
>
> ffmpeg -i <filename> -f mpegts tcp://192.168.1.109:2000

Either specify a constant quantiser with “-qscale 10 -mbd 2” or a constant bitrate with “-b:v 1000k” or use “-vcodec libx264” for an encoder with a better default or “-vcodec copy” to avoid re-encoding.

Carl Eugen
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Re: Streaming quality

Simon
On Sat, Jun 27, 2020 at 1:46 AM Carl Eugen Hoyos <[hidden email]> wrote:

> > Am 27.06.2020 um 05:26 schrieb Simon Roberts <
> [hidden email]>:
> >
> > ffmpeg -i <filename> -f mpegts tcp://192.168.1.109:2000
>
> Either specify a constant quantiser with “-qscale 10 -mbd 2” or a constant
> bitrate with “-b:v 1000k” or use “-vcodec libx264” for an encoder with a
> better default or “-vcodec copy” to avoid re-encoding.
>
>
Many thanks Carl that fixed it.

I guess the inference that I had missed is that there's some kind of
default encoding going on here--it's not just a network pipe. Is that a
general case for ffmpeg, or is it specific to streaming, or perhaps this
streaming mode? (and, far less important since I doubt I'll ever want to
use it, is the encoding predictable, or does it vary by build?)

Carl Eugen
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> ffmpeg-user mailing list
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> https://ffmpeg.org/mailman/listinfo/ffmpeg-user
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Re: Streaming quality

Carl Eugen Hoyos-2
Am Sa., 27. Juni 2020 um 17:08 Uhr schrieb Simon Roberts
<[hidden email]>:

>
> On Sat, Jun 27, 2020 at 1:46 AM Carl Eugen Hoyos <[hidden email]> wrote:
>
> > > Am 27.06.2020 um 05:26 schrieb Simon Roberts <
> > [hidden email]>:
> > >
> > > ffmpeg -i <filename> -f mpegts tcp://192.168.1.109:2000
> >
> > Either specify a constant quantiser with “-qscale 10 -mbd 2” or a constant
> > bitrate with “-b:v 1000k” or use “-vcodec libx264” for an encoder with a
> > better default or “-vcodec copy” to avoid re-encoding.
> >
> >
> Many thanks Carl that fixed it.
>
> I guess the inference that I had missed is that there's some kind of
> default encoding going on here--it's not just a network pipe.

Yes, this would make no sense.

> Is that a general case for ffmpeg, or is it specific to streaming

Every format has a default encoder...

> or perhaps this streaming mode?

> (and, far less important since I doubt I'll ever want to
> use it, is the encoding predictable, or does it vary by build?)

... which in some cases depends on compilation options.

Carl Eugen
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