Recording error/failure with parameters.

[Ian Davidson]

Thanks Tim, I have now got a command which is syntactically correct.

May I make a comment about the GStreamer Documentation?


On the GStreamer web site it says "Application Development Manual (*Read 
this first*) " - so that would seem to be the place to start if you want 
to learn about Gstreamer.

Very early in the document (section 2.1), it says that "The programmer 
can use an extensive set of powerful tools to create media pipelines 
without writing a single line of code. " That is good to know and is 
brought about by the library of 'Plug-ins'.

But -- then as you continue to read the manual, you are thrown heavily 
into programming. Straight away.


Might I suggest that very early on you have mention of gst-launch -- 
since, using that you can do things without having to write a single 
line of coding. However, the chapter on gst-launch itself is not an 
easy-to-read chapter: It starts with a 'simple commandline' and then 
shows a more complex one -- but without any explanation. If we take the 
first example

gst-launch filesrc location=hello.mp3 ! mad ! audioresample ! osssink

you could then describe what is happening. e.g.

gst-launch is a program which enables the user to construct pipelines 
using command-line parameters.

Filesrc is an element (or a plugin) -- in this case it will read data 
from a file and needs to know the name of the file to open. It will 
output the data so as to be the source for the next element in the 
pipe-line.

The "!" symbol separates the first element from the next.

mad is the next element in the pipe-line: It will decode mp3 data. It 
picks up the source provided by the previous element and then outputs 
the decoded data for the next element in the pipe-line.

Once again, a "!" symbol separates the elements.

audioresample resamples the Audio. (I don't know why this is a benefit 
-- it could be explained)

Another "!"

osssink takes the audio signal and sends it to an output device which 
supports (or is supported by) OSS.

The second example could then be similarly explained -- which would be a 
useful exercise since the single vob file is being demuxed with part of 
the data going one way and the rest another.

A reference, at this point to the Overview of available plug-ins would 
be beneficial.

Perhaps an example where more options need to be specified could also be 
explained.

Then you can say that, if you need to build this into an application, 
you can do the same stuff with code and if you need to do something 
which is not currently supported, you can write your own plug-in -- so 
read on...

I hope this is useful

Ian


On 27/11/2012 22:52, Tim-Philipp Müller wrote:
> On Tue, 2012-11-27 at 22:48 +0000, Ian Davidson wrote:
>
> Hi,
>
>> I changed the Test Sources to use what I hoped would be real inputs
>> [ian at localhost ~]$ gst-launch-1.0 --gst-debug-level=4 v4l2src
>> 'video/x-raw,format=(string)I420,width=320,height=240,framerate=(fraction)25/1'
>> ! queue ! mux. alsasrc ! audioconvert !
>> 'audio/x-raw,rate=44100,channels=2' ! queue ! mux. avimux name=mux !
>> filesink location=test.avi
> You seem to be missing a ! between v4l2src and the filter caps here.
>
> Cheers
>   -Tim
>

-- 
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Ian Davidson
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