[Libav-user] invalid AVPacket size in av_read_frame usage.

[daggs]

Greetings,

> Sent: Monday, April 27, 2015 at 11:20 AM
> From: "Carl Eugen Hoyos" <cehoyos at ag.or.at>
> To: libav-user at ffmpeg.org
> Subject: Re: [Libav-user] invalid AVPacket size in av_read_frame usage.
>
> daggs <daggs at ...> writes:
> 
> > > > I'm writing a program that needs to sample the 
> > > > screen in bgra format. the problem is what I try 
> > > > to read an av frame, I get this error:
> > > > [rawvideo  <at>  0x1403aa0] Invalid buffer size, 
> > > > packet size 1228800 < expected frame_size 8294400
> > > 
> > > Where does the packet come from that you pass to 
> > > the video decode function?
> 
> ?

I'm using the x11grab module set to my desktop and grab the packets using av_read_frame call.

> 
> > > What is the resolution of the video that you 
> > > want to decode?
> > 
> > that is a raw packet of a 1920x1080 screen.
> 
> 1920 x 1080 x 4 = 8,294,400 so the error seems correct 
> to me.
> 
> [...]

but that isn't what I've asked, I see that error and tried to increase the buffer using av_new_packet but it doesn't work so I'm trying to understand what I'm doing wrong.

> 
> > which encodes it to the required format (libx264rbg).
> > 
> > if I'm not mistaken, scaling the frame to yuv420p 
> > will drop the quality of the frame which I don't 
> > want to have.
> 
> That doesn't explain why you need the rawvideo decoder.

I did, I don't want the thread that grabs the screen do encode the frame, so I grab it raw and pass it to another thread which encodes it.

> Or are you using libavformat to capture the screen?
> (You didn't say so.)
> 

I've searched the net and found some examples and projects that grabs screen in similar way.
I haven't found any example in the ffmpeg docs regarding screen capture so I assumed that is the way to do that.

is there another way to do that?