[gst-devel] [gst-embedded] gstreamer dma buffer & management

[Marco Ballesio]

Hi,

yes, I DO hate the default gmail settings..

---------- Forwarded message ----------
From: Marco Ballesio <gibrovacco at gmail.com>
Date: Sat, Sep 18, 2010 at 4:52 PM
Subject: Re: [gst-embedded] gstreamer dma buffer & management
To: Feng Ye <fye at broadcom.com>


Hi,

On Fri, Sep 17, 2010 at 2:49 AM, Feng Ye <fye at broadcom.com> wrote:

> Hello there,
>
> I am working on a video dec plugin (based on hardware dec). I plan to use
> filesrc to read a raw H264 file and feed to my plugin.
>

it's generically better to use a container format rather than a raw h264
byte-stream. If a container is not an option for your case, maybe you could
use at least an annex-B compliant stream. This makes it easier to identify
NAL boundaries. It should anyway possible to use even an unformatted NAL
sequence (see below).


> The buffers from plugin's sink pad are the source data for decoding so they
> need to be DMA-able. Is there way to control how the buffers are allocated?
> Since they are allocated in filesrc so that's not possible? Looks like I
> will need to allocate my own buffer in my plugin and then copy them over?
>

if you're not using any container format, the source has no way to pass to
you buffers aligned with NAL boundaries, so you definitely need an adapter
somewhere (see below).


>
> Also, a video frame may contain less bytes than what's in the buffer, what
> do I do with the remaining bytes?
> >From the ffmpeg example (they are software based so the first dma question
> does not exist), they create a sub buffer of the remaining bytes and then
> does a buffer join. These are time consuming I think.


yes it is, but I guess you could afford it for compressed data. The overhead
depends, of course, on the bandwidth you're using.


> I wonder if there are other faster solution? One thing I think might help
> is to have another plugin in between, which parse the file and only give one
> frame size of data to my plugin. But I am not sure if these kind of plugin
> exists.
>

You can use h264parse for this. It will identify NAL boundaries and pass
them to your plugin on separated buffers. Btw everything has a price and in
this case it's the penalty like described some rows above.

Regards.


>
>
> Thanks,
> Feng
>
>
>
>
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