[FFmpeg-devel] libavcodec decoder output PIX_FMT

[Tomas Härdin]

Please avoid top-posting on this list.

On Mon, 2010-10-18 at 10:03 -0700, SD wrote:
> On Mon, Oct 18, 2010 at 12:14 AM, Tomas H?rdin <tomas.hardin at codemill.se>wrote:
> 
> > On Sat, 2010-10-16 at 12:40 -0700, Srinivasa Deevi wrote:
> > > Hi
> > >
> > > I would like to know if there are any restrictions on libavcodec decoder
> > > output to be anything other than YUV type. Can that be RGB24/32 format as
> > > well ?
> >
> > Yes. Almost all entries in the PixelFormat enum are ok (not sure about
> > the hwaccel ones). You can check out AVCodec::pix_fmts if you like, but
> > that's not always set. Also, the output pixel format will vary depending
> > on the input, even if using the same codec. For instance, DV can be
> > either 4:2:0, 4:1:1 or 4:2:2.
> >
> > > Also, if the decoder scales it down as well, how we inform the next level
> > > like libvo . Is this possible with ffmpeg ?
> >
> > The decoder shouldn't do any scaling. At least I haven't come across it
> > so far. It might request that the output should be cropped though, and
> > the resolution may change, thus requiring scaling.
> >
> > The answer to both of these questions is probably to always inspect
> > pix_fmt, width/height, coded_width/coded_height etc. and act
> > accordingly.
> >
> > For specific codecs it might be possible to guarantee that for instance
> > resolution doesn't change, but not in the general case.
> >
> > /Tomas
> >
> >
> Tomas,
> 
> Thank you for your reply.
> 
> I have one more question. App -> parser -> decoder -> VO -> framebuffer
> 
> Is the above possible ? Can we implement in above format ? How can we bypass
> any in between decoder and VO if possible.

I doubt you can bypass the decoder. Unless you have raw video of course.

> or App -> parser -> decoder -> libswscale -> VO -> framebuffer
> if the only way we should implement ?

If you can write to the frame buffer directly and its pixel format and resolution matches that of the decoder then should be able to pass it to the decode function. Just set up the AVFrame struct properly.

> >>The answer to both of these questions is probably to always inspect
> pix_fmt, width/height, coded_width/coded_height etc. and act
> accordingly
> 
> Is not the above based on the decoder that we choose  ?

That is correct. The lavc decoders will/should never output any pixel format or resolution that is not supported by that codec's specs. At least I haven't come across any that do yet.

Also, if your video comes from some kind of device then that might also have certain guarantees regarding the frame format. Think of a camera that always outputs the same resolution for instance.

/Tomas
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