On Saturday 03 February 2007 23:04, Matthias Urlichs wrote:
> Hi,
>
> Hans Verkuil:
> > #define VIDIOC_ENCODER_CMD _IORW('V', 69, struct
> > v4l2_encoder_cmd) #define VIDIOC_TRY_ENCODER_CMD _IORW('V', 69,
> > struct v4l2_encoder_cmd)
>
> These two are not supposed to be identical, I'd assume.
Obviously.
>
> > #define VIDIOC_DECODER_CMD _IORW('V', 69, struct
> > v4l2_decoder_cmd) #define VIDIOC_TRY_DECODER_CMD _IORW('V', 69,
> > struct v4l2_decoder_cmd)
>
> ... OK, make that four, depending on whether the sizes end up being
> identical.
I didn't bother with filling in the numbers, that's done when the API
becomes final.
> I'd also note that for hysteric raisins, the macro is named "_IOWR".
> (Trips me up every time, too.)
Ah, you're right.
> > STEP/REVERSE_STEP will step through the mpeg frame-by-frame.
>
> This may be a stupid question, but how does the application know what
> to write next, when you're reversing?
Typically (well, at least for the cx23415) the step reverses through the
current "Group Of Pictures" until the first picture is reached, then
the cards asks for the next (or in this case, previous) GOP. This
requires that the application is aware where in the program stream a
GOP starts and ends.
Hans
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