The framework will allocate a buffer and copy the data to it,
that takes time. But it avoids constently creating and
destroyng the shared memory segment, and that saves more time.
On my setup,
from ~200 to ~300 FPS at full screen (1920×1200),
from ~1400 to ~3300 at smaller size (640×480),
similar to legacy x11grab and confirmed by others.
Plus, shared memory segments are a scarce resource,
allocating potentially many is a bad idea.
Note: if the application were to drop all references to the
buffer before the next call to av_read_frame(), then passing
the shared memory segment as a refcounted buffer would be
even more efficient, but it is hard to guarantee, and it does
not happen with the ffmpeg command-line tool. Using a small
number of preallocated buffers and resorting to a copy when
the pool is exhausted would be a solution to get the better
of both worlds.
Currently, AVStream contains an embedded AVCodecContext instance, which
is used by demuxers to export stream parameters to the caller and by
muxers to receive stream parameters from the caller. It is also used
internally as the codec context that is passed to parsers.
In addition, it is also widely used by the callers as the decoding (when
demuxer) or encoding (when muxing) context, though this has been
officially discouraged since Libav 11.
There are multiple important problems with this approach:
- the fields in AVCodecContext are in general one of
* stream parameters
* codec options
* codec state
However, it's not clear which ones are which. It is consequently
unclear which fields are a demuxer allowed to set or a muxer allowed to
read. This leads to erratic behaviour depending on whether decoding or
encoding is being performed or not (and whether it uses the AVStream
embedded codec context).
- various synchronization issues arising from the fact that the same
context is used by several different APIs (muxers/demuxers,
parsers, bitstream filters and encoders/decoders) simultaneously, with
there being no clear rules for who can modify what and the different
processes being typically delayed with respect to each other.
- avformat_find_stream_info() making it necessary to support opening
and closing a single codec context multiple times, thus
complicating the semantics of freeing various allocated objects in the
codec context.
Those problems are resolved by replacing the AVStream embedded codec
context with a newly added AVCodecParameters instance, which stores only
the stream parameters exported by the demuxers or read by the muxers.
Incidentally `-y` also collides with avconv global options.
Update x11grab to match and document the option.
CC: libav-stable@libav.org
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
The feature is implemented using a transparent window and drawing
inside it a rectangle filling the whole window to highlight it.
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
Fixes trac ticket #4164
This is to address an error when using show_region, which would cause part of the captured area to become static.
It looks like the rectangle specifying the capture area was relative to the capture window.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Old versions of libxcb do not provide xcb_shape_rectangles().
The issue can be fixed differently but this small change fixes
some fate platforms and a user reported compilation problem.
Reported and tested by trac user kevmitch.
Fixes ticket #4067.
Diego Biurrun
Nicolas George
Anton Khirnov
Ganesh Ajjanagadde
Vittorio Giovara
Luca Barbato
Daniel Moran
Michael Niedermayer
Carl Eugen Hoyos
Boris Reisig