While I'm not very fond of "const", it's important for declarations
(it decides whether a symbol is emitted in a read-only or read/write
section). Fix all these cases, so we have writeable global data only
when we really need.
For some reason, we support writeable streams. (Only encoding uses that,
and the use of it looks messy enough that I want to replace it with FILE
or avio today.)
It's a chaos: most streams do not actually check the mode parameter like
they should. Simplify it, and let streams signal availability of write
mode by setting a flag in the stream info struct.
The way the url_options field was handled was not entirely sane: it's
actually a flexible array member, so it points to garbage for streams
which do not initialize this member (it just points to the data right
after the struct, which is garbage in theory and practice). This was
not actually a problem, since the field is only used if priv_size is
set (due to how this stuff is used). But it doesn't allow setting
priv_size only, which might be useful in some cases.
Also, make the protocols array not a fixed size array. Most stream
implementations have only 1 protocol prefix, but stream_lavf.c has
over 10 (whitelists ffmpeg protocols). The high size of the fixed
size protocol array wastes space, and it is _still_ annoying to
add new prefixes to stream_lavf (have to bump the maximum length),
so make it arbitrary length.
The two changes (plus some more cosmetic changes) arte conflated into
one, because it was annoying going over all the stream implementations.
Move the URL parsing code from m_option.c to stream.c, and simplify it
dramatically. This code originates from times when http code used this,
but now it's just relict from other stream implementations reusing this
code. Remove the unused bits and simplify the rest.
stream_vcd is insane, and the priv struct is different on every
platform, so drop the URL parsing. This means you can't specify a track
anymore, only the device. (Does anyone use stream_vcd? Not like this
couldn't be fixed, but it doesn't seem worth the effort, especially
because it'd require potentially touching platform specific code.)
These were printed only with -v. Most streams had them set to useless
or redundant values, so it's just badly maintained bloat.
Since we remove the "author" field too, and since this may have
copyright implications, we add the contents of the author fields to
the file headers, except if the name is already part of the file header.
This removes the dependency on DEMUXER_TYPE_* and the file_format
parameter from the stream open functions.
Remove some of the playlist handling code. It looks like this was
needed only for loading linked mov files with demux_mov (which was
removed long ago).
Delete a minor bit of dead network-related code from stream.c as well.
libavdevice supports various "special" video and audio inputs, such
as screen-capture or libavfilter filter graphs.
libavdevice inputs are implemented as demuxers. They don't use the
custom stream callbacks (in AVFormatContext.pb). Instead, input
parameters are passed as filename. This means the mpv stream layer has
to be disabled. Do this by adding the pseudo stream handler avdevice://,
whose only purpose is passing the filename to demux_lavf, without
actually doing anything.
Change the logic how the filename is passed to libavformat. Remove
handling of the filename from demux_open_lavf() and move it to
lavf_check_file(). (This also fixes a possible bug when skipping the
"lavf://" prefix.)
libavdevice now can be invoked by specifying demuxer and args as in:
mpv avdevice://demuxer:args
The args are passed as filename to libavformat. When using libavdevice
demuxers, their actual meaning is highly implementation specific. They
don't refer to actual filenames.
Note:
libavdevice is disabled by default. There is one problem: libavdevice
pulls in libavfilter, which in turn causes symbol clashes with mpv
internals. The problem is that libavfilter includes a mplayer filter
bridge, which is used to interface with a set of nearly unmodified
mplayer filters copied into libavfilter. This filter bridge uses the
same symbol names as mplayer/mpv's filter chain, which results in symbol
clashes at link-time.
This can be prevented by building ffmpeg with --disable-filter=mp, but
unfortunately this is not the default.
This means linking to libavdevice (which in turn forces linking with
libavfilter by default) must be disabled. We try doing this by compiling
a test file that defines one of the clashing symbols (vf_mpi_clear).
To enable libavdevice input, ffmpeg should be built with the options:
--disable-filter=mp
and mpv with:
--enable-libavdevice
Originally, I tried to auto-detect it. But the resulting complications
in configure did't seem worth the trouble.
