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authorwm4 <wm4@nowhere>2019-11-06 21:36:02 +0100
committerwm4 <wm4@nowhere>2019-11-06 21:36:02 +0100
commitf37f4de8496556afaa024e39e2efb433eb1680d4 (patch)
tree1ade8205598a3142d1fcbe5f32f461266ce81b76 /DOCS
parentabb089431d0467c3609207d0b27359ef08a6c16d (diff)
downloadmpv-f37f4de8496556afaa024e39e2efb433eb1680d4.tar.bz2
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stream: turn into a ring buffer, make size configurable
In some corner cases (see #6802), it can be beneficial to use a larger stream buffer size. Use this as argument to rewrite everything for no reason. Turn stream.c itself into a ring buffer, with configurable size. The latter would have been easily achievable with minimal changes, and the ring buffer is the hard part. There is no reason to have a ring buffer at all, except possibly if ffmpeg don't fix their awful mp4 demuxer, and some subtle issues with demux_mkv.c wanting to seek back by small offsets (the latter was handled with small stream_peek() calls, which are unneeded now). In addition, this turns small forward seeks into reads (where data is simply skipped). Before this commit, only stream_skip() did this (which also mean that stream_skip() simply calls stream_seek() now). Replace all stream_peek() calls with something else (usually stream_read_peek()). The function was a problem, because it returned a pointer to the internal buffer, which is now a ring buffer with wrapping. The new function just copies the data into a buffer, and in some cases requires callers to dynamically allocate memory. (The most common case, demux_lavf.c, required a separate buffer allocation anyway due to FFmpeg "idiosyncrasies".) This is the bulk of the demuxer_* changes. I'm not happy with this. There still isn't a good reason why there should be a ring buffer, that is complex, and most of the time just wastes half of the available memory. Maybe another rewrite soon. It also contains bugs; you're an alpha tester now.
Diffstat (limited to 'DOCS')
-rw-r--r--DOCS/man/options.rst26
1 files changed, 26 insertions, 0 deletions
diff --git a/DOCS/man/options.rst b/DOCS/man/options.rst
index 8dcbe1bcd8..3ae3264969 100644
--- a/DOCS/man/options.rst
+++ b/DOCS/man/options.rst
@@ -4196,6 +4196,32 @@ Cache
Currently, this is used for ``--cache-on-disk`` only.
+``--stream-buffer-size=<bytesize>``
+ Size of the low level stream byte buffer (default: 4KB). This is used as
+ buffer between demuxer and low level I/O (e.g. sockets). Generally, this
+ can be very small, and the main purpose is similar to the internal buffer
+ FILE in the C standard library will have.
+
+ Half of the buffer is always used for guaranteed seek back, which is
+ important for unseekable input.
+
+ There are known cases where this can help performance to set a large buffer:
+
+ 1. mp4 files. libavformat may trigger many small seeks in both
+ directions, depending on how the file was muxed.
+
+ 2. Certain network filesystems, which do not have a cache, and where
+ small reads can be inefficient.
+
+ In other cases, setting this to a large value can reduce performance.
+
+ Usually, read accesses are at half the buffer size, but it may happen that
+ accesses are done alternating with smaller and larger sizes (this is due to
+ the internal ring buffer wrap-around).
+
+ See ``--list-options`` for defaults and value range. ``<bytesize>`` options
+ accept suffixes such as ``KiB`` and ``MiB``.
+
Network
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