On 22-07-2019 01:40 PM, Fu, Linjie wrote:
-----Original Message-----
From: ffmpeg-devel [mailto:ffmpeg-devel-boun...@ffmpeg.org] On Behalf
Of Gyan
Sent: Saturday, July 20, 2019 13:29
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH, v3] fftools/ffmpeg_filter: add -
autoscale to disable/enable the default scale
diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
index cd35eb49c8..99121b6981 100644
--- a/doc/ffmpeg.texi
+++ b/doc/ffmpeg.texi
+@item -autoscale
+Automatically scale the video according to the resolution of first frame.
+Enabled by default, use @option{-noautoscale} to disable it. When
autoscale is
+disabled, all output frames might not be in the same resolution and may
require
+some additional explicit processing according to your final
rendering/output
+destination. Disabling autoscale may not work in all situations. Therefore,
it
+is not recommended to disable it unless you really know what you are
doing.
+Disable autoscale at your own risk.
Since the auto scaling happens at the end of the graph, what may the
"additional explicit processing" be?
Vpp processing may not be influenced, a warning in transcode is needed.
The expression seems to be improper, how about:
"When autoscale is disabled, all output frames of filter graph might not be in
the same
resolution and may be inadequate for encoder/muxer."
or other suggestions?
@@ -3640,6 +3642,12 @@ const OptionDef options[] = {
{ "autorotate", HAS_ARG | OPT_BOOL | OPT_SPEC |
OPT_EXPERT | OPT_INPUT,
{ .off =
OFFSET(autorotate) },
"automatically insert correct rotate filters" },
+ { "autoscale", HAS_ARG | OPT_BOOL | OPT_SPEC |
+ OPT_EXPERT | OPT_INPUT,
{ .off =
OFFSET(autoscale) },
+ "automatically insert a scale filter at the end of the filter graph if
a
resolution"
+ "change is detected. This ensures all frames are the same resolution
as the first frame"
+ "when they leave the filter chain (this option is enabled by default)."
+ "If disabled, some encoders/muxers may not support this mode."},
Which muxers can detect or check for prop changes within coded
bitstreams? Which encoders are known to be able to handle
changing resolution?
It's not supported currently (even in libvpx-vp9, since vp9 supports dynamic
resolution in spec).
I don't intend to be so absolutely in doc, will it be better for you to modify
like:
"If disabled, encoders/muxers won't support this mode currently."
So other than `-c:v rawvideo -f rawvideo`, there is no combination
that supports changing frame sizes?
Gyan
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