[FFmpeg-devel,v4,1/4] fftools/ffmpeg_filter: add -autoscale to disable/enable the default scale

diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
index cd35eb4..29da951 100644
--- a/doc/ffmpeg.texi
+++ b/doc/ffmpeg.texi
@@ -734,10 +734,6 @@  ffmpeg -dump_attachment:t "" -i INPUT
 Technical note -- attachments are implemented as codec extradata, so this
 option can actually be used to extract extradata from any stream, not just
 attachments.
-
-@item -noautorotate
-Disable automatically rotating video based on file metadata.
-
 @end table
 
 @section Video Options
@@ -819,6 +815,18 @@  Create the filtergraph specified by @var{filtergraph} and use it to
 filter the stream.
 
 This is an alias for @code{-filter:v}, see the @ref{filter_option,,-filter option}.
+
+@item -autorotate
+Automatically rotate the video according to file metadata. Enabled by
+default, use @option{-noautorotate} to disable it.
+
+@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 of filter graph might not be in the same resolution
+and may be inadequate for some encoder/muxer. Therefore, it is not recommended
+to disable it unless you really know what you are doing.
+Disable autoscale at your own risk.
 @end table
 
 @section Advanced Video options
diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
index 01f0410..5d52430 100644
--- a/fftools/ffmpeg.c
+++ b/fftools/ffmpeg.c
@@ -2133,6 +2133,7 @@  static int ifilter_send_frame(InputFilter *ifilter, AVFrame *frame)
 
     /* determine if the parameters for this input changed */
     need_reinit = ifilter->format != frame->format;
+    fg->autoscale = ifilter->ist->autoscale;
 
     switch (ifilter->ist->st->codecpar->codec_type) {
     case AVMEDIA_TYPE_AUDIO:
diff --git a/fftools/ffmpeg.h b/fftools/ffmpeg.h
index 7b6f802..1602406 100644
--- a/fftools/ffmpeg.h
+++ b/fftools/ffmpeg.h
@@ -133,6 +133,8 @@  typedef struct OptionsContext {
     int        nb_hwaccel_output_formats;
     SpecifierOpt *autorotate;
     int        nb_autorotate;
+    SpecifierOpt *autoscale;
+    int        nb_autoscale;
 
     /* output options */
     StreamMap *stream_maps;
@@ -285,6 +287,7 @@  typedef struct FilterGraph {
 
     AVFilterGraph *graph;
     int reconfiguration;
+    int autoscale;
 
     InputFilter   **inputs;
     int          nb_inputs;
@@ -335,6 +338,7 @@  typedef struct InputStream {
     int guess_layout_max;
 
     int autorotate;
+    int autoscale;
 
     int fix_sub_duration;
     struct { /* previous decoded subtitle and related variables */
diff --git a/fftools/ffmpeg_filter.c b/fftools/ffmpeg_filter.c
index 72838de..2a2eb08 100644
--- a/fftools/ffmpeg_filter.c
+++ b/fftools/ffmpeg_filter.c
@@ -469,7 +469,7 @@  static int configure_output_video_filter(FilterGraph *fg, OutputFilter *ofilter,
     if (ret < 0)
         return ret;
 
-    if (ofilter->width || ofilter->height) {
+    if ((ofilter->width || ofilter->height) && fg->autoscale) {
         char args[255];
         AVFilterContext *filter;
         AVDictionaryEntry *e = NULL;
diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
index f5ca18a..41cb676 100644
--- a/fftools/ffmpeg_opt.c
+++ b/fftools/ffmpeg_opt.c
@@ -742,7 +742,9 @@  static void add_input_streams(OptionsContext *o, AVFormatContext *ic)
         MATCH_PER_STREAM_OPT(ts_scale, dbl, ist->ts_scale, ic, st);
 
         ist->autorotate = 1;
+        ist->autoscale  = 1;
         MATCH_PER_STREAM_OPT(autorotate, i, ist->autorotate, ic, st);
+        MATCH_PER_STREAM_OPT(autoscale, i, ist->autoscale, ic, st);
 
         MATCH_PER_STREAM_OPT(codec_tags, str, codec_tag, ic, st);
         if (codec_tag) {
@@ -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."},
 
     /* audio options */
     { "aframes",        OPT_AUDIO | HAS_ARG  | OPT_PERFILE | OPT_OUTPUT,           { .func_arg = opt_audio_frames },