fftools/ffmpeg_filter: add -autoscale to disable/enable the default scale

Currently, ffmpeg inserts scale filter by default in the filter graph
to force the whole decoded stream to scale into the same size with the
first frame. It's not quite make sense in resolution changing cases if
user wants the rawvideo without any scale.

Using autoscale/noautoscale as an output option to indicate whether auto
inserting the scale filter in the filter graph:
    -noautoscale or -autoscale 0:
    disable the default auto scale filter inserting.

ffmpeg -y -i input.mp4 out1.yuv -noautoscale out2.yuv -autoscale 0 out3.yuv

Update docs.

Suggested-by:  Mark Thompson <sw@jkqxz.net>
Reviewed-by:   Nicolas George <george@nsup.org>
Signed-off-by: U. Artie Eoff <ullysses.a.eoff@intel.com>
Signed-off-by: Linjie Fu <linjie.fu@intel.com>

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

fftools/ffmpeg.h

@@ -229,6 +229,8 @@ typedef struct OptionsContext {
     int        nb_time_bases;
     SpecifierOpt *enc_time_bases;
     int        nb_enc_time_bases;
+    SpecifierOpt *autoscale;
+    int        nb_autoscale;
 } OptionsContext;
 
 typedef struct InputFilter {
@@ -479,6 +481,7 @@ typedef struct OutputStream {
     int force_fps;
     int top_field_first;
     int rotate_overridden;
+    int autoscale;
     double rotate_override_value;
 
     AVRational frame_aspect_ratio;

fftools/ffmpeg_filter.c

@@ -470,7 +470,7 @@ 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) && ofilter->ost->autoscale) {
         char args[255];
         AVFilterContext *filter;
         AVDictionaryEntry *e = NULL;

fftools/ffmpeg_opt.c

@@ -62,6 +62,7 @@ static const char *opt_name_hwaccels[]                  = {"hwaccel", NULL};
 static const char *opt_name_hwaccel_devices[]           = {"hwaccel_device", NULL};
 static const char *opt_name_hwaccel_output_formats[]    = {"hwaccel_output_format", NULL};
 static const char *opt_name_autorotate[]                = {"autorotate", NULL};
+static const char *opt_name_autoscale[]                 = {"autoscale", NULL};
 static const char *opt_name_max_frames[]                = {"frames", "aframes", "vframes", "dframes", NULL};
 static const char *opt_name_bitstream_filters[]         = {"bsf", "absf", "vbsf", NULL};
 static const char *opt_name_codec_tags[]                = {"tag", "atag", "vtag", "stag", NULL};
@@ -1462,6 +1463,8 @@ static OutputStream *new_output_stream(OptionsContext *o, AVFormatContext *oc, e
         ost->encoder_opts  = filter_codec_opts(o->g->codec_opts, ost->enc->id, oc, st, ost->enc);
 
         MATCH_PER_STREAM_OPT(presets, str, preset, oc, st);
+        ost->autoscale = 1;
+        MATCH_PER_STREAM_OPT(autoscale, i, ost->autoscale, oc, st);
         if (preset && (!(ret = get_preset_file_2(preset, ost->enc->name, &s)))) {
             do  {
                 buf = get_line(s);
@@ -3664,6 +3667,9 @@ 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_OUTPUT,                               { .off = OFFSET(autoscale) },
+        "automatically insert a scale filter at the end of the filter graph" },
 
     /* audio options */
     { "aframes",        OPT_AUDIO | HAS_ARG  | OPT_PERFILE | OPT_OUTPUT,           { .func_arg = opt_audio_frames },