[FFmpeg-devel] [PATCH] fftools/ffmpeg_filter: add -autoscale to disable/enable the default scale

[Linjie Fu]

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 to indicate whether auto inserting the scale
filter in the filter graph:
    -noautoscale or -autoscale 0:
    disable the default auto scale filter inserting.

Update docs.

Signed-off-by: U. Artie Eoff <ullysses.a.eoff at intel.com>
Signed-off-by: Linjie Fu <linjie.fu at intel.com>
---
 doc/ffmpeg.texi         | 16 ++++++++++++----
 fftools/ffmpeg.c        |  1 +
 fftools/ffmpeg.h        |  4 ++++
 fftools/ffmpeg_filter.c |  2 +-
 fftools/ffmpeg_opt.c    |  8 ++++++++
 5 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
index dd461c0..716dd2c 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.
-
- at 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}.
+
+ at item -autorotate
+Automatically rotate the video according to file metadata. Enabled by
+default, use @option{-noautorotate} to disable it.
+
+ at 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 6bcd7b9..864c1fb 100644
--- a/fftools/ffmpeg.c
+++ b/fftools/ffmpeg.c
@@ -2125,6 +2125,7 @@ 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 40cc4c1..dafcab7 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 1510e02..37083f2 100644
--- a/fftools/ffmpeg_opt.c
+++ b/fftools/ffmpeg_opt.c
@@ -743,7 +743,9 @@ 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) {
@@ -3650,6 +3652,12 @@ 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 },
-- 
2.7.4