ffprobe: add option to control optional fields display

doc/ffprobe.texi

@@ -335,6 +335,12 @@ Show information about all pixel formats supported by FFmpeg.
 Pixel format information for each format is printed within a section
 with name "PIXEL_FORMAT".
 
+@item -show_optional_fields @var{value}
+Some writers viz. JSON and XML, omit the printing of fields with invalid or non-applicable values,
+while other writers always print them. This option enables one to control this behaviour.
+Valid values are @code{always}/@code{1}, @code{never}/@code{0} and @code{auto}/@code{-1}.
+Default is @var{auto}.
+
 @item -bitexact
 Force bitexact output, useful to produce output which is not dependent
 on the specific build.

fftools/ffprobe.c

@@ -117,6 +117,11 @@ static int use_byte_value_binary_prefix = 0;
 static int use_value_sexagesimal_format = 0;
 static int show_private_data            = 1;
 
+#define SHOW_OPTIONAL_FIELDS_AUTO       -1
+#define SHOW_OPTIONAL_FIELDS_NEVER       0
+#define SHOW_OPTIONAL_FIELDS_ALWAYS      1
+static int show_optional_fields = SHOW_OPTIONAL_FIELDS_AUTO;
+
 static char *print_format;
 static char *stream_specifier;
 static char *show_data_hash;
@@ -745,8 +750,10 @@ static inline int writer_print_string(WriterContext *wctx,
     const struct section *section = wctx->section[wctx->level];
     int ret = 0;
 
-    if ((flags & PRINT_STRING_OPT)
-        && !(wctx->writer->flags & WRITER_FLAG_DISPLAY_OPTIONAL_FIELDS))
+    if (show_optional_fields == SHOW_OPTIONAL_FIELDS_NEVER ||
+        (show_optional_fields == SHOW_OPTIONAL_FIELDS_AUTO
+        && (flags & PRINT_STRING_OPT)
+        && !(wctx->writer->flags & WRITER_FLAG_DISPLAY_OPTIONAL_FIELDS)))
         return 0;
 
     if (section->show_all_entries || av_dict_get(section->entries_to_show, key, NULL, 0)) {
@@ -3244,6 +3251,17 @@ static void ffprobe_show_pixel_formats(WriterContext *w)
     writer_print_section_footer(w);
 }
 
+static int opt_show_optional_fields(void *optctx, const char *opt, const char *arg)
+{
+    if      (!av_strcasecmp(arg, "always")) show_optional_fields = SHOW_OPTIONAL_FIELDS_ALWAYS;
+    else if (!av_strcasecmp(arg, "never"))  show_optional_fields = SHOW_OPTIONAL_FIELDS_NEVER;
+    else if (!av_strcasecmp(arg, "auto"))   show_optional_fields = SHOW_OPTIONAL_FIELDS_AUTO;
+
+    if (show_optional_fields == SHOW_OPTIONAL_FIELDS_AUTO && av_strcasecmp(arg, "auto"))
+        show_optional_fields = parse_number_or_die("show_optional_fields", arg, OPT_INT, SHOW_OPTIONAL_FIELDS_AUTO, SHOW_OPTIONAL_FIELDS_ALWAYS);
+    return 0;
+}
+
 static int opt_format(void *optctx, const char *opt, const char *arg)
 {
     iformat = av_find_input_format(arg);
@@ -3631,6 +3649,7 @@ static const OptionDef real_options[] = {
     { "show_library_versions", 0, { .func_arg = &opt_show_library_versions }, "show library versions" },
     { "show_versions",         0, { .func_arg = &opt_show_versions }, "show program and library versions" },
     { "show_pixel_formats", 0, { .func_arg = &opt_show_pixel_formats }, "show pixel format descriptions" },
+    { "show_optional_fields", HAS_ARG, { .func_arg = &opt_show_optional_fields }, "show optional fields" },
     { "show_private_data", OPT_BOOL, { &show_private_data }, "show private data" },
     { "private",           OPT_BOOL, { &show_private_data }, "same as show_private_data" },
     { "bitexact", OPT_BOOL, {&do_bitexact}, "force bitexact output" },