AVFormatContext: add metadata_header_padding field

This field is used to store the number of bytes that should be written
as padding to a metadata header of a file.  For example:
 - The FLAC format's METADATA_BLOCK_PADDING [1]
 - The ID3v2 tag format's padding           [2]

[1] http://xiph.org/flac/format.html#metadata_block_padding
[2] http://id3.org/id3v2.3.0#ID3v2_overviewSigned-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/avformat.h

@@ -1348,6 +1348,13 @@ typedef struct AVFormatContext {
      * Demuxing: Set by user via av_format_set_subtitle_codec (NO direct access).
      */
     AVCodec *subtitle_codec;
+
+    /**
+     * Number of bytes to be written as padding in a metadata header.
+     * Demuxing: Unused.
+     * Muxing: Set by user via av_format_set_metadata_header_padding.
+     */
+    int metadata_header_padding;
 } AVFormatContext;
 
 int av_format_get_probe_score(const AVFormatContext *s);
@@ -1357,6 +1364,8 @@ AVCodec * av_format_get_audio_codec(const AVFormatContext *s);
 void      av_format_set_audio_codec(AVFormatContext *s, AVCodec *c);
 AVCodec * av_format_get_subtitle_codec(const AVFormatContext *s);
 void      av_format_set_subtitle_codec(AVFormatContext *s, AVCodec *c);
+int       av_format_get_metadata_header_padding(const AVFormatContext *s);
+void      av_format_set_metadata_header_padding(AVFormatContext *s, int c);
 
 /**
  * Returns the method used to set ctx->duration.

libavformat/options_table.h

@@ -77,6 +77,7 @@ static const AVOption avformat_options[] = {
 {"skip_initial_bytes", "set number of bytes to skip before reading header and frames", OFFSET(skip_initial_bytes), AV_OPT_TYPE_INT, {.i64 = 0}, 0, INT_MAX-1, D},
 {"correct_ts_overflow", "correct single timestamp overflows", OFFSET(correct_ts_overflow), AV_OPT_TYPE_INT, {.i64 = 1}, 0, 1, D},
 {"flush_packets", "enable flushing of the I/O context after each packet", OFFSET(flush_packets), AV_OPT_TYPE_INT, {.i64 = 1}, 0, 1, E},
+{"metadata_header_padding", "set number of bytes to be written as padding in a metadata header", OFFSET(metadata_header_padding), AV_OPT_TYPE_INT, {.i64 = -1}, -1, INT_MAX, E},
 {NULL},
 };
 

libavformat/utils.c

@@ -103,6 +103,7 @@ MAKE_ACCESSORS(AVStream, stream, AVRational, r_frame_rate)
 MAKE_ACCESSORS(AVFormatContext, format, AVCodec *, video_codec)
 MAKE_ACCESSORS(AVFormatContext, format, AVCodec *, audio_codec)
 MAKE_ACCESSORS(AVFormatContext, format, AVCodec *, subtitle_codec)
+MAKE_ACCESSORS(AVFormatContext, format, int, metadata_header_padding)
 
 static AVCodec *find_decoder(AVFormatContext *s, AVStream *st, enum AVCodecID codec_id)
 {

libavformat/version.h

@@ -30,8 +30,8 @@
 #include "libavutil/version.h"
 
 #define LIBAVFORMAT_VERSION_MAJOR 55
-#define LIBAVFORMAT_VERSION_MINOR 25
-#define LIBAVFORMAT_VERSION_MICRO 101
+#define LIBAVFORMAT_VERSION_MINOR 26
+#define LIBAVFORMAT_VERSION_MICRO 100
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \