@@ -16,6 +16,7 @@ version 10:

 - new trim and atrim filters

 - avconv -t and -ss (output-only) options are now sample-accurate when

   transcoding audio

+- Matroska muxer can now put the index at the beginning of the file.

 version 9:

@@ -373,6 +373,27 @@ For example a 3D WebM clip can be created using the following command line:

 avconv -i sample_left_right_clip.mpg -an -c:v libvpx -metadata STEREO_MODE=left_right -y stereo_clip.webm

 @end example

+This muxer supports the following options:

+

+@table @option

+

+@item reserve_index_space

+By default, this muxer writes the index for seeking (called cues in Matroska

+terms) at the end of the file, because it cannot know in advance how much space

+to leave for the index at the beginning of the file. However for some use cases

+-- e.g.  streaming where seeking is possible but slow -- it is useful to put the

+index at the beginning of the file.

+

+If this option is set to a non-zero value, the muxer will reserve a given amount

+of space in the file header and then try to write the cues there when the muxing

+finishes. If the available space does not suffice, muxing will fail. A safe size

+for most use cases should be about 50kB per hour of video.

+

+Note that cues are only written if the output is seekable and this option will

+have no effect if it is not.

+

+@end table

+

 @section segment

 Basic stream segmenter.

@@ -34,6 +34,7 @@

 #include "libavutil/intreadwrite.h"

 #include "libavutil/lfg.h"

 #include "libavutil/mathematics.h"

+#include "libavutil/opt.h"

 #include "libavutil/random_seed.h"

 #include "libavutil/samplefmt.h"

@@ -79,6 +80,7 @@ typedef struct {

 #define MODE_WEBM       0x02

 typedef struct MatroskaMuxContext {

+    const AVClass  *class;

     int             mode;

     AVIOContext   *dyn_bc;

     ebml_master     segment;

@@ -95,6 +97,9 @@ typedef struct MatroskaMuxContext {

     AVPacket        cur_audio_pkt;

     int have_attachments;

+

+    int reserve_cues_space;

+    int64_t cues_pos;

 } MatroskaMuxContext;

@@ -968,6 +973,11 @@ static int mkv_write_header(AVFormatContext *s)

     if (mkv->cues == NULL)

         return AVERROR(ENOMEM);

+    if (pb->seekable && mkv->reserve_cues_space) {

+        mkv->cues_pos = avio_tell(pb);

+        put_ebml_void(pb, mkv->reserve_cues_space);

+    }

+

     av_init_packet(&mkv->cur_audio_pkt);

     mkv->cur_audio_pkt.size = 0;

@@ -1250,7 +1260,28 @@ static int mkv_write_trailer(AVFormatContext *s)

     if (pb->seekable) {

         if (mkv->cues->num_entries) {

-            cuespos = mkv_write_cues(pb, mkv->cues, s->nb_streams);

+            if (mkv->reserve_cues_space) {

+                int64_t cues_end;

+

+                currentpos = avio_tell(pb);

+                avio_seek(pb, mkv->cues_pos, SEEK_SET);

+

+                cuespos = mkv_write_cues(pb, mkv->cues, s->nb_streams);

+                cues_end = avio_tell(pb);

+                if (cues_end > cuespos + mkv->reserve_cues_space) {

+                    av_log(s, AV_LOG_ERROR, "Insufficient space reserved for cues: %d "

+                           "(needed: %"PRId64").\n", mkv->reserve_cues_space,

+                           cues_end - cuespos);

+                    return AVERROR(EINVAL);

+                }

+

+                if (cues_end < cuespos + mkv->reserve_cues_space)

+                    put_ebml_void(pb, mkv->reserve_cues_space - (cues_end - cuespos));

+

+                avio_seek(pb, currentpos, SEEK_SET);

+            } else {

+                cuespos = mkv_write_cues(pb, mkv->cues, s->nb_streams);

+            }

             ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_CUES, cuespos);

             if (ret < 0) return ret;

@@ -1291,7 +1322,22 @@ static int mkv_query_codec(enum AVCodecID codec_id, int std_compliance)

     return 0;

 }

+#define OFFSET(x) offsetof(MatroskaMuxContext, x)

+#define FLAGS AV_OPT_FLAG_ENCODING_PARAM

+static const AVOption options[] = {

+    { "reserve_index_space", "Reserve a given amount of space (in bytes) at the beginning "

+        "of the file for the index (cues).", OFFSET(reserve_cues_space), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, FLAGS },

+    { NULL },

+};

+

 #if CONFIG_MATROSKA_MUXER

+static const AVClass matroska_class = {

+    .class_name = "matroska muxer",

+    .item_name  = av_default_item_name,

+    .option     = options,

+    .version    = LIBAVUTIL_VERSION_INT,

+};

+

 AVOutputFormat ff_matroska_muxer = {

     .name              = "matroska",

     .long_name         = NULL_IF_CONFIG_SMALL("Matroska"),

@@ -1312,10 +1358,18 @@ AVOutputFormat ff_matroska_muxer = {

     },

     .subtitle_codec    = AV_CODEC_ID_SSA,

     .query_codec       = mkv_query_codec,

+    .priv_class        = &matroska_class,

 };

 #endif

 #if CONFIG_WEBM_MUXER

+static const AVClass webm_class = {

+    .class_name = "webm muxer",

+    .item_name  = av_default_item_name,

+    .option     = options,

+    .version    = LIBAVUTIL_VERSION_INT,

+};

+

 AVOutputFormat ff_webm_muxer = {

     .name              = "webm",

     .long_name         = NULL_IF_CONFIG_SMALL("WebM"),

@@ -1329,10 +1383,17 @@ AVOutputFormat ff_webm_muxer = {

     .write_trailer     = mkv_write_trailer,

     .flags             = AVFMT_GLOBALHEADER | AVFMT_VARIABLE_FPS |

                          AVFMT_TS_NONSTRICT,

+    .priv_class        = &webm_class,

 };

 #endif

 #if CONFIG_MATROSKA_AUDIO_MUXER

+static const AVClass mka_class = {

+    .class_name = "matroska audio muxer",

+    .item_name  = av_default_item_name,

+    .option     = options,

+    .version    = LIBAVUTIL_VERSION_INT,

+};

 AVOutputFormat ff_matroska_audio_muxer = {

     .name              = "matroska",

     .long_name         = NULL_IF_CONFIG_SMALL("Matroska"),

@@ -1347,5 +1408,6 @@ AVOutputFormat ff_matroska_audio_muxer = {

     .write_trailer     = mkv_write_trailer,

     .flags             = AVFMT_GLOBALHEADER | AVFMT_TS_NONSTRICT,

     .codec_tag         = (const AVCodecTag* const []){ ff_codec_wav_tags, 0 },

+    .priv_class        = &mka_class,

 };

 #endif

@@ -31,7 +31,7 @@

 #define LIBAVFORMAT_VERSION_MAJOR 55

 #define LIBAVFORMAT_VERSION_MINOR  0

-#define LIBAVFORMAT_VERSION_MICRO  0

+#define LIBAVFORMAT_VERSION_MICRO  1

 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \

                                                LIBAVFORMAT_VERSION_MINOR, \