avcodec: export motion vectors in frame side data on demand

The reasoning behind this addition is that various third party
applications are interested in getting some motion information out of a
video "for free" when it is available.

It was considered to export other information as well (such as the intra
information about the block, or the quantization) but the structure
might have ended up into a half full-generic, half full of codec
specific cruft. If more information is necessary, it should either be
added in the "flags" field of the AVMotionVector structure, or in
another side-data.

This commit also includes an example exporting them in a CSV stream.

5 files changed, 193 insertions, 0 deletions

diff --git a/doc/APIchanges b/doc/APIchanges
index 8b3051c255..1bed10778d 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -15,6 +15,9 @@ libavutil:     2014-08-09
 
 API changes, most recent first:
 
+2014-08-xx - xxxxxxx - lavu 54.5.100 - frame.h motion_vector.h
+  Add AV_FRAME_DATA_MOTION_VECTORS side data and AVMotionVector structure
+
 2014-08-16 - xxxxxxx - lswr 1.1.100 - swresample.h
   Add AVFrame based API
 
diff --git a/doc/Makefile b/doc/Makefile
index 99f588ac05..2fb9058e6a 100644
--- a/doc/Makefile
+++ b/doc/Makefile
@@ -39,6 +39,7 @@ DOCS = $(DOCS-yes)
 DOC_EXAMPLES-$(CONFIG_AVIO_READING_EXAMPLE)      += avio_reading
 DOC_EXAMPLES-$(CONFIG_AVCODEC_EXAMPLE)           += avcodec
 DOC_EXAMPLES-$(CONFIG_DEMUXING_DECODING_EXAMPLE) += demuxing_decoding
+DOC_EXAMPLES-$(CONFIG_EXTRACT_MVS_EXAMPLE)       += extract_mvs
 DOC_EXAMPLES-$(CONFIG_FILTER_AUDIO_EXAMPLE)      += filter_audio
 DOC_EXAMPLES-$(CONFIG_FILTERING_AUDIO_EXAMPLE)   += filtering_audio
 DOC_EXAMPLES-$(CONFIG_FILTERING_VIDEO_EXAMPLE)   += filtering_video
diff --git a/doc/codecs.texi b/doc/codecs.texi
index 1160e5d800..820dce51e6 100644
--- a/doc/codecs.texi
+++ b/doc/codecs.texi
@@ -797,6 +797,9 @@ Frame data might be split into multiple chunks.
 Show all frames before the first keyframe.
 @item skiprd
 Deprecated, use mpegvideo private options instead.
+@item export_mvs
+Export motion vectors into frame side-data (see @code{AV_FRAME_DATA_MOTION_VECTORS})
+for codecs that support it. See also @file{doc/examples/export_mvs.c}.
 @end table
 
 @item error @var{integer} (@emph{encoding,video})
diff --git a/doc/examples/Makefile b/doc/examples/Makefile
index 03c7021e8b..07251fe3c2 100644
--- a/doc/examples/Makefile
+++ b/doc/examples/Makefile
@@ -14,6 +14,7 @@ LDLIBS := $(shell pkg-config --libs $(FFMPEG_LIBS)) $(LDLIBS)
 EXAMPLES=       avio_reading                       \
                 decoding_encoding                  \
                 demuxing_decoding                  \
+                extract_mvs                        \
                 filtering_video                    \
                 filtering_audio                    \
                 metadata                           \
diff --git a/doc/examples/extract_mvs.c b/doc/examples/extract_mvs.c
new file mode 100644
index 0000000000..d6fd61335e
--- /dev/null
+++ b/doc/examples/extract_mvs.c
@@ -0,0 +1,185 @@
+/*
+ * Copyright (c) 2012 Stefano Sabatini
+ * Copyright (c) 2014 Clément Bœsch
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <libavutil/motion_vector.h>
+#include <libavformat/avformat.h>
+
+static AVFormatContext *fmt_ctx = NULL;
+static AVCodecContext *video_dec_ctx = NULL;
+static AVStream *video_stream = NULL;
+static const char *src_filename = NULL;
+
+static int video_stream_idx = -1;
+static AVFrame *frame = NULL;
+static AVPacket pkt;
+static int video_frame_count = 0;
+
+static int decode_packet(int *got_frame, int cached)
+{
+    int decoded = pkt.size;
+
+    *got_frame = 0;
+
+    if (pkt.stream_index == video_stream_idx) {
+        int ret = avcodec_decode_video2(video_dec_ctx, frame, got_frame, &pkt);
+        if (ret < 0) {
+            fprintf(stderr, "Error decoding video frame (%s)\n", av_err2str(ret));
+            return ret;
+        }
+
+        if (*got_frame) {
+            int i;
+            AVFrameSideData *sd;
+
+            video_frame_count++;
+            sd = av_frame_get_side_data(frame, AV_FRAME_DATA_MOTION_VECTORS);
+            if (sd) {
+                const AVMotionVector *mvs = (const AVMotionVector *)sd->data;
+                for (i = 0; i < sd->size / sizeof(*mvs); i++) {
+                    const AVMotionVector *mv = &mvs[i];
+                    printf("%d,%2d,%2d,%2d,%4d,%4d,%4d,%4d,0x%"PRIx64"\n",
+                           video_frame_count, mv->source,
+                           mv->w, mv->h, mv->src_x, mv->src_y,
+                           mv->dst_x, mv->dst_y, mv->flags);
+                }
+            }
+        }
+    }
+
+    return decoded;
+}
+
+static int open_codec_context(int *stream_idx,
+                              AVFormatContext *fmt_ctx, enum AVMediaType type)
+{
+    int ret;
+    AVStream *st;
+    AVCodecContext *dec_ctx = NULL;
+    AVCodec *dec = NULL;
+    AVDictionary *opts = NULL;
+
+    ret = av_find_best_stream(fmt_ctx, type, -1, -1, NULL, 0);
+    if (ret < 0) {
+        fprintf(stderr, "Could not find %s stream in input file '%s'\n",
+                av_get_media_type_string(type), src_filename);
+        return ret;
+    } else {
+        *stream_idx = ret;
+        st = fmt_ctx->streams[*stream_idx];
+
+        /* find decoder for the stream */
+        dec_ctx = st->codec;
+        dec = avcodec_find_decoder(dec_ctx->codec_id);
+        if (!dec) {
+            fprintf(stderr, "Failed to find %s codec\n",
+                    av_get_media_type_string(type));
+            return AVERROR(EINVAL);
+        }
+
+        /* Init the video decoder */
+        av_dict_set(&opts, "flags2", "+export_mvs", 0);
+        if ((ret = avcodec_open2(dec_ctx, dec, &opts)) < 0) {
+            fprintf(stderr, "Failed to open %s codec\n",
+                    av_get_media_type_string(type));
+            return ret;
+        }
+    }
+
+    return 0;
+}
+
+int main(int argc, char **argv)
+{
+    int ret = 0, got_frame;
+
+    if (argc != 2) {
+        fprintf(stderr, "Usage: %s <video>\n", argv[0]);
+        exit(1);
+    }
+    src_filename = argv[1];
+
+    av_register_all();
+
+    if (avformat_open_input(&fmt_ctx, src_filename, NULL, NULL) < 0) {
+        fprintf(stderr, "Could not open source file %s\n", src_filename);
+        exit(1);
+    }
+
+    if (avformat_find_stream_info(fmt_ctx, NULL) < 0) {
+        fprintf(stderr, "Could not find stream information\n");
+        exit(1);
+    }
+
+    if (open_codec_context(&video_stream_idx, fmt_ctx, AVMEDIA_TYPE_VIDEO) >= 0) {
+        video_stream = fmt_ctx->streams[video_stream_idx];
+        video_dec_ctx = video_stream->codec;
+    }
+
+    av_dump_format(fmt_ctx, 0, src_filename, 0);
+
+    if (!video_stream) {
+        fprintf(stderr, "Could not find video stream in the input, aborting\n");
+        ret = 1;
+        goto end;
+    }
+
+    frame = av_frame_alloc();
+    if (!frame) {
+        fprintf(stderr, "Could not allocate frame\n");
+        ret = AVERROR(ENOMEM);
+        goto end;
+    }
+
+    printf("framenum,source,blockw,blockh,srcx,srcy,dstx,dsty,flags\n");
+
+    /* initialize packet, set data to NULL, let the demuxer fill it */
+    av_init_packet(&pkt);
+    pkt.data = NULL;
+    pkt.size = 0;
+
+    /* read frames from the file */
+    while (av_read_frame(fmt_ctx, &pkt) >= 0) {
+        AVPacket orig_pkt = pkt;
+        do {
+            ret = decode_packet(&got_frame, 0);
+            if (ret < 0)
+                break;
+            pkt.data += ret;
+            pkt.size -= ret;
+        } while (pkt.size > 0);
+        av_free_packet(&orig_pkt);
+    }
+
+    /* flush cached frames */
+    pkt.data = NULL;
+    pkt.size = 0;
+    do {
+        decode_packet(&got_frame, 1);
+    } while (got_frame);
+
+end:
+    avcodec_close(video_dec_ctx);
+    avformat_close_input(&fmt_ctx);
+    av_frame_free(&frame);
+    return ret < 0;
+}