[FFmpeg-devel] [PATCH] avfilter/image2: Add source file path and basename to each packet side data.

[Alexandre Heitor Schmidt]

This is the second time I'm submiting this patch, now modified to be
less intrusive, as sugested by Marton Balint, and hopefully without git
send-email messing up with the diff by replacing '@' within
documentation entries.

The patch modifies image2 filter to make available two special metadata
entries called source_path and source_file, which represents,
respectively, the complete path to the source image for the current
frame and the basename i.e. the file name related to the current frame.
These can then be used by filters like drawtext and others.

doc/filters: The documentation for drawtext was also updated and an usage
example was added.

Fixes #2874.

Signed-off-by: Alexandre Heitor Schmidt <alexandre.schmidt at gmail.com>
---
 doc/filters.texi      | 15 +++++++++++++--
 libavformat/img2.h    |  2 ++
 libavformat/img2dec.c | 28 ++++++++++++++++++++++++++++
 3 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/doc/filters.texi b/doc/filters.texi
index c543203ce3..15498aee0d 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -9723,8 +9723,12 @@ Available metadata can be identified by inspecting entries
 starting with TAG included within each frame section
 printed by running @code{ffprobe -show_frames}.
 
-String metadata generated in filters leading to
-the drawtext filter are also available.
+String metadata generated in filters leading to the drawtext filter are also
+available. For example, image2 filter generates two special metadata fields
+called @var{source_path} and @var{source_basename} for each input frame
+generated from a single image. @var{source_path} contains the entire path
+to input filename, while @var{source_basename} contains the equivalent
+to @code{basename(source_path)}.
 
 @item n, frame_num
 The frame number, starting from 0.
@@ -9872,6 +9876,13 @@ drawtext=fontfile=FreeSans.ttf:text=DOG:fontsize=24:x=10:y=20+24-max_glyph_a,
 drawtext=fontfile=FreeSans.ttf:text=cow:fontsize=24:x=80:y=20+24-max_glyph_a
 @end example
 
+ at item
+Plot special @var{source_basename} metadata, extracted from each input frame, or
+the string "NA" if the metadata is not defined.
+ at example
+drawtext="fontsize=20:fontcolor=white:fontfile=FreeSans.ttf:text='%{metadata\:source_basename\:NA}':x=10:y=10"
+ at end example
+
 @end itemize
 
 For more information about libfreetype, check:
diff --git a/libavformat/img2.h b/libavformat/img2.h
index 0e5b374a6b..8208c1f58b 100644
--- a/libavformat/img2.h
+++ b/libavformat/img2.h
@@ -74,5 +74,7 @@ extern const AVOption ff_img_options[];
 
 int ff_img_read_header(AVFormatContext *s1);
 
+int add_filename_as_pkt_side_data(char *filename, AVPacket *pkt);
+
 int ff_img_read_packet(AVFormatContext *s1, AVPacket *pkt);
 #endif
diff --git a/libavformat/img2dec.c b/libavformat/img2dec.c
index f8b4a655a5..3fb7aa7967 100644
--- a/libavformat/img2dec.c
+++ b/libavformat/img2dec.c
@@ -374,6 +374,32 @@ int ff_img_read_header(AVFormatContext *s1)
     return 0;
 }
 
+/**
+ * Add this frame's source path and basename to packet's sidedata
+ * as a dictionary, so it can be used by filters like 'drawtext'.
+ */
+int add_filename_as_pkt_side_data(char *filename, AVPacket *pkt) {
+    uint8_t* metadata;
+    int metadata_len;
+    AVDictionary *d = NULL;
+    char *packed_metadata = NULL;
+
+    av_dict_set(&d, "source_path", filename, 0);
+    av_dict_set(&d, "source_basename", av_basename(filename), 0);
+
+    packed_metadata = av_packet_pack_dictionary(d, &metadata_len);
+    if (!packed_metadata)
+        return AVERROR(ENOMEM);
+    if (!(metadata = av_packet_new_side_data(pkt, AV_PKT_DATA_STRINGS_METADATA, metadata_len))) {
+        av_freep(&packed_metadata);
+        return AVERROR(ENOMEM);
+    }
+    memcpy(metadata, packed_metadata, metadata_len);
+    av_freep(&packed_metadata);
+
+    return 0;
+}
+
 int ff_img_read_packet(AVFormatContext *s1, AVPacket *pkt)
 {
     VideoDemuxData *s = s1->priv_data;
@@ -485,6 +511,8 @@ int ff_img_read_packet(AVFormatContext *s1, AVPacket *pkt)
 
     if (s->is_pipe)
         pkt->pos = avio_tell(f[0]);
+    else if ( (res = add_filename_as_pkt_side_data(filename, pkt)) != 0 )
+        goto fail;
 
     pkt->size = 0;
     for (i = 0; i < 3; i++) {
-- 
2.17.1