feat(ffmpeg): FFmpeg additional metadata (#4396)

This change adds additional FFmpeg metadata from the video and data
streams. These streams can hold the start timecode which is very useful
in OpenTimelineIO applications.

I also added `av_guess_frame_rate()` which might be more robust than
just checking `stream->avg_frame_rate`, but I can also create a separate
PR if it is better to break it up.

It doesn't look like there are any FFmpeg tests in `testsuite`?

I tested with the DPEL ALab trailer and some Netflix Open Content
movies, and was able to see the timecode metadata in the OIIO image
attributes.

---------

Signed-off-by: Darby Johnston <darbyjohnston@yahoo.com>

src/doc/builtinplugins.rst

@@ -1252,6 +1252,9 @@ Some special attributes are used for movie files:
    * - ``FramesPerSecond``
      - int[2] (rational)
      - Frames per second
+   * - ``ffmpeg:TimeCode``
+     - string
+     - Start time timecode
 
 
 

src/ffmpeg.imageio/ffmpeginput.cpp

@@ -130,6 +130,7 @@ class FFmpegInput final : public ImageInput {
     std::vector<uint8_t> m_rgb_buffer;
     std::vector<int> m_video_indexes;
     int m_video_stream;
+    int m_data_stream;
     int64_t m_frames;
     int m_last_search_pos;
     int m_last_decoded_pos;
@@ -152,6 +153,7 @@ class FFmpegInput final : public ImageInput {
         m_rgb_buffer.clear();
         m_video_indexes.clear();
         m_video_stream     = -1;
+        m_data_stream      = -1;
         m_frames           = 0;
         m_last_search_pos  = 0;
         m_last_decoded_pos = 0;
@@ -263,6 +265,14 @@ FFmpegInput::open(const std::string& name, ImageSpec& spec)
         errorfmt("\"{}\" could not find a valid videostream", file_name);
         return false;
     }
+    for (unsigned int i = 0; i < m_format_context->nb_streams; i++) {
+        if (stream_codec(i)->codec_type == AVMEDIA_TYPE_DATA) {
+            if (m_data_stream < 0) {
+                m_data_stream = i;
+                break;
+            }
+        }
+    }
 
     // codec context for videostream
 #if USE_FFMPEG_3_1
@@ -309,9 +319,7 @@ FFmpegInput::open(const std::string& name, ImageSpec& spec)
                                & AV_CODEC_CAP_DELAY);
 
     AVStream* stream = m_format_context->streams[m_video_stream];
-    if (stream->avg_frame_rate.num != 0 && stream->avg_frame_rate.den != 0) {
-        m_frame_rate = stream->avg_frame_rate;
-    }
+    m_frame_rate     = av_guess_frame_rate(m_format_context, stream, NULL);
 
     m_frames     = stream->nb_frames;
     m_start_time = stream->start_time;
@@ -514,6 +522,26 @@ FFmpegInput::open(const std::string& name, ImageSpec& spec)
                               AV_DICT_IGNORE_SUFFIX))) {
         m_spec.attribute(tag->key, tag->value);
     }
+    tag = NULL;
+    if (m_data_stream >= 0) {
+        while ((
+            tag = av_dict_get(m_format_context->streams[m_data_stream]->metadata,
+                              "", tag, AV_DICT_IGNORE_SUFFIX))) {
+            if (strcmp(tag->key, "timecode") == 0) {
+                m_spec.attribute("ffmpeg:TimeCode", tag->value);
+                break;
+            }
+        }
+    }
+    tag = NULL;
+    while (
+        (tag = av_dict_get(m_format_context->streams[m_video_stream]->metadata,
+                           "", tag, AV_DICT_IGNORE_SUFFIX))) {
+        if (strcmp(tag->key, "timecode") == 0) {
+            m_spec.attribute("ffmpeg:TimeCode", tag->value);
+            break;
+        }
+    }
     int rat[2] = { m_frame_rate.num, m_frame_rate.den };
     m_spec.attribute("FramesPerSecond", TypeRational, &rat);
     m_spec.attribute("oiio:Movie", true);