[FFmpeg-devel] [PATCH] libavformat/mov: Accept known codepoints in 'colr'

[Steven Robertson]

This change relaxes the whitelist on reading color metadata in MOV/BMFF
containers. The whitelist on writing values is still in place.

As a consequence it also fixes an apparent bug in reading 'nclc' values.
The 'nclc' spec [1] is in harmony with ISO 23001-8 for the values it
lists, but the code getting removed was remapping 5->6 and 6->7 for
primaries, which is incorrect, and was remapping 6->5 for color matrix
("colorspace" in the code), which is equivalent but an unnecessary
inconsistency. This logic error doesn't appear in movenc.

Removing the whitelist allows proper conversion when the source codec
relies on the container for proper signaling of newer codepoints, such
as DNxHR and VP9. If converting to a codec or container that has updated
its spec to include the new codepoints, the metadata will be preserved.
If going back to MOV/BMFF, the output whitelist will still kick in, so
this won't result in out-of-spec files being created.

[1] https://developer.apple.com/library/mac/technotes/tn2162/_index.html

Signed-off-by: Steven Robertson <steven at strobe.cc>
---
 libavformat/mov.c | 40 +++++++++-------------------------------
 1 file changed, 9 insertions(+), 31 deletions(-)

diff --git a/libavformat/mov.c b/libavformat/mov.c
index 7c8f784..6450d52 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -1324,38 +1324,16 @@ static int mov_read_colr(MOVContext *c, AVIOContext *pb, MOVAtom atom)
             st->codecpar->color_range = AVCOL_RANGE_JPEG;
         else
             st->codecpar->color_range = AVCOL_RANGE_MPEG;
-        /* 14496-12 references JPEG XR specs (rather than the more complete
-         * 23001-8) so some adjusting is required */
-        if (color_primaries >= AVCOL_PRI_FILM)
-            color_primaries = AVCOL_PRI_UNSPECIFIED;
-        if ((color_trc >= AVCOL_TRC_LINEAR &&
-             color_trc <= AVCOL_TRC_LOG_SQRT) ||
-            color_trc >= AVCOL_TRC_BT2020_10)
-            color_trc = AVCOL_TRC_UNSPECIFIED;
-        if (color_matrix >= AVCOL_SPC_BT2020_NCL)
-            color_matrix = AVCOL_SPC_UNSPECIFIED;
-        st->codecpar->color_primaries = color_primaries;
-        st->codecpar->color_trc       = color_trc;
-        st->codecpar->color_space     = color_matrix;
-    } else if (!strncmp(color_parameter_type, "nclc", 4)) {
-        /* color primaries, Table 4-4 */
-        switch (color_primaries) {
-        case 1: st->codecpar->color_primaries = AVCOL_PRI_BT709; break;
-        case 5: st->codecpar->color_primaries = AVCOL_PRI_SMPTE170M; break;
-        case 6: st->codecpar->color_primaries = AVCOL_PRI_SMPTE240M; break;
-        }
-        /* color transfer, Table 4-5 */
-        switch (color_trc) {
-        case 1: st->codecpar->color_trc = AVCOL_TRC_BT709; break;
-        case 7: st->codecpar->color_trc = AVCOL_TRC_SMPTE240M; break;
-        }
-        /* color matrix, Table 4-6 */
-        switch (color_matrix) {
-        case 1: st->codecpar->color_space = AVCOL_SPC_BT709; break;
-        case 6: st->codecpar->color_space = AVCOL_SPC_BT470BG; break;
-        case 7: st->codecpar->color_space = AVCOL_SPC_SMPTE240M; break;
-        }
     }
+    if (color_primaries >= AVCOL_PRI_NB)
+        color_primaries = AVCOL_PRI_UNSPECIFIED;
+    if (color_trc >= AVCOL_TRC_NB)
+        color_trc = AVCOL_TRC_UNSPECIFIED;
+    if (color_matrix >= AVCOL_SPC_NB)
+        color_matrix = AVCOL_SPC_UNSPECIFIED;
+    st->codecpar->color_primaries = color_primaries;
+    st->codecpar->color_trc       = color_trc;
+    st->codecpar->color_space     = color_matrix;
     av_log(c->fc, AV_LOG_TRACE, "\n");

     return 0;
--
2.8.0.rc2