[FFmpeg-devel] [crop support for matroska demuxer, V4 3/3] libavformat\matroskadec.c: crop support for matroska demuxer.

[Dmitrii Ovchinnikov]

From: Dmitrii Ovchinnikov <ovchinnikov.dmitrii at gmail.com>

In webm specification, it supports cropping information. (https://www.webmproject.org/docs/container/)
In ffmpeg, the implementation of webm is a subset of matroska. In matroskadec.c, those cropping related four fields are forced to 0.

for the sample file with crop (crop_bottom =8, crop_top=crop_left=crop_right=0.)
ffmpeg.exe -i  test_with_container_crop.webm -pix_fmt yuv420p -y output.yuv

original ffmpeg code - the output.yuv resolution is 1920x1088
changed code - the output.yuv resolution is 1920x1080

---
 libavformat/matroskadec.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
index d582f566a2..2023fd4977 100644
--- a/libavformat/matroskadec.c
+++ b/libavformat/matroskadec.c
@@ -210,6 +210,10 @@ typedef struct MatroskaTrackVideo {
     uint64_t pixel_width;
     uint64_t pixel_height;
     EbmlBin  color_space;
+    uint64_t pixel_cropt;
+    uint64_t pixel_cropl;
+    uint64_t pixel_cropb;
+    uint64_t pixel_cropr;
     uint64_t display_unit;
     uint64_t interlaced;
     uint64_t field_order;
@@ -517,10 +521,10 @@ static EbmlSyntax matroska_track_video[] = {
     { MATROSKA_ID_VIDEOALPHAMODE,      EBML_UINT,  0, 0, offsetof(MatroskaTrackVideo, alpha_mode), { .u = 0 } },
     { MATROSKA_ID_VIDEOCOLOR,          EBML_NEST,  0, sizeof(MatroskaTrackVideoColor), offsetof(MatroskaTrackVideo, color), { .n = matroska_track_video_color } },
     { MATROSKA_ID_VIDEOPROJECTION,     EBML_NEST,  0, 0, offsetof(MatroskaTrackVideo, projection), { .n = matroska_track_video_projection } },
-    { MATROSKA_ID_VIDEOPIXELCROPB,     EBML_NONE },
-    { MATROSKA_ID_VIDEOPIXELCROPT,     EBML_NONE },
-    { MATROSKA_ID_VIDEOPIXELCROPL,     EBML_NONE },
-    { MATROSKA_ID_VIDEOPIXELCROPR,     EBML_NONE },
+    { MATROSKA_ID_VIDEOPIXELCROPT,     EBML_UINT,  0, 0, offsetof(MatroskaTrackVideo, pixel_cropt), {.u = 0 } },
+    { MATROSKA_ID_VIDEOPIXELCROPL,     EBML_UINT,  0, 0, offsetof(MatroskaTrackVideo, pixel_cropl), {.u = 0 } },
+    { MATROSKA_ID_VIDEOPIXELCROPB,     EBML_UINT,  0, 0, offsetof(MatroskaTrackVideo, pixel_cropb), {.u = 0 } },
+    { MATROSKA_ID_VIDEOPIXELCROPR,     EBML_UINT,  0, 0, offsetof(MatroskaTrackVideo, pixel_cropr), {.u = 0 } },
     { MATROSKA_ID_VIDEODISPLAYUNIT,    EBML_UINT,  0, 0, offsetof(MatroskaTrackVideo, display_unit), { .u= MATROSKA_VIDEO_DISPLAYUNIT_PIXELS } },
     { MATROSKA_ID_VIDEOFLAGINTERLACED, EBML_UINT,  0, 0, offsetof(MatroskaTrackVideo, interlaced),  { .u = MATROSKA_VIDEO_INTERLACE_FLAG_UNDETERMINED } },
     { MATROSKA_ID_VIDEOFIELDORDER,     EBML_UINT,  0, 0, offsetof(MatroskaTrackVideo, field_order), { .u = MATROSKA_VIDEO_FIELDORDER_UNDETERMINED } },
@@ -2879,6 +2883,11 @@ static int matroska_parse_tracks(AVFormatContext *s)
             st->codecpar->width      = track->video.pixel_width;
             st->codecpar->height     = track->video.pixel_height;
 
+            st->codecpar->container_crop_top    = track->video.pixel_cropt;
+            st->codecpar->container_crop_left   = track->video.pixel_cropl;
+            st->codecpar->container_crop_bottom = track->video.pixel_cropb;
+            st->codecpar->container_crop_right  = track->video.pixel_cropr;
+
             if (track->video.interlaced == MATROSKA_VIDEO_INTERLACE_FLAG_INTERLACED)
                 st->codecpar->field_order = mkv_field_order(matroska, track->video.field_order);
             else if (track->video.interlaced == MATROSKA_VIDEO_INTERLACE_FLAG_PROGRESSIVE)
-- 
2.30.0.windows.2