[FFmpeg-devel] [PATCH v3 1/2] vf_crop: Add support for cropping hardware frames

[Mark Thompson]

Set the cropping fields in the AVFrame.
---
 libavfilter/vf_crop.c | 74 +++++++++++++++++++++++++++++--------------
 1 file changed, 51 insertions(+), 23 deletions(-)

There is the slightly unfortunate effect the filter links don't carry the cropping information, so we don't know how big the cropped output is in following links until we actually get a frame.

For example, to get the middle ninth of a stream:

./ffmpeg_g -y -hwaccel vaapi -hwaccel_device /dev/dri/renderD128 -hwaccel_output_format vaapi -i in.mp4 -an -vf "crop=iw/3:ih/3:iw/3:ih/3,scale_vaapi=iw/3:ih/3" -c:v h264_vaapi out.mp4

Without the extra arguments to scale it will take the cropped part correctly but then scale it to the original size.

diff --git a/libavfilter/vf_crop.c b/libavfilter/vf_crop.c
index 84be4c7d0d..7f6b0f03d3 100644
--- a/libavfilter/vf_crop.c
+++ b/libavfilter/vf_crop.c
@@ -98,9 +98,17 @@ static int query_formats(AVFilterContext *ctx)
 
     for (fmt = 0; av_pix_fmt_desc_get(fmt); fmt++) {
         const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(fmt);
-        if (!(desc->flags & (AV_PIX_FMT_FLAG_HWACCEL | AV_PIX_FMT_FLAG_BITSTREAM)) &&
-            !((desc->log2_chroma_w || desc->log2_chroma_h) && !(desc->flags & AV_PIX_FMT_FLAG_PLANAR)) &&
-            (ret = ff_add_format(&formats, fmt)) < 0)
+        if (desc->flags & AV_PIX_FMT_FLAG_BITSTREAM)
+            continue;
+        if (!(desc->flags & AV_PIX_FMT_FLAG_HWACCEL)) {
+            // Not usable if there is any subsampling but the format is
+            // not planar (e.g. YUYV422).
+            if ((desc->log2_chroma_w || desc->log2_chroma_h) &&
+                !(desc->flags & AV_PIX_FMT_FLAG_PLANAR))
+                continue;
+        }
+        ret = ff_add_format(&formats, fmt);
+        if (ret < 0)
             return ret;
     }
 
@@ -157,8 +165,14 @@ static int config_input(AVFilterLink *link)
     s->var_values[VAR_POS]   = NAN;
 
     av_image_fill_max_pixsteps(s->max_step, NULL, pix_desc);
-    s->hsub = pix_desc->log2_chroma_w;
-    s->vsub = pix_desc->log2_chroma_h;
+
+    if (pix_desc->flags & AV_PIX_FMT_FLAG_HWACCEL) {
+        s->hsub = 1;
+        s->vsub = 1;
+    } else {
+        s->hsub = pix_desc->log2_chroma_w;
+        s->vsub = pix_desc->log2_chroma_h;
+    }
 
     if ((ret = av_expr_parse_and_eval(&res, (expr = s->w_expr),
                                       var_names, s->var_values,
@@ -237,9 +251,15 @@ fail_expr:
 static int config_output(AVFilterLink *link)
 {
     CropContext *s = link->src->priv;
+    const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(link->format);
 
-    link->w = s->w;
-    link->h = s->h;
+    if (desc->flags & AV_PIX_FMT_FLAG_HWACCEL) {
+        // Hardware frames adjust the cropping regions rather than
+        // changing the frame size.
+    } else {
+        link->w = s->w;
+        link->h = s->h;
+    }
     link->sample_aspect_ratio = s->out_sar;
 
     return 0;
@@ -252,9 +272,6 @@ static int filter_frame(AVFilterLink *link, AVFrame *frame)
     const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(link->format);
     int i;
 
-    frame->width  = s->w;
-    frame->height = s->h;
-
     s->var_values[VAR_N] = link->frame_count_out;
     s->var_values[VAR_T] = frame->pts == AV_NOPTS_VALUE ?
         NAN : frame->pts * av_q2d(link->time_base);
@@ -285,22 +302,33 @@ static int filter_frame(AVFilterLink *link, AVFrame *frame)
             (int)s->var_values[VAR_N], s->var_values[VAR_T], s->var_values[VAR_POS],
             s->x, s->y, s->x+s->w, s->y+s->h);
 
-    frame->data[0] += s->y * frame->linesize[0];
-    frame->data[0] += s->x * s->max_step[0];
-
-    if (!(desc->flags & AV_PIX_FMT_FLAG_PAL || desc->flags & FF_PSEUDOPAL)) {
-        for (i = 1; i < 3; i ++) {
-            if (frame->data[i]) {
-                frame->data[i] += (s->y >> s->vsub) * frame->linesize[i];
-                frame->data[i] += (s->x * s->max_step[i]) >> s->hsub;
+    if (desc->flags & AV_PIX_FMT_FLAG_HWACCEL) {
+        frame->crop_top   += s->y;
+        frame->crop_left  += s->x;
+        frame->crop_bottom = frame->height - frame->crop_top - frame->crop_bottom - s->h;
+        frame->crop_right  = frame->width  - frame->crop_left - frame->crop_right - s->w;
+
+    } else {
+        frame->width  = s->w;
+        frame->height = s->h;
+
+        frame->data[0] += s->y * frame->linesize[0];
+        frame->data[0] += s->x * s->max_step[0];
+
+        if (!(desc->flags & AV_PIX_FMT_FLAG_PAL || desc->flags & FF_PSEUDOPAL)) {
+            for (i = 1; i < 3; i ++) {
+                if (frame->data[i]) {
+                    frame->data[i] += (s->y >> s->vsub) * frame->linesize[i];
+                    frame->data[i] += (s->x * s->max_step[i]) >> s->hsub;
+                }
             }
         }
-    }
 
-    /* alpha plane */
-    if (frame->data[3]) {
-        frame->data[3] += s->y * frame->linesize[3];
-        frame->data[3] += s->x * s->max_step[3];
+        /* alpha plane */
+        if (frame->data[3]) {
+            frame->data[3] += s->y * frame->linesize[3];
+            frame->data[3] += s->x * s->max_step[3];
+        }
     }
 
     return ff_filter_frame(link->dst->outputs[0], frame);
-- 
2.19.2