[FFmpeg-devel] [PATCH v6] avfilter/vf_blackframe: add slice threading

[Raja Rathour via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

v6: Rebased on master to resolve automated Patchwork application failures.
This patch adds slice threading support to the blackframe filter,
improving performance on multi-core systems.

Changes in v5:
- Removed meta-comments regarding C90 compliance as requested.
- Removed redundant null checks for ThreadData pointers.
- Renamed the thread results array to 'nb_black_pixels_per_slice' for clarity.

Signed-off-by: Raja Rathour <imraja729@gmail.com>
---
 libavfilter/vf_blackframe.c | 73 ++++++++++++++++---------------------
 1 file changed, 31 insertions(+), 42 deletions(-)

diff --git a/libavfilter/vf_blackframe.c b/libavfilter/vf_blackframe.c
index cb566d103d..fb531b8a4c 100644
--- a/libavfilter/vf_blackframe.c
+++ b/libavfilter/vf_blackframe.c
@@ -39,19 +39,20 @@
 
 typedef struct BlackFrameContext {
     const AVClass *class;
-    int bamount;          ///< black amount
-    int bthresh;          ///< black threshold
-    unsigned int frame;   ///< frame number
-    unsigned int nblack;  ///< number of black pixels counted so far
-    unsigned int last_keyframe; ///< frame number of the last received key-frame
+    int bamount;
+    int bthresh;
+    unsigned int frame;
+    unsigned int nblack;
+    unsigned int last_keyframe;
 } BlackFrameContext;
 
 typedef struct ThreadData {
-    const uint8_t *data; // Pointer to the image data
-    int linesize;        // How wide is the memory line
-    int bthresh;         // The black threshold
-    int width;           // Image width
-    unsigned int *counts; // POINTER to the array where threads write results
+    const uint8_t *data;
+    int linesize;
+    int bthresh;
+    int width;
+    int height; // Added height for cleaner slice math
+    unsigned int *counts;
 } ThreadData;
 
 static const enum AVPixelFormat pix_fmts[] = {
@@ -67,25 +68,21 @@ static const enum AVPixelFormat pix_fmts[] = {
 static int blackframe_slice(AVFilterContext *ctx, void *arg, int jobnr, int nb_jobs)
 {
     ThreadData *td = arg;
-    // Calculate vertical slice
-    int slice_start = (ctx->inputs[0]->h * jobnr) / nb_jobs;
-    int slice_end   = (ctx->inputs[0]->h * (jobnr+1)) / nb_jobs;
-    
-    // Safety check for pointers
-    if (!td || !td->data || !td->counts) return 0;
-
-    const uint8_t *p = td->data + slice_start * td->linesize;
-    unsigned int local_nblack = 0;
+    int slice_start = (td->height * jobnr) / nb_jobs;
+    int slice_end   = (td->height * (jobnr+1)) / nb_jobs;
     int x, y;
+    const uint8_t *p;
+    unsigned int black_pixels_count = 0;
+
+    p = td->data + slice_start * td->linesize;
 
     for (y = slice_start; y < slice_end; y++) {
         for (x = 0; x < td->width; x++)
-            local_nblack += p[x] < td->bthresh;
+            black_pixels_count += p[x] < td->bthresh;
         p += td->linesize;
     }
 
-    // Save my private count
-    td->counts[jobnr] = local_nblack;
+    td->counts[jobnr] = black_pixels_count;
     return 0;
 }
 
@@ -97,39 +94,31 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
     AVDictionary **metadata;
     char buf[32];
     ThreadData td;
+    int nb_threads, nb_jobs, i;
+    unsigned int *nb_black_pixels_per_slice;
+
+    nb_threads = ff_filter_get_nb_threads(ctx);
     
-    // 1. Get thread count
-    int nb_threads = ff_filter_get_nb_threads(ctx);
-    
-    // Allocate memory for thread results
-    unsigned int *thread_counts = av_calloc(nb_threads, sizeof(*thread_counts));
-    if (!thread_counts) {
-        av_log(ctx, AV_LOG_ERROR, "Failed to allocate thread_counts\n");
+    nb_black_pixels_per_slice = av_calloc(nb_threads, sizeof(*nb_black_pixels_per_slice));
+    if (!nb_black_pixels_per_slice)
         return AVERROR(ENOMEM);
-    }
 
-    // 3. Prepare the data package
     td.data = frame->data[0];
     td.linesize = frame->linesize[0];
     td.width = inlink->w;
+    td.height = inlink->h;
     td.bthresh = s->bthresh;
-    td.counts = thread_counts;
+    td.counts = nb_black_pixels_per_slice;
 
-    // 4. Run the threads!
-    // We calculate the exact number of jobs we are about to run
-    int nb_jobs = FFMIN(frame->height, nb_threads);
+    nb_jobs = FFMIN(td.height, nb_threads);
     
     ff_filter_execute(ctx, blackframe_slice, &td, NULL, nb_jobs);
 
-    // 5. THE REDUCE STEP: Sum up the results
     s->nblack = 0;
-    // Only sum up the jobs that actually ran
-    for (int i = 0; i < nb_jobs; i++) {
-        s->nblack += thread_counts[i];
+    for (i = 0; i < nb_jobs; i++) {
+        s->nblack += nb_black_pixels_per_slice[i];
     }
     
-    // --- FROM HERE DOWN, THE CODE IS THE SAME AS THE ORIGINAL ---
-    
     if (frame->flags & AV_FRAME_FLAG_KEY)
         s->last_keyframe = s->frame;
 
@@ -149,7 +138,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
     s->frame++;
     s->nblack = 0;
     
-    av_free(thread_counts);
+    av_free(nb_black_pixels_per_slice);
 
     return ff_filter_frame(inlink->dst->outputs[0], frame);
 }
-- 
2.48.1

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