[FFmpeg-devel] [PATCH] libavfilter/thumbnail filter, copy buffers instead of reference

[Chris Kennedy]

This fixes the buffer handling in the thumbnail filter, it seems that the
referencing buffers it does isn't safe (could be hundreds of them held in
ref) and the main ffmpeg buffer handling can fail.

It now just grabs the video buffers and copies them, frees the frame
immediately, and works just the same now, and doesn't use 1.7 Gig of memory
in my tests with 300 buffers, it uses around 100 meg max now.  There was
obviously something nasty in how it was doing this.



diff --git a/libavfilter/vf_thumbnail.c b/libavfilter/vf_thumbnail.c
index 1883154..82b8ebe 100644
--- a/libavfilter/vf_thumbnail.c
+++ b/libavfilter/vf_thumbnail.c
@@ -137,9 +137,6 @@ static int filter_frame(AVFilterLink *inlink, AVFrame
*frame)
     int *hist = thumb->frames[thumb->n].histogram;
     const uint8_t *p = frame->data[0];

-    // keep a reference of each frame
-    thumb->frames[thumb->n].buf = frame;
-
     // update current frame RGB histogram
     for (j = 0; j < inlink->h; j++) {
         for (i = 0; i < inlink->w; i++) {
@@ -150,6 +147,17 @@ static int filter_frame(AVFilterLink *inlink, AVFrame
*frame)
         p += frame->linesize[0];
     }

+    // Copy orginal frame into buffer(s)
+    thumb->frames[thumb->n].buf = ff_get_video_buffer(inlink, inlink->w,
inlink->h);
+    if (!thumb->frames[thumb->n].buf) {
+        av_frame_free(&frame);
+        return AVERROR(ENOMEM);
+    }
+    av_frame_copy_props(thumb->frames[thumb->n].buf, frame);
+
+    // Free original frame we have copied
+    av_frame_free(&frame);
+
     // no selection until the buffer of N frames is filled up
     thumb->n++;
     if (thumb->n < thumb->n_frames)


I previously sent a patch which was wrong, and just avoided the issue for
certain media but hit it on others, this should fix it for good now (since
it also doesn't alter the chosen thumbnail that results)...


Thanks,
Chris
---
Chris Kennedy
Video Engineer
CrunchyRoll - http://www.crunchyroll.com



-- 
---
Chris Kennedy
-------------- next part --------------
diff --git a/libavfilter/vf_thumbnail.c b/libavfilter/vf_thumbnail.c
index 1883154..a1272a0 100644
--- a/libavfilter/vf_thumbnail.c
+++ b/libavfilter/vf_thumbnail.c
@@ -142,7 +142,8 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)

     // update current frame RGB histogram
     for (j = 0; j < inlink->h; j++) {
-        for (i = 0; i < inlink->w; i++) {
+        // last third of image, walk every 3 bytes/pixels reading RGB
+        for (i = 0; i < inlink->w/3; i++) {
             hist[0*256 + p[i*3    ]]++;
             hist[1*256 + p[i*3 + 1]]++;
             hist[2*256 + p[i*3 + 2]]++;