[FFmpeg-devel] [PATCH 1/3] lavc/pngdec: honor skip_frame option

[Matthieu Bouron]

From: Matthieu Bouron <matthieu.bouron at stupeflix.com>

---
 libavcodec/pngdec.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index 4cfdc58..5b2befe 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -1087,6 +1087,13 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
     for (;;) {
         length = bytestream2_get_bytes_left(&s->gb);
         if (length <= 0) {
+
+            if (avctx->codec_id == AV_CODEC_ID_PNG &&
+                avctx->skip_frame == AVDISCARD_ALL) {
+                av_frame_set_metadata(p, metadata);
+                return 0;
+            }
+
             if (CONFIG_APNG_DECODER && avctx->codec_id == AV_CODEC_ID_APNG && length == 0) {
                 if (!(s->state & PNG_IDAT))
                     return 0;
@@ -1114,6 +1121,22 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
                 ((tag >> 8) & 0xff),
                 ((tag >> 16) & 0xff),
                 ((tag >> 24) & 0xff), length);
+
+        if (avctx->codec_id == AV_CODEC_ID_PNG &&
+            avctx->skip_frame == AVDISCARD_ALL) {
+            int i, found = 0;
+            static const int tags[] = { MKTAG('I', 'H', 'D', 'R'), MKTAG('t', 'E', 'X', 't'), MKTAG('I', 'D', 'A', 'T') };
+            for (i = 0; i < FF_ARRAY_ELEMS(tags); i++) {
+                if (tag == tags[i]) {
+                    found = 1;
+                    break;
+                }
+            }
+            if (!found) {
+                goto skip_tag;
+            }
+        }
+
         switch (tag) {
         case MKTAG('I', 'H', 'D', 'R'):
             if ((ret = decode_ihdr_chunk(avctx, s, length)) < 0)
@@ -1181,6 +1204,11 @@ skip_tag:
         }
     }
 exit_loop:
+    if (avctx->codec_id == AV_CODEC_ID_PNG &&
+        avctx->skip_frame == AVDISCARD_ALL) {
+        av_frame_set_metadata(p, metadata);
+        return 0;
+    }
 
     if (s->bits_per_pixel <= 4)
         handle_small_bpp(s, p);
@@ -1278,6 +1306,12 @@ static int decode_frame_png(AVCodecContext *avctx,
     if ((ret = decode_frame_common(avctx, s, p, avpkt)) < 0)
         goto the_end;
 
+    if (avctx->skip_frame == AVDISCARD_ALL) {
+        *got_frame = 0;
+        ret = bytestream2_tell(&s->gb);
+        goto the_end;
+    }
+
     if ((ret = av_frame_ref(data, s->picture.f)) < 0)
         return ret;
 
-- 
2.6.1