[FFmpeg-cvslog] avcodec/vp8: Enforce key-frame only for WebP

[Andreas Rheinhardt]

ffmpeg | branch: master | Andreas Rheinhardt <andreas.rheinhardt at outlook.com> | Tue Jan 30 21:04:43 2024 +0100| [4b8b1415ae7709351eeab4037d0ef2e20bf9f7bd] | committer: Andreas Rheinhardt

avcodec/vp8: Enforce key-frame only for WebP

VP8-in-WebP only uses key frame encoding (see [1]), yet this
is currently not enforced. This commit does so in order to
make output reproducible with frame-threading as the VP8 decoder's
update_thread_context is not called at all when using decoding
VP8-in-WebP (as this is unnecessary for key frame-only streams).

[1]: https://developers.google.com/speed/webp/docs/riff_container

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=4b8b1415ae7709351eeab4037d0ef2e20bf9f7bd
---

 libavcodec/vp8.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/libavcodec/vp8.c b/libavcodec/vp8.c
index 83c60adeb0..7972775a1c 100644
--- a/libavcodec/vp8.c
+++ b/libavcodec/vp8.c
@@ -2665,7 +2665,11 @@ int vp78_decode_frame(AVCodecContext *avctx, AVFrame *rframe, int *got_frame,
     if (ret < 0)
         goto err;
 
-    if (s->actually_webp) {
+    if (!is_vp7 && s->actually_webp) {
+        // VP8 in WebP is supposed to be intra-only. Enforce this here
+        // to ensure that output is reproducible with frame-threading.
+        if (!s->keyframe)
+            return AVERROR_INVALIDDATA;
         // avctx->pix_fmt already set in caller.
     } else if (!is_vp7 && s->pix_fmt == AV_PIX_FMT_NONE) {
         s->pix_fmt = get_pixel_format(s);