On 03.02.24 14:53, Andreas Rheinhardt wrote:
Thilo Borgmann via ffmpeg-devel:
Am 28.01.24 um 11:29 schrieb Anton Khirnov:
Quoting Thilo Borgmann via ffmpeg-devel (2024-01-25 16:39:19)
Am 25.01.24 um 11:04 schrieb Anton Khirnov:
Quoting Thilo Borgmann via ffmpeg-devel (2023-12-31 13:30:14)
---
libavcodec/webp.c | 50
+++++++++++++++++++++++++++++++++++++++++------
1 file changed, 44 insertions(+), 6 deletions(-)
diff --git a/libavcodec/webp.c b/libavcodec/webp.c
index 4fd107aa0c..58a20b73da 100644
--- a/libavcodec/webp.c
+++ b/libavcodec/webp.c
@@ -194,6 +194,7 @@ typedef struct WebPContext {
AVFrame *alpha_frame; /* AVFrame for alpha
data decompressed from VP8L */
AVPacket *pkt; /* AVPacket to be passed
to the underlying VP8 decoder */
AVCodecContext *avctx; /* parent AVCodecContext */
+ AVCodecContext *avctx_vp8; /* wrapper context for VP8
decoder */
Nested codec contexts are in general highly undesirable and should be
avoided whenever possible.
AFAICT we do it that way in the other codecs as well (cri, ftr, imm5,
tdsc, tiff). So what do you suggest to do to avoid having it nested?
Integrating the two decoders directly, as is done now.
With nesting it is very tricky to handle all the corner cases properly,
especially passing through all the options to the innner decoder, like
direct rendering, other user callbacks, etc. It should only be done as a
last resort and there should be a strong argument to do it this way.
IIUC that was what the patch still did some some versions ago.
It brought us the data races in animated files, decoupling the decoder
solving the issue.
If one keeps the codecs integrated, then one needs at the very least
change the check for whether to call ff_thread_finish_setup() as I did:
https://ffmpeg.org/pipermail/ffmpeg-devel/2024-January/320490.html
This will not be enough: E.g. changing the dimensions in VP8 code and
then reverting that change in WebP (as has been done in the earlier
version of your patch which made me propose that these decoders should
be separated) will have to be avoided.
I've a version of the animated webp decoder with coupled vp8 decoder
doing that size change and tsan is happy for me.
I had the impression ff_thread_finish_setup() blew it in the past which
is now avoided - am I wrong? Once your patches landed I'll post v10 and
we can check that again.
-Thilo
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