On Sat, 13 Mar 2021, James Almer wrote:
Signed-off-by: James Almer <jamr...@gmail.com>
---
Setting pkt->size to 0 but leaving pkt->data pointing to the frame ensures that
the packet isn't mistaken for an empty one, and prevents wrong use of the data
pointer in case av_packet_make_writable() is called on it (The resulting packet
will be the same as if you call it on an empty one).
I decided to set the opaque field of the AVBufferRef to the frame pointer so
we can do something like ensure pkt->size is 0 and pkt->data is equal to it
before trying to treat pkt->data as an AVFrame, but i'm not sure if that could
be done now, or only after a major bump (e.g. 4.3 lavf/lavd and 4.4 lavc at
runtime, where demuxers like the vapoursynth one propagate packets to the
wrapped_avframe decoder, and if the latter does the above check, it would
fail).
libavcodec/wrapped_avframe.c | 23 ++++-------------------
1 file changed, 4 insertions(+), 19 deletions(-)
Is using sizeof(AVFrame) an issue apart from that it is not part of ABI?
Is there an actual issue this patch fix?
Isn't it a problem that the packet may not have correct padding now,
becaue you allocate a 0 sized av_buffer? We had a bug because of this, and
I fixed it in 436f00b10c062b75c7aab276c4a7d64524bd0444, which was caused
by av_buffer_realloc(&avpkt->buf, avpkt->size +
AV_INPUT_BUFFER_PADDING_SIZE) calls in the encode function removed in
93016f5d1d280f9cb7856883af287fa66affc04c. More info in this thread:
http://lists.ffmpeg.org/pipermail/ffmpeg-devel/2017-February/207329.html
I guess the fundamental problem of WRAPPED_AVFRAME is that deep copying it
is not supported, but you don't exactly disallow that by using a size of
0, because the deep copying (making it writable) will still return
success, but the optimal thing would be if it would fail or correctly
clone the AVFrame. Or am I missing something? Maybe we need something
similar to AVFrame->hw_frames_ctx for AVPacket?
It is also debatable if lowering the packet size is a breaking change or
not, because previously people could have had an assert in their code
making sure it is not used with a library built with an AVFrame smaller
than what they are using...
So unless we try to fix something specific with this patch maybe it is
better to not touch it unless we have plans how to fix all known issues
with wrapped avframes?
And also libavdevice/kmsgrab.c need some changes too if a new format is to
be followed.
Regards,
Marton
diff --git a/libavcodec/wrapped_avframe.c b/libavcodec/wrapped_avframe.c
index 85ff32d13a..c921990024 100644
--- a/libavcodec/wrapped_avframe.c
+++ b/libavcodec/wrapped_avframe.c
@@ -44,32 +44,20 @@ static int wrapped_avframe_encode(AVCodecContext *avctx,
AVPacket *pkt,
const AVFrame *frame, int *got_packet)
{
AVFrame *wrapped = av_frame_clone(frame);
- uint8_t *data;
- int size = sizeof(*wrapped) + AV_INPUT_BUFFER_PADDING_SIZE;
if (!wrapped)
return AVERROR(ENOMEM);
- data = av_mallocz(size);
- if (!data) {
- av_frame_free(&wrapped);
- return AVERROR(ENOMEM);
- }
-
- pkt->buf = av_buffer_create(data, size,
- wrapped_avframe_release_buffer, NULL,
+ pkt->buf = av_buffer_create((uint8_t *)wrapped, 0,
+ wrapped_avframe_release_buffer, wrapped,
AV_BUFFER_FLAG_READONLY);
if (!pkt->buf) {
av_frame_free(&wrapped);
- av_freep(&data);
return AVERROR(ENOMEM);
}
- av_frame_move_ref((AVFrame*)data, wrapped);
- av_frame_free(&wrapped);
-
- pkt->data = data;
- pkt->size = sizeof(*wrapped);
+ pkt->data = (uint8_t *)wrapped;
+ pkt->size = 0;
pkt->flags |= AV_PKT_FLAG_KEY;
*got_packet = 1;
@@ -87,9 +75,6 @@ static int wrapped_avframe_decode(AVCodecContext *avctx, void
*data,
return AVERROR(EPERM);
}
- if (pkt->size < sizeof(AVFrame))
- return AVERROR(EINVAL);
-
in = (AVFrame*)pkt->data;
out = data;
--
2.30.2
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