On 4/25/2021 10:27 PM, Andreas Rheinhardt wrote:
Lynne:
From 097aed2ac33dda0bb2052d8b0402711ce95079ba Mon Sep 17 00:00:00 2001
From: Lynne <d...@lynne.ee>
Date: Sat, 23 Jan 2021 19:56:18 +0100
Subject: [PATCH] avpacket: ABI bump additions
---
libavcodec/avpacket.c | 5 +++++
libavcodec/packet.h | 21 +++++++++++++++++++++
2 files changed, 26 insertions(+)
diff --git a/libavcodec/avpacket.c b/libavcodec/avpacket.c
index e32c467586..03b73b3b53 100644
--- a/libavcodec/avpacket.c
+++ b/libavcodec/avpacket.c
@@ -382,6 +382,10 @@ int av_packet_copy_props(AVPacket *dst, const AVPacket
*src)
dst->flags = src->flags;
dst->stream_index = src->stream_index;
+ i = av_buffer_replace(&dst->opaque_ref, src->opaque_ref);
+ if (i < 0)
+ return i;
1. Don't use i here; add a new variable.
2. Up until now, av_packet_ref() and av_packet_copy_props() treat the
destination packet as uninitialized and make no attempt at unreferencing
its content; yet you try to reuse opaque_ref. Even worse, you might
return potentially dangerous packets: If the properties were
uninitialized and av_packet_copy_props() failed, then the caller were
not allowed to unreference the packet even when the non-properties were
set to sane values. The easiest way to fix this is to move setting
opaque ref to the place after initializing side_data below and either
set dst->opaque_ref to NULL before av_buffer_replace() or to not use
av_buffer_replace(). It may also be best to unref it again if copying
side data fails.
Fwiw, the idea is that once sizeof(AVPacket) is not a part of the ABI
anymore, there will no longer be such thing as an uninitialized packet
as far as proper API usage goes. And as such the lines below...
+
dst->side_data = NULL;
dst->side_data_elems = 0;
^^^^^^^^^^^^^^^^^^^^
...should be replaced by a av_packet_free_side_data(dst) call.
Similarly, at that point using av_buffer_replace() on opaque_ref should
become safe. But until then, you're right that doing so *will* go wrong
on uninitialized packets.
for (i = 0; i < src->side_data_elems; i++) {
@@ -403,6 +407,7 @@ int av_packet_copy_props(AVPacket *dst, const AVPacket *src)
void av_packet_unref(AVPacket *pkt)
{
av_packet_free_side_data(pkt);
+ av_buffer_unref(&pkt->opaque_ref);
av_buffer_unref(&pkt->buf);
get_packet_defaults(pkt);
}
diff --git a/libavcodec/packet.h b/libavcodec/packet.h
index fad8341c12..c29ad18a2b 100644
--- a/libavcodec/packet.h
+++ b/libavcodec/packet.h
@@ -383,6 +383,27 @@ typedef struct AVPacket {
int64_t duration;
int64_t pos; ///< byte position in stream, -1 if unknown
+
+ /**
+ * for some private data of the user
+ */
+ void *opaque;
The corresponding AVFrame field is copied when copying props.
+
+ /**
+ * AVBufferRef for free use by the API user. FFmpeg will never check the
+ * contents of the buffer ref. FFmpeg calls av_buffer_unref() on it when
+ * the packet is unreferenced. av_packet_copy_props() calls create a new
+ * reference with av_buffer_ref() for the target packet's opaque_ref field.
+ *
+ * This is unrelated to the opaque field, although it serves a similar
+ * purpose.
+ */
+ AVBufferRef *opaque_ref;
+
+ /**
+ * Time base of the packet's timestamps.
+ */
+ AVRational time_base;
} AVPacket;
#if FF_API_INIT_PACKET
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