Re: [FFmpeg-devel] [PATCH 1/3] avformat/avio: add resizeable field to AVIOContext

2015-04-27 Thread wm4 
On Mon, 27 Apr 2015 04:50:27 +0200
Michael Niedermayer michae...@gmx.at wrote:

 On Tue, Apr 21, 2015 at 02:23:19PM +0200, wm4 wrote:
  On Tue, 21 Apr 2015 13:22:00 +0200
  Michael Niedermayer michae...@gmx.at wrote:
  
   This indicates that its safe to use av_free/av_malloc on the IO context
   
   Signed-off-by: Michael Niedermayer michae...@gmx.at
   ---
libavformat/avio.h|7 +++
libavformat/aviobuf.c |1 +
libavformat/segment.c |1 +
libavformat/wtvdec.c  |3 ++-
4 files changed, 11 insertions(+), 1 deletion(-)
   
   diff --git a/libavformat/avio.h b/libavformat/avio.h
   index 51913e3..73d1645 100644
   --- a/libavformat/avio.h
   +++ b/libavformat/avio.h
   @@ -196,6 +196,13 @@ typedef struct AVIOContext {
 * This field is internal to libavformat and access from outside is 
   not allowed.
 */
int orig_buffer_size;
   +
   +/**
   + * The io buffer can be resized or freed with av_free / av_malloc.
   + * The user application does not keep a private copy of the buffer 
   pointer
   + * which would become stale on such reallocation.
   + */
   +int resizeable;
} AVIOContext;

/* unbuffered I/O */
   diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
   index 7de59f1..b32ff9f 100644
   --- a/libavformat/aviobuf.c
   +++ b/libavformat/aviobuf.c
   @@ -793,6 +793,7 @@ int ffio_fdopen(AVIOContext **s, URLContext *h)
(*s)-read_seek  = (int64_t (*)(void *, int, int64_t, 
   int))h-prot-url_read_seek;
}
(*s)-av_class = ff_avio_class;
   +(*s)-resizeable = 1;
return 0;
}

   diff --git a/libavformat/segment.c b/libavformat/segment.c
   index 1162ea2..6504b46 100644
   --- a/libavformat/segment.c
   +++ b/libavformat/segment.c
   @@ -511,6 +511,7 @@ static int open_null_ctx(AVIOContext **ctx)
av_free(buf);
return AVERROR(ENOMEM);
}
   +(*ctx)-resizeable = 1;
return 0;
}

   diff --git a/libavformat/wtvdec.c b/libavformat/wtvdec.c
   index e226690..7b5477b 100644
   --- a/libavformat/wtvdec.c
   +++ b/libavformat/wtvdec.c
   @@ -243,7 +243,8 @@ static AVIOContext * wtvfile_open_sector(int 
   first_sector, uint64_t length, int
av_freep(buffer);
av_freep(wf-sectors);
av_freep(wf);
   -}
   +} else
   +pb-resizeable = 1;
return pb;
}

  
  Looking at it again, ffio_ensure_seekback and ffio_set_buf_size are
  functions which resize the buffer (but by allocating a new buffer to
  avoid av_realloc incompatibility, as Nicolas pointed out).
  
 
  So what's the point of this patch?
 
 it intends to prevent memory bugs, like double frees, freeing
 randon addresses on the stack and things like that
 
 [...]

Downstream should be fixed (instead of adding such a hack to ffmpeg),
and custom IO should be made possible without forcing the user to do
the tricky buffer allocation. I think this would be ideal. Didn't check
yet why the user needs to allocate a buffer, or how it could be avoided.
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Re: [FFmpeg-devel] [PATCH 1/3] avformat/avio: add resizeable field to AVIOContext

2015-04-26 Thread Michael Niedermayer 
On Tue, Apr 21, 2015 at 02:23:19PM +0200, wm4 wrote:
 On Tue, 21 Apr 2015 13:22:00 +0200
 Michael Niedermayer michae...@gmx.at wrote:
 
  This indicates that its safe to use av_free/av_malloc on the IO context
  
  Signed-off-by: Michael Niedermayer michae...@gmx.at
  ---
   libavformat/avio.h|7 +++
   libavformat/aviobuf.c |1 +
   libavformat/segment.c |1 +
   libavformat/wtvdec.c  |3 ++-
   4 files changed, 11 insertions(+), 1 deletion(-)
  
  diff --git a/libavformat/avio.h b/libavformat/avio.h
  index 51913e3..73d1645 100644
  --- a/libavformat/avio.h
  +++ b/libavformat/avio.h
  @@ -196,6 +196,13 @@ typedef struct AVIOContext {
* This field is internal to libavformat and access from outside is 
  not allowed.
*/
   int orig_buffer_size;
  +
  +/**
  + * The io buffer can be resized or freed with av_free / av_malloc.
  + * The user application does not keep a private copy of the buffer 
  pointer
  + * which would become stale on such reallocation.
  + */
  +int resizeable;
   } AVIOContext;
   
   /* unbuffered I/O */
  diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
  index 7de59f1..b32ff9f 100644
  --- a/libavformat/aviobuf.c
  +++ b/libavformat/aviobuf.c
  @@ -793,6 +793,7 @@ int ffio_fdopen(AVIOContext **s, URLContext *h)
   (*s)-read_seek  = (int64_t (*)(void *, int, int64_t, 
  int))h-prot-url_read_seek;
   }
   (*s)-av_class = ff_avio_class;
  +(*s)-resizeable = 1;
   return 0;
   }
   
  diff --git a/libavformat/segment.c b/libavformat/segment.c
  index 1162ea2..6504b46 100644
  --- a/libavformat/segment.c
  +++ b/libavformat/segment.c
  @@ -511,6 +511,7 @@ static int open_null_ctx(AVIOContext **ctx)
   av_free(buf);
   return AVERROR(ENOMEM);
   }
  +(*ctx)-resizeable = 1;
   return 0;
   }
   
  diff --git a/libavformat/wtvdec.c b/libavformat/wtvdec.c
  index e226690..7b5477b 100644
  --- a/libavformat/wtvdec.c
  +++ b/libavformat/wtvdec.c
  @@ -243,7 +243,8 @@ static AVIOContext * wtvfile_open_sector(int 
  first_sector, uint64_t length, int
   av_freep(buffer);
   av_freep(wf-sectors);
   av_freep(wf);
  -}
  +} else
  +pb-resizeable = 1;
   return pb;
   }
   
 
 Looking at it again, ffio_ensure_seekback and ffio_set_buf_size are
 functions which resize the buffer (but by allocating a new buffer to
 avoid av_realloc incompatibility, as Nicolas pointed out).
 

 So what's the point of this patch?

it intends to prevent memory bugs, like double frees, freeing
randon addresses on the stack and things like that

[...]
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form of tyranny and slavery out of the most extreme liberty. -- Plato


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Re: [FFmpeg-devel] [PATCH 1/3] avformat/avio: add resizeable field to AVIOContext

2015-04-21 Thread Michael Niedermayer 
On Tue, Apr 21, 2015 at 02:03:43PM +0200, Nicolas George wrote:
 Le duodi 2 floréal, an CCXXIII, Michael Niedermayer a écrit :
  This indicates that its safe to use av_free/av_malloc on the IO context
  
  Signed-off-by: Michael Niedermayer michae...@gmx.at
  ---
   libavformat/avio.h|7 +++
   libavformat/aviobuf.c |1 +
   libavformat/segment.c |1 +
   libavformat/wtvdec.c  |3 ++-
   4 files changed, 11 insertions(+), 1 deletion(-)
  
  diff --git a/libavformat/avio.h b/libavformat/avio.h
  index 51913e3..73d1645 100644
  --- a/libavformat/avio.h
  +++ b/libavformat/avio.h
  @@ -196,6 +196,13 @@ typedef struct AVIOContext {
* This field is internal to libavformat and access from outside is 
  not allowed.
*/
   int orig_buffer_size;
  +
  +/**
  + * The io buffer can be resized or freed with av_free / av_malloc.
  + * The user application does not keep a private copy of the buffer 
  pointer
  + * which would become stale on such reallocation.
  + */
  +int resizeable;
 
 I suspect you should replace av_malloc() with av_realloc(). For example,

the API requires av_malloc(), this is documented in the
avio_alloc_context() doxy


 aviobuf.c uses av_realloc(); buffers created with av_malloc() can not
 officially be used with av_realloc().

[...]

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No human being will ever know the Truth, for even if they happen to say it
by chance, they would not even known they had done so. -- Xenophanes


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Re: [FFmpeg-devel] [PATCH 1/3] avformat/avio: add resizeable field to AVIOContext

2015-04-21 Thread Michael Niedermayer 
On Tue, Apr 21, 2015 at 02:41:15PM +0200, wm4 wrote:
 On Tue, 21 Apr 2015 14:37:36 +0200
 Michael Niedermayer michae...@gmx.at wrote:
 
  On Tue, Apr 21, 2015 at 01:52:05PM +0200, wm4 wrote:
   On Tue, 21 Apr 2015 13:22:00 +0200
   Michael Niedermayer michae...@gmx.at wrote:
   
This indicates that its safe to use av_free/av_malloc on the IO context

Signed-off-by: Michael Niedermayer michae...@gmx.at
---
 libavformat/avio.h|7 +++
 libavformat/aviobuf.c |1 +
 libavformat/segment.c |1 +
 libavformat/wtvdec.c  |3 ++-
 4 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/libavformat/avio.h b/libavformat/avio.h
index 51913e3..73d1645 100644
--- a/libavformat/avio.h
+++ b/libavformat/avio.h
@@ -196,6 +196,13 @@ typedef struct AVIOContext {
  * This field is internal to libavformat and access from outside 
is not allowed.
  */
 int orig_buffer_size;
+
+/**
+ * The io buffer can be resized or freed with av_free / av_malloc.
+ * The user application does not keep a private copy of the buffer 
pointer
+ * which would become stale on such reallocation.
+ */
+int resizeable;
 } AVIOContext;
 
 /* unbuffered I/O */
diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
index 7de59f1..b32ff9f 100644
--- a/libavformat/aviobuf.c
+++ b/libavformat/aviobuf.c
@@ -793,6 +793,7 @@ int ffio_fdopen(AVIOContext **s, URLContext *h)
 (*s)-read_seek  = (int64_t (*)(void *, int, int64_t, 
int))h-prot-url_read_seek;
 }
 (*s)-av_class = ff_avio_class;
+(*s)-resizeable = 1;
 return 0;
 }
 
diff --git a/libavformat/segment.c b/libavformat/segment.c
index 1162ea2..6504b46 100644
--- a/libavformat/segment.c
+++ b/libavformat/segment.c
@@ -511,6 +511,7 @@ static int open_null_ctx(AVIOContext **ctx)
 av_free(buf);
 return AVERROR(ENOMEM);
 }
+(*ctx)-resizeable = 1;
 return 0;
 }
 
diff --git a/libavformat/wtvdec.c b/libavformat/wtvdec.c
index e226690..7b5477b 100644
--- a/libavformat/wtvdec.c
+++ b/libavformat/wtvdec.c
@@ -243,7 +243,8 @@ static AVIOContext * wtvfile_open_sector(int 
first_sector, uint64_t length, int
 av_freep(buffer);
 av_freep(wf-sectors);
 av_freep(wf);
-}
+} else
+pb-resizeable = 1;
 return pb;
 }
 
   
   Isn't it already required by default that AVIOContext might resize the
   buffer?
  
  technically yes, but theres alot of code, well possibly most code
  using it that gets this wrong (videolan is one) and the consequences
  are rather bad (double free and such)
  so i think its better i we dont assume that the buffer can be resized
  by default
  
  [...]
  
 
 That comes a bit late. Wouldn't it be better to free the user from the
 responsibility of allocating this buffer entirely?

yes this was easily possible through the use of a custom URLProtocol
and as far as my oppinion is concerned, i do want URLProtocol and
all other things like AVFilters AVIn/OutputFormats, ... to be
creatable by user applications ...

Also simple user apps dont need to create the buffer anyway, ffmpeg*c
ffplay*c and most of our examples do not do. But that limits them
to the existing URLProtocols for IO which is a problem for many user
apps i think

[...]

-- 
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If a bugfix only changes things apparently unrelated to the bug with no
further explanation, that is a good sign that the bugfix is wrong.


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Re: [FFmpeg-devel] [PATCH 1/3] avformat/avio: add resizeable field to AVIOContext

2015-04-21 Thread wm4 
On Tue, 21 Apr 2015 14:37:36 +0200
Michael Niedermayer michae...@gmx.at wrote:

 On Tue, Apr 21, 2015 at 01:52:05PM +0200, wm4 wrote:
  On Tue, 21 Apr 2015 13:22:00 +0200
  Michael Niedermayer michae...@gmx.at wrote:
  
   This indicates that its safe to use av_free/av_malloc on the IO context
   
   Signed-off-by: Michael Niedermayer michae...@gmx.at
   ---
libavformat/avio.h|7 +++
libavformat/aviobuf.c |1 +
libavformat/segment.c |1 +
libavformat/wtvdec.c  |3 ++-
4 files changed, 11 insertions(+), 1 deletion(-)
   
   diff --git a/libavformat/avio.h b/libavformat/avio.h
   index 51913e3..73d1645 100644
   --- a/libavformat/avio.h
   +++ b/libavformat/avio.h
   @@ -196,6 +196,13 @@ typedef struct AVIOContext {
 * This field is internal to libavformat and access from outside is 
   not allowed.
 */
int orig_buffer_size;
   +
   +/**
   + * The io buffer can be resized or freed with av_free / av_malloc.
   + * The user application does not keep a private copy of the buffer 
   pointer
   + * which would become stale on such reallocation.
   + */
   +int resizeable;
} AVIOContext;

/* unbuffered I/O */
   diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
   index 7de59f1..b32ff9f 100644
   --- a/libavformat/aviobuf.c
   +++ b/libavformat/aviobuf.c
   @@ -793,6 +793,7 @@ int ffio_fdopen(AVIOContext **s, URLContext *h)
(*s)-read_seek  = (int64_t (*)(void *, int, int64_t, 
   int))h-prot-url_read_seek;
}
(*s)-av_class = ff_avio_class;
   +(*s)-resizeable = 1;
return 0;
}

   diff --git a/libavformat/segment.c b/libavformat/segment.c
   index 1162ea2..6504b46 100644
   --- a/libavformat/segment.c
   +++ b/libavformat/segment.c
   @@ -511,6 +511,7 @@ static int open_null_ctx(AVIOContext **ctx)
av_free(buf);
return AVERROR(ENOMEM);
}
   +(*ctx)-resizeable = 1;
return 0;
}

   diff --git a/libavformat/wtvdec.c b/libavformat/wtvdec.c
   index e226690..7b5477b 100644
   --- a/libavformat/wtvdec.c
   +++ b/libavformat/wtvdec.c
   @@ -243,7 +243,8 @@ static AVIOContext * wtvfile_open_sector(int 
   first_sector, uint64_t length, int
av_freep(buffer);
av_freep(wf-sectors);
av_freep(wf);
   -}
   +} else
   +pb-resizeable = 1;
return pb;
}

  
  Isn't it already required by default that AVIOContext might resize the
  buffer?
 
 technically yes, but theres alot of code, well possibly most code
 using it that gets this wrong (videolan is one) and the consequences
 are rather bad (double free and such)
 so i think its better i we dont assume that the buffer can be resized
 by default
 
 [...]
 

That comes a bit late. Wouldn't it be better to free the user from the
responsibility of allocating this buffer entirely?
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Re: [FFmpeg-devel] [PATCH 1/3] avformat/avio: add resizeable field to AVIOContext

2015-04-21 Thread Nicolas George 
Le duodi 2 floréal, an CCXXIII, Michael Niedermayer a écrit :
 This indicates that its safe to use av_free/av_malloc on the IO context
 
 Signed-off-by: Michael Niedermayer michae...@gmx.at
 ---
  libavformat/avio.h|7 +++
  libavformat/aviobuf.c |1 +
  libavformat/segment.c |1 +
  libavformat/wtvdec.c  |3 ++-
  4 files changed, 11 insertions(+), 1 deletion(-)
 
 diff --git a/libavformat/avio.h b/libavformat/avio.h
 index 51913e3..73d1645 100644
 --- a/libavformat/avio.h
 +++ b/libavformat/avio.h
 @@ -196,6 +196,13 @@ typedef struct AVIOContext {
   * This field is internal to libavformat and access from outside is not 
 allowed.
   */
  int orig_buffer_size;
 +
 +/**
 + * The io buffer can be resized or freed with av_free / av_malloc.
 + * The user application does not keep a private copy of the buffer 
 pointer
 + * which would become stale on such reallocation.
 + */
 +int resizeable;

I suspect you should replace av_malloc() with av_realloc(). For example,
aviobuf.c uses av_realloc(); buffers created with av_malloc() can not
officially be used with av_realloc().

Regards,

-- 
  Nicolas George


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Re: [FFmpeg-devel] [PATCH 1/3] avformat/avio: add resizeable field to AVIOContext

2015-04-21 Thread Michael Niedermayer 
On Tue, Apr 21, 2015 at 01:52:05PM +0200, wm4 wrote:
 On Tue, 21 Apr 2015 13:22:00 +0200
 Michael Niedermayer michae...@gmx.at wrote:
 
  This indicates that its safe to use av_free/av_malloc on the IO context
  
  Signed-off-by: Michael Niedermayer michae...@gmx.at
  ---
   libavformat/avio.h|7 +++
   libavformat/aviobuf.c |1 +
   libavformat/segment.c |1 +
   libavformat/wtvdec.c  |3 ++-
   4 files changed, 11 insertions(+), 1 deletion(-)
  
  diff --git a/libavformat/avio.h b/libavformat/avio.h
  index 51913e3..73d1645 100644
  --- a/libavformat/avio.h
  +++ b/libavformat/avio.h
  @@ -196,6 +196,13 @@ typedef struct AVIOContext {
* This field is internal to libavformat and access from outside is 
  not allowed.
*/
   int orig_buffer_size;
  +
  +/**
  + * The io buffer can be resized or freed with av_free / av_malloc.
  + * The user application does not keep a private copy of the buffer 
  pointer
  + * which would become stale on such reallocation.
  + */
  +int resizeable;
   } AVIOContext;
   
   /* unbuffered I/O */
  diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
  index 7de59f1..b32ff9f 100644
  --- a/libavformat/aviobuf.c
  +++ b/libavformat/aviobuf.c
  @@ -793,6 +793,7 @@ int ffio_fdopen(AVIOContext **s, URLContext *h)
   (*s)-read_seek  = (int64_t (*)(void *, int, int64_t, 
  int))h-prot-url_read_seek;
   }
   (*s)-av_class = ff_avio_class;
  +(*s)-resizeable = 1;
   return 0;
   }
   
  diff --git a/libavformat/segment.c b/libavformat/segment.c
  index 1162ea2..6504b46 100644
  --- a/libavformat/segment.c
  +++ b/libavformat/segment.c
  @@ -511,6 +511,7 @@ static int open_null_ctx(AVIOContext **ctx)
   av_free(buf);
   return AVERROR(ENOMEM);
   }
  +(*ctx)-resizeable = 1;
   return 0;
   }
   
  diff --git a/libavformat/wtvdec.c b/libavformat/wtvdec.c
  index e226690..7b5477b 100644
  --- a/libavformat/wtvdec.c
  +++ b/libavformat/wtvdec.c
  @@ -243,7 +243,8 @@ static AVIOContext * wtvfile_open_sector(int 
  first_sector, uint64_t length, int
   av_freep(buffer);
   av_freep(wf-sectors);
   av_freep(wf);
  -}
  +} else
  +pb-resizeable = 1;
   return pb;
   }
   
 
 Isn't it already required by default that AVIOContext might resize the
 buffer?

technically yes, but theres alot of code, well possibly most code
using it that gets this wrong (videolan is one) and the consequences
are rather bad (double free and such)
so i think its better i we dont assume that the buffer can be resized
by default

[...]

-- 
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

He who knows, does not speak. He who speaks, does not know. -- Lao Tsu


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[FFmpeg-devel] [PATCH 1/3] avformat/avio: add resizeable field to AVIOContext

2015-04-21 Thread Michael Niedermayer 
This indicates that its safe to use av_free/av_malloc on the IO context

Signed-off-by: Michael Niedermayer michae...@gmx.at
---
 libavformat/avio.h|7 +++
 libavformat/aviobuf.c |1 +
 libavformat/segment.c |1 +
 libavformat/wtvdec.c  |3 ++-
 4 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/libavformat/avio.h b/libavformat/avio.h
index 51913e3..73d1645 100644
--- a/libavformat/avio.h
+++ b/libavformat/avio.h
@@ -196,6 +196,13 @@ typedef struct AVIOContext {
  * This field is internal to libavformat and access from outside is not 
allowed.
  */
 int orig_buffer_size;
+
+/**
+ * The io buffer can be resized or freed with av_free / av_malloc.
+ * The user application does not keep a private copy of the buffer pointer
+ * which would become stale on such reallocation.
+ */
+int resizeable;
 } AVIOContext;
 
 /* unbuffered I/O */
diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
index 7de59f1..b32ff9f 100644
--- a/libavformat/aviobuf.c
+++ b/libavformat/aviobuf.c
@@ -793,6 +793,7 @@ int ffio_fdopen(AVIOContext **s, URLContext *h)
 (*s)-read_seek  = (int64_t (*)(void *, int, int64_t, 
int))h-prot-url_read_seek;
 }
 (*s)-av_class = ff_avio_class;
+(*s)-resizeable = 1;
 return 0;
 }
 
diff --git a/libavformat/segment.c b/libavformat/segment.c
index 1162ea2..6504b46 100644
--- a/libavformat/segment.c
+++ b/libavformat/segment.c
@@ -511,6 +511,7 @@ static int open_null_ctx(AVIOContext **ctx)
 av_free(buf);
 return AVERROR(ENOMEM);
 }
+(*ctx)-resizeable = 1;
 return 0;
 }
 
diff --git a/libavformat/wtvdec.c b/libavformat/wtvdec.c
index e226690..7b5477b 100644
--- a/libavformat/wtvdec.c
+++ b/libavformat/wtvdec.c
@@ -243,7 +243,8 @@ static AVIOContext * wtvfile_open_sector(int first_sector, 
uint64_t length, int
 av_freep(buffer);
 av_freep(wf-sectors);
 av_freep(wf);
-}
+} else
+pb-resizeable = 1;
 return pb;
 }
 
-- 
1.7.9.5

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Re: [FFmpeg-devel] [PATCH 1/3] avformat/avio: add resizeable field to AVIOContext

2015-04-21 Thread wm4 
On Tue, 21 Apr 2015 13:22:00 +0200
Michael Niedermayer michae...@gmx.at wrote:

 This indicates that its safe to use av_free/av_malloc on the IO context
 
 Signed-off-by: Michael Niedermayer michae...@gmx.at
 ---
  libavformat/avio.h|7 +++
  libavformat/aviobuf.c |1 +
  libavformat/segment.c |1 +
  libavformat/wtvdec.c  |3 ++-
  4 files changed, 11 insertions(+), 1 deletion(-)
 
 diff --git a/libavformat/avio.h b/libavformat/avio.h
 index 51913e3..73d1645 100644
 --- a/libavformat/avio.h
 +++ b/libavformat/avio.h
 @@ -196,6 +196,13 @@ typedef struct AVIOContext {
   * This field is internal to libavformat and access from outside is not 
 allowed.
   */
  int orig_buffer_size;
 +
 +/**
 + * The io buffer can be resized or freed with av_free / av_malloc.
 + * The user application does not keep a private copy of the buffer 
 pointer
 + * which would become stale on such reallocation.
 + */
 +int resizeable;
  } AVIOContext;
  
  /* unbuffered I/O */
 diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
 index 7de59f1..b32ff9f 100644
 --- a/libavformat/aviobuf.c
 +++ b/libavformat/aviobuf.c
 @@ -793,6 +793,7 @@ int ffio_fdopen(AVIOContext **s, URLContext *h)
  (*s)-read_seek  = (int64_t (*)(void *, int, int64_t, 
 int))h-prot-url_read_seek;
  }
  (*s)-av_class = ff_avio_class;
 +(*s)-resizeable = 1;
  return 0;
  }
  
 diff --git a/libavformat/segment.c b/libavformat/segment.c
 index 1162ea2..6504b46 100644
 --- a/libavformat/segment.c
 +++ b/libavformat/segment.c
 @@ -511,6 +511,7 @@ static int open_null_ctx(AVIOContext **ctx)
  av_free(buf);
  return AVERROR(ENOMEM);
  }
 +(*ctx)-resizeable = 1;
  return 0;
  }
  
 diff --git a/libavformat/wtvdec.c b/libavformat/wtvdec.c
 index e226690..7b5477b 100644
 --- a/libavformat/wtvdec.c
 +++ b/libavformat/wtvdec.c
 @@ -243,7 +243,8 @@ static AVIOContext * wtvfile_open_sector(int 
 first_sector, uint64_t length, int
  av_freep(buffer);
  av_freep(wf-sectors);
  av_freep(wf);
 -}
 +} else
 +pb-resizeable = 1;
  return pb;
  }
  

Isn't it already required by default that AVIOContext might resize the
buffer?
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