Hello!
I am trying to create a custom AVIOContext so that I can "catch" the output of
FFmpeg and direct it where I need it (not a file). I have done this
successfully to the point of generating a playable video file (which I am
sending to a file during development, but won't later.) After the file is
generated, however, I run into memory cleanup problems in avio_close(). The
crash occurs even if I immediately call avio_close() after
avio_alloc_context(), and I think I have an idea why:
I am passing an 'opaque' pointer to the avio_alloc_context() / AVIOContext
which points back to my redirecting class/object so that my callback functions
know where their object lives. This certainly appears to work for me, so I was
assuming that was the purpose of 'opaque', and I have it pointing to my own
object type.
However, when I look at the source code in aviobuf.c, avio_close(), we have:
int avio_close(AVIOContext *s){ URLContext *h = s->opaque;
av_free(s->buffer); av_free(s); return ffurl_close(h);}
Note that opaque is expected to have type 'URLContext *'. I tracked my memory
crash to the ffurl_close() line, so:
int ffurl_close(URLContext *h){ int ret = 0; if (!h) return 0; /* can
happen when ffurl_open fails */
if (h->is_connected && h->prot->url_close) ret =
h->prot->url_close(h);#if CONFIG_NETWORK ff_network_close();#endif if
(h->prot->priv_data_size) av_free(h->priv_data); av_free(h);
return ret;}
And my problem becomes rather obvious - AVIOContext->opaque is expected to
point to a structure of type URLContext for this close routine, not to a custom
type to be passed in to my callback routines. The code crashes when it tries
to access h->prot, although all of the ffurl_close() will be problematic unless
h (which is AVIOContext->opaque) references a URLContext structure.
I have no idea what the url_open(), ffurl_...(), etc. routines are used for,
and can't think of any reason that I need them in my project. However, I do
need the opaque pointer sent to my callback routines.
A workaround would be to avoid calling avio_close() and instead call av_free()
directly on the buffer and AVIOContext. However, before I resort to a
workaround, I wanted to check my understanding of the situation against people
more familiar with FFmpeg's code? Can you guys please verify or correct my
interpretation of the matter?
Thanks,Wiley
_______________________________________________
Libav-user mailing list
[email protected]
http://ffmpeg.org/mailman/listinfo/libav-user
