avformat/aviobuf: Add function to reset dynamic buffer

Resetting a dynamic buffer means to keep the AVIOContext and the
internal buffer used by the dynamic buffer. This is done in order to
save (re)allocations when one has a workflow where one opens and closes
dynamic buffers in sequence.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/avio_internal.h

@@ -171,6 +171,13 @@ int ffio_open_whitelist(AVIOContext **s, const char *url, int flags,
  */
 int ffio_close_null_buf(AVIOContext *s);
 
+/**
+ * Reset a dynamic buffer.
+ *
+ * Resets everything, but keeps the allocated buffer for later use.
+ */
+void ffio_reset_dyn_buf(AVIOContext *s);
+
 /**
  * Free a dynamic buffer.
  *

libavformat/aviobuf.c

@@ -1407,6 +1407,17 @@ int avio_get_dyn_buf(AVIOContext *s, uint8_t **pbuffer)
     return d->size;
 }
 
+void ffio_reset_dyn_buf(AVIOContext *s)
+{
+    DynBuffer *d = s->opaque;
+    int max_packet_size = s->max_packet_size;
+
+    ffio_init_context(s, d->io_buffer, d->io_buffer_size, 1, d, NULL,
+                      s->write_packet, s->seek);
+    s->max_packet_size = max_packet_size;
+    d->pos = d->size = 0;
+}
+
 int avio_close_dyn_buf(AVIOContext *s, uint8_t **pbuffer)
 {
     DynBuffer *d;