Null buffers are useful for simulating writing to a real buffer
for the sake of measuring how many bytes are written.
---
In practice this doesn't reduce the IO work completely, since
the data still is written to the intermediate IO buffer, but it
does avoid having to allocate the output buffer and copy data
into it, and simplifies the code a little for the callers.
---
libavformat/avio_internal.h | 18 ++++++++++++++++++
libavformat/aviobuf.c | 33 +++++++++++++++++++++++++++++++++
2 files changed, 51 insertions(+)
diff --git a/libavformat/avio_internal.h b/libavformat/avio_internal.h
index 5493163..e3367c8 100644
--- a/libavformat/avio_internal.h
+++ b/libavformat/avio_internal.h
@@ -119,4 +119,22 @@ int ffio_open_dyn_packet_buf(AVIOContext **s, int
max_packet_size);
*/
int ffio_fdopen(AVIOContext **s, URLContext *h);
+/**
+ * Open a write only fake memory stream. The written data isn't stored
+ * anywhere - this is only used for measuring the amount of data
+ * written.
+ *
+ * @param s new IO context
+ * @return zero if no error.
+ */
+int ffio_open_null_buf(AVIOContext **s);
+
+/**
+ * Close a null buffer.
+ *
+ * @param s an IO context opened by ffio_open_null_buf
+ * @return the number of bytes written to the null buffer
+ */
+int ffio_close_null_buf(AVIOContext *s);
+
#endif /* AVFORMAT_AVIO_INTERNAL_H */
diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
index 7d76e0b..3f27d69 100644
--- a/libavformat/aviobuf.c
+++ b/libavformat/aviobuf.c
@@ -975,3 +975,36 @@ int avio_close_dyn_buf(AVIOContext *s, uint8_t **pbuffer)
av_free(s);
return size - padding;
}
+
+static int null_buf_write(void *opaque, uint8_t *buf, int buf_size)
+{
+ DynBuffer *d = opaque;
+
+ d->pos += buf_size;
+ if (d->pos > d->size)
+ d->size = d->pos;
+ return buf_size;
+}
+
+int ffio_open_null_buf(AVIOContext **s)
+{
+ int ret = url_open_dyn_buf_internal(s, 0);
+ if (ret >= 0) {
+ AVIOContext *pb = *s;
+ pb->write_packet = null_buf_write;
+ }
+ return ret;
+}
+
+int ffio_close_null_buf(AVIOContext *s)
+{
+ DynBuffer *d = s->opaque;
+ int size;
+
+ avio_flush(s);
+
+ size = d->size;
+ av_free(d);
+ av_free(s);
+ return size;
+}
--
1.7.9.4
_______________________________________________
libav-devel mailing list
[email protected]
https://lists.libav.org/mailman/listinfo/libav-devel
