1 files changed, 81 insertions, 0 deletions
diff --git a/libavformat/mux_utils.c b/libavformat/mux_utils.c
new file mode 100644
index 0000000000..7b79ffd1fb
--- /dev/null
+++ b/libavformat/mux_utils.c
@@ -0,0 +1,81 @@
+/*
+ * Various muxing utility functions
+ * Copyright (c) 2000, 2001, 2002 Fabrice Bellard
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "avformat.h"
+#include "avio.h"
+#include "internal.h"
+#include "mux.h"
+
+int ff_format_shift_data(AVFormatContext *s, int64_t read_start, int shift_size)
+{
+    int ret;
+    int64_t pos, pos_end;
+    uint8_t *buf, *read_buf[2];
+    int read_buf_id = 0;
+    int read_size[2];
+    AVIOContext *read_pb;
+
+    buf = av_malloc_array(shift_size, 2);
+    if (!buf)
+        return AVERROR(ENOMEM);
+    read_buf[0] = buf;
+    read_buf[1] = buf + shift_size;
+
+    /* Shift the data: the AVIO context of the output can only be used for
+     * writing, so we re-open the same output, but for reading. It also avoids
+     * a read/seek/write/seek back and forth. */
+    avio_flush(s->pb);
+    ret = s->io_open(s, &read_pb, s->url, AVIO_FLAG_READ, NULL);
+    if (ret < 0) {
+        av_log(s, AV_LOG_ERROR, "Unable to re-open %s output file for shifting data\n", s->url);
+        goto end;
+    }
+
+    /* mark the end of the shift to up to the last data we wrote, and get ready
+     * for writing */
+    pos_end = avio_tell(s->pb);
+    avio_seek(s->pb, read_start + shift_size, SEEK_SET);
+
+    avio_seek(read_pb, read_start, SEEK_SET);
+    pos = avio_tell(read_pb);
+
+#define READ_BLOCK do {                                                             \
+    read_size[read_buf_id] = avio_read(read_pb, read_buf[read_buf_id], shift_size);  \
+    read_buf_id ^= 1;                                                               \
+} while (0)
+
+    /* shift data by chunk of at most shift_size */
+    READ_BLOCK;
+    do {
+        int n;
+        READ_BLOCK;
+        n = read_size[read_buf_id];
+        if (n <= 0)
+            break;
+        avio_write(s->pb, read_buf[read_buf_id], n);
+        pos += n;
+    } while (pos < pos_end);
+    ret = ff_format_io_close(s, &read_pb);
+
+end:
+    av_free(buf);
+    return ret;
+}