avformat: add option to parse/store ID3 PRIV tags in metadata.

Enables getting access to ID3 PRIV tags from the command-line or metadata API
when demuxing. The PRIV owner is stored as the metadata key prepended with
"id3v2_priv.", and the data is stored as the metadata value. As PRIV tags may
contain arbitrary data, non-printable characters, including NULL bytes, are
escaped as \xXX.

Similarly, any metadata tags that begin with "id3v2_priv." are inserted as ID3
PRIV tags into the output (assuming the format supports ID3). \xXX sequences in
the value are un-escaped to their byte value.

Signed-off-by: wm4 <nfxjfg@googlemail.com>

1 files changed, 60 insertions, 0 deletions

diff --git a/libavformat/id3v2enc.c b/libavformat/id3v2enc.c
index 14de76ac06..ffe358f019 100644
--- a/libavformat/id3v2enc.c
+++ b/libavformat/id3v2enc.c
@@ -96,6 +96,59 @@ static int id3v2_put_ttag(ID3v2EncContext *id3, AVIOContext *avioc, const char *
     return len + ID3v2_HEADER_SIZE;
 }
 
+/**
+ * Write a priv frame with owner and data. 'key' is the owner prepended with
+ * ID3v2_PRIV_METADATA_PREFIX. 'data' is provided as a string. Any \xXX
+ * (where 'X' is a valid hex digit) will be unescaped to the byte value.
+ */
+static int id3v2_put_priv(ID3v2EncContext *id3, AVIOContext *avioc, const char *key, const char *data)
+{
+    int len;
+    uint8_t *pb;
+    AVIOContext *dyn_buf;
+
+    if (!av_strstart(key, ID3v2_PRIV_METADATA_PREFIX, &key)) {
+        return 0;
+    }
+
+    if (avio_open_dyn_buf(&dyn_buf) < 0)
+        return AVERROR(ENOMEM);
+
+    // owner + null byte.
+    avio_write(dyn_buf, key, strlen(key) + 1);
+
+    while (*data) {
+        if (av_strstart(data, "\\x", &data)) {
+            if (data[0] && data[1] && av_isxdigit(data[0]) && av_isxdigit(data[1])) {
+                char digits[] = {data[0], data[1], 0};
+                avio_w8(dyn_buf, strtol(digits, NULL, 16));
+                data += 2;
+            } else {
+                ffio_free_dyn_buf(&dyn_buf);
+                av_log(avioc, AV_LOG_ERROR, "Invalid escape '\\x%.2s' in metadata tag '"
+                       ID3v2_PRIV_METADATA_PREFIX "%s'.\n", data, key);
+                return AVERROR(EINVAL);
+            }
+        } else {
+            avio_write(dyn_buf, data++, 1);
+        }
+    }
+
+    len = avio_close_dyn_buf(dyn_buf, &pb);
+
+    avio_wb32(avioc, MKBETAG('P', 'R', 'I', 'V'));
+    if (id3->version == 3)
+        avio_wb32(avioc, len);
+    else
+        id3v2_put_size(avioc, len);
+    avio_wb16(avioc, 0);
+    avio_write(avioc, pb, len);
+
+    av_free(pb);
+
+    return len + ID3v2_HEADER_SIZE;
+}
+
 static int id3v2_check_write_tag(ID3v2EncContext *id3, AVIOContext *pb, AVDictionaryEntry *t,
                                  const char table[][4], enum ID3v2Encoding enc)
 {
@@ -186,6 +239,13 @@ static int write_metadata(AVIOContext *pb, AVDictionary **metadata,
             continue;
         }
 
+        if ((ret = id3v2_put_priv(id3, pb, t->key, t->value)) > 0) {
+            id3->len += ret;
+            continue;
+        } else if (ret < 0) {
+            return ret;
+        }
+
         /* unknown tag, write as TXXX frame */
         if ((ret = id3v2_put_ttag(id3, pb, t->key, t->value, MKBETAG('T', 'X', 'X', 'X'), enc)) < 0)
             return ret;