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>

libavformat/id3v2.c

@@ -33,6 +33,7 @@
 #endif
 
 #include "libavutil/avstring.h"
+#include "libavutil/bprint.h"
 #include "libavutil/dict.h"
 #include "libavutil/intreadwrite.h"
 #include "avio_internal.h"
@@ -1224,3 +1225,50 @@ end:
     av_freep(&chapters);
     return ret;
 }
+
+int ff_id3v2_parse_priv_dict(AVDictionary **metadata, ID3v2ExtraMeta **extra_meta)
+{
+    ID3v2ExtraMeta *cur;
+    int dict_flags = AV_DICT_DONT_OVERWRITE | AV_DICT_DONT_STRDUP_KEY | AV_DICT_DONT_STRDUP_VAL;
+
+    for (cur = *extra_meta; cur; cur = cur->next) {
+        if (!strcmp(cur->tag, "PRIV")) {
+            ID3v2ExtraMetaPRIV *priv = cur->data;
+            AVBPrint bprint;
+            char *escaped, *key;
+            int i, ret;
+
+            if ((key = av_asprintf(ID3v2_PRIV_METADATA_PREFIX "%s", priv->owner)) == NULL) {
+                return AVERROR(ENOMEM);
+            }
+
+            av_bprint_init(&bprint, priv->datasize + 1, AV_BPRINT_SIZE_UNLIMITED);
+
+            for (i = 0; i < priv->datasize; i++) {
+                if (priv->data[i] < 32 || priv->data[i] > 126 || priv->data[i] == '\\') {
+                    av_bprintf(&bprint, "\\x%02x", priv->data[i]);
+                } else {
+                    av_bprint_chars(&bprint, priv->data[i], 1);
+                }
+            }
+
+            if ((ret = av_bprint_finalize(&bprint, &escaped)) < 0) {
+                av_free(key);
+                return ret;
+            }
+
+            if ((ret = av_dict_set(metadata, key, escaped, dict_flags)) < 0) {
+                av_free(key);
+                av_free(escaped);
+                return ret;
+            }
+        }
+    }
+
+    return 0;
+}
+
+int ff_id3v2_parse_priv(AVFormatContext *s, ID3v2ExtraMeta **extra_meta)
+{
+    return ff_id3v2_parse_priv_dict(&s->metadata, extra_meta);
+}

libavformat/id3v2.h

@@ -39,6 +39,8 @@
 #define ID3v2_FLAG_ENCRYPTION  0x0004
 #define ID3v2_FLAG_COMPRESSION 0x0008
 
+#define ID3v2_PRIV_METADATA_PREFIX "id3v2_priv."
+
 enum ID3v2Encoding {
     ID3v2_ENCODING_ISO8859  = 0,
     ID3v2_ENCODING_UTF16BOM = 1,
@@ -167,6 +169,19 @@ int ff_id3v2_parse_apic(AVFormatContext *s, ID3v2ExtraMeta **extra_meta);
  */
 int ff_id3v2_parse_chapters(AVFormatContext *s, ID3v2ExtraMeta **extra_meta);
 
+/**
+ * Parse PRIV tags into a dictionary. The PRIV owner is the metadata key. The
+ * PRIV data is the value, with non-printable characters escaped.
+ */
+int ff_id3v2_parse_priv_dict(AVDictionary **d, ID3v2ExtraMeta **extra_meta);
+
+/**
+ * Add metadata for all PRIV tags in the ID3v2 header. The PRIV owner is the
+ * metadata key. The PRIV data is the value, with non-printable characters
+ * escaped.
+ */
+int ff_id3v2_parse_priv(AVFormatContext *s, ID3v2ExtraMeta **extra_meta);
+
 extern const AVMetadataConv ff_id3v2_34_metadata_conv[];
 extern const AVMetadataConv ff_id3v2_4_metadata_conv[];
 

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;

libavformat/utils.c

@@ -637,6 +637,8 @@ int avformat_open_input(AVFormatContext **ps, const char *filename,
                 goto fail;
             if ((ret = ff_id3v2_parse_chapters(s, &id3v2_extra_meta)) < 0)
                 goto fail;
+            if ((ret = ff_id3v2_parse_priv(s, &id3v2_extra_meta)) < 0)
+                goto fail;
         } else
             av_log(s, AV_LOG_DEBUG, "demuxer does not support additional id3 data, skipping\n");
     }

libavformat/version.h

@@ -33,7 +33,7 @@
 // Also please add any ticket numbers that you believe might be affected here
 #define LIBAVFORMAT_VERSION_MAJOR  58
 #define LIBAVFORMAT_VERSION_MINOR   5
-#define LIBAVFORMAT_VERSION_MICRO 100
+#define LIBAVFORMAT_VERSION_MICRO 101
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \