utils: cplay: Add support for ID3v2 tag skip

This patch will allow playing MP3 files containing ID3v2
tag at the beginning of the file.

This is done simply by parsing the ID3v2 header, extracting
the header size and seeking to that position (+10 bytes
from the header size which is not included in the 'header
size' field of the ID3v2 header)

Signed-off-by: Laurentiu Mihalcea <laurentiu.mihalcea@nxp.com>

diff --git a/src/utils/cplay.c b/src/utils/cplay.c
index 790408b67d0e01ef1d058f08faea5306e629efd9..3afe681591ce19cf7437da99014750b50732f6f3 100644 (file)
--- a/src/utils/cplay.c
+++ b/src/utils/cplay.c
@@ -76,6 +76,9 @@
 #include "tinycompress/tinymp3.h"
 #include "tinycompress/tinywave.h"
 
+#define ID3V2_HEADER_SIZE 10
+#define ID3V2_FILE_IDENTIFIER_SIZE 3
+
 enum {
        DO_NOTHING = -1,
        DO_PAUSE_PUSH,
@@ -599,12 +602,94 @@ void get_codec_aac(FILE *file, struct compr_config *config,
        codec->format = format;
 }
 
+static int skip_id3v2_header(FILE *file)
+{
+       char buffer[ID3V2_HEADER_SIZE + 1];
+       int ret, bytes_read;
+       uint32_t header_size;
+
+       /* we only need to parse ID3v2 header in order to skip
+        * the whole ID3v2 tag found at the beginning of the file.
+        *
+        * ID3v2 header has the following structure(v2.3.0):
+        *
+        * 1) file identifier
+        *      => 3 bytes long.
+        *      => has the value of ID3 for ID3v2 tag.
+        *
+        * 2) version
+        *      => 2 bytes long.
+        *
+        * 3) flags
+        *      => 1 byte long.
+        *
+        * 4) size
+        *      => 4 bytes long.
+        *      => the MSB of each byte is 0 so it needs to be ignored
+        *      when trying to parse the size.
+        *      => this field doesn't include the 10 bytes which make up
+        *      the ID3v2 header so a +10 needs to be added to this
+        *      field in order to get the correct position of the end
+        *      of the ID3v2 tag.
+        */
+
+       /* for now, we only support ID3v2 header found at the beginning
+        * of the file so we need to move file cursor to the beginning
+        * of the file
+        */
+       ret = fseek(file, 0, SEEK_SET);
+       if (ret < 0)
+               return ret;
+
+       buffer[ID3V2_HEADER_SIZE] = '\0';
+
+       /* read first ID3V2_HEADER_SIZE chunk */
+       bytes_read = fread(buffer, sizeof(char), ID3V2_HEADER_SIZE, file);
+
+       /* ID3v2 header is 10 bytes long
+        *
+        * if we can't read the 10 bytes then there's obviously no
+        * ID3v2 tag to skip
+        */
+       if (bytes_read != ID3V2_HEADER_SIZE)
+               return 0;
+
+       /* check if we're dealing with ID3v2 */
+       if (strncmp(buffer, "ID3", ID3V2_FILE_IDENTIFIER_SIZE) != 0)
+               return 0;
+
+       header_size = buffer[9];
+       header_size |= (buffer[8] << 7);
+       header_size |= (buffer[7] << 14);
+       header_size |= (buffer[6] << 21);
+
+       /* the header size field in ID3v2 header doesn't
+        * include the 10 bytes of which the header is made
+        * so we need to add them to get the correct position
+        */
+       return header_size + ID3V2_HEADER_SIZE;
+}
+
 void get_codec_mp3(FILE *file, struct compr_config *config,
                struct snd_codec *codec)
 {
        size_t read;
        struct mp3_header header;
        unsigned int channels, rate, bits;
+       int offset;
+
+       offset = skip_id3v2_header(file);
+       if (offset < 0) {
+               fprintf(stderr, "Failed to get ID3 tag end position.\n");
+               fclose(file);
+               exit(EXIT_FAILURE);
+       }
+
+       if (fseek(file, offset, SEEK_SET) < 0) {
+               fprintf(stderr, "Unable to seek.\n");
+               fclose(file);
+               exit(EXIT_FAILURE);
+       }
 
        read = fread(&header, 1, sizeof(header), file);
        if (read != sizeof(header)) {
@@ -634,7 +719,7 @@ void get_codec_mp3(FILE *file, struct compr_config *config,
        codec->ch_mode = 0;
        codec->format = 0;
 
-       /* reset file cursor to start
+       /* reset file cursor to offset position
         *
         * this is done because if we leave it as is
         * the program will hang in a poll call waiting
@@ -648,8 +733,8 @@ void get_codec_mp3(FILE *file, struct compr_config *config,
         * likely hang because it's expecting to also get
         * the MP3 header
         */
-       if (fseek(file, 0, SEEK_SET) < 0) {
-               fprintf(stderr, "Failed to set cursor to start.\n");
+       if (fseek(file, offset, SEEK_SET) < 0) {
+               fprintf(stderr, "Failed to set cursor to offset.\n");
                fclose(file);
                exit(EXIT_FAILURE);
        }