This change is to add a tracklist for mp3-files on SD-Cards

[EFWob]

This change avoids time consuming reads of the nodelist at startup if contents of the SD cards have not changed. I employ this change for a "jukebox" for the grandparents. They usally listen to a few radiostations or have the favorite songs of their youth on one SD card. That card is never changed, so it is not needed to read the contents ever again.

Basic idea is as follows:

• if SD card is mounted, it is checked if a file called "/mp3tracks.txt" exists (name can be configured in "SDcard.h")
• if this file exists, it is considered valid, if the size is at least 11 and the first 11 chars contain sprintf("%10d=", SD_nodecount). Then SD_nodelist is expected to follow but as of now is not checked for consistency.
• if this file exists but is not valid by the above rule, it will be created and filled with valid information on next start of the radio.
• if this file does not exists, radio will behave as usual (read the SD card at start)

So, if you fill or update an SD-Card, you need to create an empty "/mp3tracks.txt" to be filled at first start of the radio, or delete "/mp3track.txt" to make the radio behave as usual.

This can be also done from command line: "tracklist=delete" deletes tracklist (if existing) "tracklist=init" created an empty tracklist to be filled at next start (if not existing already, will prompt to delete first).

Issues will arise, if contents of the SD card a(mp3 files) are changed and the tracklist is not deleted/emptied!

[EFWob]

The diff is bigger than the actual change is: Currently, there is a #define TRACKLIST defined in the first line of SDcard.h

All other changes are guarded by that define:

• two global variables are declared in line 11 and 12 of SDcard.h
• function setup_SDCARD() has been altered at lines 469ff
• function analyzeCmd() has been altered in Esp32_radio.ino lines 5039ff

Sorry for the confusion.

[utw3v0]

is it possible to call the textfile as well when clicking on mp3player so instead of reading the whole sd card read the textfile ? or maybe copy the content into a buffer and refresh from there ? i also had a wired view in the tracklist so i had to change the lines @ 234 from p = file.name() + ldirname ; to SD_outbuf += tmpstr + // Form line for mp3play_html page utf8ascii ( file.name() + ldirname ) + // Filename String ( "\n" ) ; to get a full file list