avformat/dashdec: drop arbitrary DASH manifest size limit

Currently the utilized AVBPrint API is internally limited to unsigned
integers, so if we limit the file size as well as the amount to read
to UINT_MAX - 1, we do not require additional limiting to be performed
on the values.

This change is based on the fact that initially the 8*1024 value added
in 96d70694ae was only for the case where
the file size was not known. It was not a maximum file size limit.

In 2912118898 this was reworked to be
a maximum manifest file size limit, while its commit message appears
to only note that it added support for larger manifest file sizes.

This should enable various unfortunately large MPEG-DASH manifests,
such as Youtube's multi-megabyte live stream archives to load up
as well as bring back the original intent of the logic.

libavformat/dashdec.c

@@ -29,7 +29,7 @@
 #include "dash.h"
 
 #define INITIAL_BUFFER_SIZE 32768
-#define MAX_MANIFEST_SIZE 50 * 1024
+#define MAX_BPRINT_READ_SIZE (UINT_MAX - 1)
 #define DEFAULT_MANIFEST_SIZE 8 * 1024
 
 struct fragment {
@@ -1256,14 +1256,16 @@ static int parse_manifest(AVFormatContext *s, const char *url, AVIOContext *in)
     }
 
     filesize = avio_size(in);
-    if (filesize > MAX_MANIFEST_SIZE) {
+    filesize = filesize > 0 ? filesize : DEFAULT_MANIFEST_SIZE;
+
+    if (filesize > MAX_BPRINT_READ_SIZE) {
         av_log(s, AV_LOG_ERROR, "Manifest too large: %"PRId64"\n", filesize);
         return AVERROR_INVALIDDATA;
     }
 
-    av_bprint_init(&buf, (filesize > 0) ? filesize + 1 : DEFAULT_MANIFEST_SIZE, AV_BPRINT_SIZE_UNLIMITED);
+    av_bprint_init(&buf, filesize + 1, AV_BPRINT_SIZE_UNLIMITED);
 
-    if ((ret = avio_read_to_bprint(in, &buf, MAX_MANIFEST_SIZE)) < 0 ||
+    if ((ret = avio_read_to_bprint(in, &buf, MAX_BPRINT_READ_SIZE)) < 0 ||
         !avio_feof(in) ||
         (filesize = buf.len) == 0) {
         av_log(s, AV_LOG_ERROR, "Unable to read to manifest '%s'\n", url);