avformat/iamf_parse: fix setting duration for the last subblock in a parameter definition

When subblock durations are constant, the last block may be smaller and the
value needs to be calculated.

Signed-off-by: James Almer <jamrial@gmail.com>
(cherry picked from commit fb5e8ea971)

libavformat/iamf_parse.c

@@ -534,7 +534,8 @@ static int param_parse(void *s, IAMFContext *c, AVIOContext *pb,
         if (constant_subblock_duration == 0) {
             subblock_duration = ffio_read_leb(pb);
             total_duration += subblock_duration;
-        }
+        } else if (i == nb_subblocks - 1)
+            subblock_duration = duration - i * constant_subblock_duration;
 
         switch (type) {
         case AV_IAMF_PARAMETER_DEFINITION_MIX_GAIN: {

libavformat/iamf_reader.c

@@ -178,7 +178,8 @@ static int parameter_block_obu(AVFormatContext *s, IAMFDemuxContext *c,
         if (!param_definition->mode && !constant_subblock_duration) {
             subblock_duration = ffio_read_leb(pb);
             total_duration += subblock_duration;
-        }
+        } else if (i == nb_subblocks - 1)
+            subblock_duration = duration - i * constant_subblock_duration;
 
         switch (param->type) {
         case AV_IAMF_PARAMETER_DEFINITION_MIX_GAIN: {