Fix SaizBox truncate sizing for default sample info entries

[p-bond]

Fix SaizBox truncate sizing for default sample info layouts

SaizBox::truncate assumed every SAIZ box had a per-sample info table and always reduced the box size by sample_count - 1 when truncating to one sample. That is only valid when default_sample_info_size is zero. For boxes that use a non-zero default sample info size, there is no per-sample table to shrink, so the old logic could write an invalid smaller size and corrupt the rewritten buffer.

This change preserves whether a per-sample table is present when parsing SAIZ and only shrinks the box when that table exists. It also returns early for sample counts of 0 or 1 to avoid invalid size arithmetic.

The L1 IsoBmffBoxTests suite now covers the table-present path, the default-size path where size must stay unchanged, and the low-sample guard behavior.

[Copilot]

Pull request overview

Fixes SaizBox::truncate() sizing when SAIZ uses a non-zero default_sample_info_size (i.e., no per-sample info table to shrink), preventing invalid box-size writes that can corrupt rewritten ISO BMFF buffers.

Changes:

• Track whether SAIZ parsing encountered a per-sample info size table and only shrink the SAIZ box when that table exists.
• Add an early return in SaizBox::truncate() for numSamples <= 1 to avoid invalid size arithmetic.
• Expand IsoBmffBoxTests coverage for SAIZ: table-present vs default-size layouts and low-sample guard behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
isobmff/isobmffbox.cpp	Preserve SAIZ layout details during parsing and conditionally shrink size during truncate.
isobmff/isobmffbox.h	Extend SaizBox state and constructor signature to carry “table present” info.
test/utests/tests/IsoBmffBoxTests/IsoBmffBoxTests.cpp	Add L1 tests validating SAIZ truncation behavior across SAIZ layouts and sample counts.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

isobmff/isobmffbox.cpp:1690

• SaizBox::truncate() now falls into the else branch (and logs "No room for a skip box") whenever hasPerSampleInfoTable is false, because oldSize == newSize makes (oldSize - newSize) >= SIZEOF_SIZE_AND_TAG false. For default-sample-info-size SAIZ boxes, this log is misleading (there was no truncation attempt and room is irrelevant) and could add noise in normal playback.

	// Need min 8 bytes to insert a skip box
	if ((oldSize - newSize) >= SIZEOF_SIZE_AND_TAG)
	{
		WRITE_U32(getBase(), newSize);
		SkipBox skip{oldSize - newSize, getBase() + newSize};
	}
	else
	{
		AAMPLOG_INFO("No room for a skip box");
		// Not truncating the table, just setting the sample count to 1
	}