fix(mp4): Use fixed-width integer types in bswap functions

Change bswap16 and bswap32 to use int16_t and int32_t instead of
short and long for consistent behavior across platforms.

On Windows x64, `long` is 4 bytes (LLP64 model), while on Linux x64
`long` is 8 bytes (LP64 model). This difference could cause
inconsistent NAL unit length parsing in MP4/MOV files, potentially
affecting timestamp calculations.

This fix ensures the byte-swapping functions work identically on
both platforms by using fixed-width integer types from <stdint.h>.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: cfsmp3

src/lib_ccx/mp4.c

@@ -31,15 +31,17 @@
 #define GF_ISOM_SUBTYPE_MPEG4 GF_4CC('M', 'P', 'E', 'G')
 #endif
 
-static short bswap16(short v)
+static int16_t bswap16(int16_t v)
 {
 	return ((v >> 8) & 0x00FF) | ((v << 8) & 0xFF00);
 }
 
-static long bswap32(long v)
+static int32_t bswap32(int32_t v)
 {
 	// For 0x12345678 returns 78563412
-	long swapped = ((v & 0xFF) << 24) | ((v & 0xFF00) << 8) | ((v & 0xFF0000) >> 8) | ((v & 0xFF000000) >> 24);
+	// Use int32_t instead of long for consistent behavior across platforms
+	// (long is 4 bytes on Windows x64 but 8 bytes on Linux x64)
+	int32_t swapped = ((v & 0xFF) << 24) | ((v & 0xFF00) << 8) | ((v & 0xFF0000) >> 8) | ((v & 0xFF000000) >> 24);
 	return swapped;
 }
 static struct
@@ -82,10 +84,10 @@ static int process_avc_sample(struct lib_ccx_ctx *ctx, u32 timescale, GF_AVCConf
 				nal_length = s->data[i];
 				break;
 			case 2:
-				nal_length = bswap16(*(short *)&s->data[i]);
+				nal_length = bswap16(*(int16_t *)&s->data[i]);
 				break;
 			case 4:
-				nal_length = bswap32(*(long *)&s->data[i]);
+				nal_length = bswap32(*(int32_t *)&s->data[i]);
 				break;
 		}
 		const u32 previous_index = i;
@@ -151,10 +153,10 @@ static int process_hevc_sample(struct lib_ccx_ctx *ctx, u32 timescale, GF_HEVCCo
 				nal_length = s->data[i];
 				break;
 			case 2:
-				nal_length = bswap16(*(short *)&s->data[i]);
+				nal_length = bswap16(*(int16_t *)&s->data[i]);
 				break;
 			case 4:
-				nal_length = bswap32(*(long *)&s->data[i]);
+				nal_length = bswap32(*(int32_t *)&s->data[i]);
 				break;
 			default:
 				mprint("Unexpected nal_unit_size %u in HEVC config\n", c->nal_unit_size);