Move type aliases, fix avioAllocContext name

Author: NicolasHug

src/torchcodec/_core/AVIOContextHolder.cpp

@@ -27,7 +27,7 @@ void AVIOContextHolder::createAVIOContext(
       (seek != nullptr) && ((write != nullptr) ^ (read != nullptr)),
       "seek method must be defined, and either write or read must be defined. "
       "But not both!")
-  avioContext_.reset(AVIOAllocContext(
+  avioContext_.reset(avioAllocContext(
       buffer,
       bufferSize,
       /*write_flag=*/write != nullptr,

src/torchcodec/_core/AVIOContextHolder.h

@@ -44,11 +44,6 @@ class AVIOContextHolder {
   // enforced by having a pure virtual methods, but we don't have any.)
   AVIOContextHolder() = default;
 
-  // These signatures are defined by FFmpeg.
-  using AVIOReadFunction = int (*)(void*, uint8_t*, int);
-  using AVIOWriteFunction = int (*)(void*, const uint8_t*, int);
-  using AVIOSeekFunction = int64_t (*)(void*, int64_t, int);
-
   // Deriving classes should call this function in their constructor.
   void createAVIOContext(
       AVIOReadFunction read,

src/torchcodec/_core/FFMPEGCommon.cpp

@@ -261,14 +261,14 @@ void setFFmpegLogLevel() {
   av_log_set_level(logLevel);
 }
 
-AVIOContext* AVIOAllocContext(
+AVIOContext* avioAllocContext(
     uint8_t* buffer,
     int buffer_size,
     int write_flag,
     void* opaque,
-    int (*read_packet)(void* opaque, uint8_t* buf, int buf_size),
-    int (*write_packet)(void* opaque, const uint8_t* buf, int buf_size),
-    int64_t (*seek)(void* opaque, int64_t offset, int whence)) {
+    AVIOReadFunction read_packet,
+    AVIOWriteFunction write_packet,
+    AVIOSeekFunction seek) {
   return avio_alloc_context(
       buffer,
       buffer_size,
@@ -279,7 +279,7 @@ AVIOContext* AVIOAllocContext(
 #if LIBAVFILTER_VERSION_MAJOR >= 10 // FFmpeg >= 7
       write_packet,
 #else
-      reinterpret_cast<int (*)(void*, uint8_t*, int)>(write_packet),
+      reinterpret_cast<AVIOWriteFunctionOld>(write_packet),
 #endif
       seek);
 }

src/torchcodec/_core/FFMPEGCommon.h

@@ -177,13 +177,19 @@ bool canSwsScaleHandleUnalignedData();
 
 void setFFmpegLogLevel();
 
-AVIOContext* AVIOAllocContext(
+// These signatures are defined by FFmpeg.
+using AVIOReadFunction = int (*)(void*, uint8_t*, int);
+using AVIOWriteFunction = int (*)(void*, const uint8_t*, int); // FFmpeg >= 7
+using AVIOWriteFunctionOld = int (*)(void*, uint8_t*, int); // FFmpeg < 7
+using AVIOSeekFunction = int64_t (*)(void*, int64_t, int);
+
+AVIOContext* avioAllocContext(
     uint8_t* buffer,
     int buffer_size,
     int write_flag,
     void* opaque,
-    int (*read_packet)(void* opaque, uint8_t* buf, int buf_size),
-    int (*write_packet)(void* opaque, const uint8_t* buf, int buf_size),
-    int64_t (*seek)(void* opaque, int64_t offset, int whence));
+    AVIOReadFunction read_packet,
+    AVIOWriteFunction write_packet,
+    AVIOSeekFunction seek);
 
 } // namespace facebook::torchcodec