Fix compilation on FFmpeg7?

Author: NicolasHug

src/torchcodec/_core/AVIOBytesContext.cpp

@@ -73,7 +73,7 @@ AVIOToTensorContext::AVIOToTensorContext()
 }
 
 // The signature of this function is defined by FFMPEG.
-int AVIOToTensorContext::write(void* opaque, uint8_t* buf, int buf_size) {
+int AVIOToTensorContext::write(void* opaque, const uint8_t* buf, int buf_size) {
   auto dataContext = static_cast<DataContext*>(opaque);
 
   if (dataContext->current + buf_size > dataContext->outputTensor.numel()) {

src/torchcodec/_core/AVIOBytesContext.h

@@ -44,7 +44,7 @@ class AVIOToTensorContext : public AVIOContextHolder {
 
   static const int INITIAL_TENSOR_SIZE = 10'000'000; // 10MB
   static const int MAX_TENSOR_SIZE = 320'000'000; // 320 MB
-  static int write(void* opaque, uint8_t* buf, int buf_size);
+  static int write(void* opaque, const uint8_t* buf, int buf_size);
   // We need to expose seek() for some formats like mp3.
   static int64_t seek(void* opaque, int64_t offset, int whence);
 

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(avio_alloc_context(
+  avioContext_.reset(AVIOAllocContext(
       buffer,
       bufferSize,
       /*write_flag=*/write != nullptr,

src/torchcodec/_core/AVIOContextHolder.h

@@ -46,7 +46,7 @@ class AVIOContextHolder {
 
   // These signatures are defined by FFmpeg.
   using AVIOReadFunction = int (*)(void*, uint8_t*, int);
-  using AVIOWriteFunction = 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.

src/torchcodec/_core/FFMPEGCommon.cpp

@@ -261,4 +261,27 @@ void setFFmpegLogLevel() {
   av_log_set_level(logLevel);
 }
 
+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)) {
+  return avio_alloc_context(
+      buffer,
+      buffer_size,
+      write_flag,
+      opaque,
+      read_packet,
+// The buf parameter of the write function is not const before FFmpeg 7.
+#if LIBAVFILTER_VERSION_MAJOR >= 10 // FFmpeg >= 7
+      write_packet,
+#else
+      reinterpret_cast<int (*)(void*, uint8_t*, int)>(write_packet),
+#endif
+      seek);
+}
+
 } // namespace facebook::torchcodec

src/torchcodec/_core/FFMPEGCommon.h

@@ -177,4 +177,13 @@ bool canSwsScaleHandleUnalignedData();
 
 void setFFmpegLogLevel();
 
+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));
+
 } // namespace facebook::torchcodec