cbs: Don't set AVBuffer's opaque

cbs is currently inconsistent regarding the opaque field that can be
used as a special argument to av_buffer_create in order to be used
during freeing the buffer: ff_cbs_alloc_unit_content and all the free
functions used name this parameter as if it should contain a pointer to
the unit whose content is about to be created; but both
ff_cbs_alloc_unit_content as well as ff_cbs_h264_add_sei_message
actually use a pointer to the CodedBitstreamContext as opaque. It should
actually be neither, because it is unneeded (as is evidenced by the fact
that none of the free functions use this pointer at all) and because it
ties the unit's content to the lifetime of other objects, although a
refcounted buffer is supposed to have its own lifetime that only ends
when its reference count reaches zero. This problem manifests itself in
the pointer becoming dangling.
The pointer to the unit can become dangling if another unit is added to
the fragment later as happens in the bitstream filters; in this case,
the pointer can point to the wrong unit (if the fragment's unit array
needn't be relocated) or it can point to where the array was earlier.
It can also become dangling if the unit's content is meant to survive
the resetting of the fragment it was originally read with. This applies
to the extradata of H.264 and HEVC.
The pointer to the context can become dangling if the context is closed
before the content is freed. Although this doesn't seem to happen right
now, it could happen, in particular if one uses different
CodedBitstreamContexts for in- and output.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/cbs.c

@@ -597,7 +597,7 @@ int ff_cbs_alloc_unit_content(CodedBitstreamContext *ctx,
         return AVERROR(ENOMEM);
 
     unit->content_ref = av_buffer_create(unit->content, size,
-                                         free, ctx, 0);
+                                         free, NULL, 0);
     if (!unit->content_ref) {
         av_freep(&unit->content);
         return AVERROR(ENOMEM);

libavcodec/cbs.h

@@ -341,7 +341,7 @@ void ff_cbs_fragment_free(CodedBitstreamContext *ctx,
 int ff_cbs_alloc_unit_content(CodedBitstreamContext *ctx,
                               CodedBitstreamUnit *unit,
                               size_t size,
-                              void (*free)(void *unit, uint8_t *content));
+                              void (*free)(void *opaque, uint8_t *content));
 
 /**
  * Allocate a new internal data buffer of the given size in the unit.

libavcodec/cbs_av1.c

@@ -829,7 +829,7 @@ static void cbs_av1_free_metadata(AV1RawMetadata *md)
     }
 }
 
-static void cbs_av1_free_obu(void *unit, uint8_t *content)
+static void cbs_av1_free_obu(void *opaque, uint8_t *content)
 {
     AV1RawOBU *obu = (AV1RawOBU*)content;
 

libavcodec/cbs_h2645.c

@@ -443,7 +443,7 @@ static int cbs_h2645_read_more_rbsp_data(GetBitContext *gbc)
 #undef allocate
 
 
-static void cbs_h264_free_pps(void *unit, uint8_t *content)
+static void cbs_h264_free_pps(void *opaque, uint8_t *content)
 {
     H264RawPPS *pps = (H264RawPPS*)content;
     av_buffer_unref(&pps->slice_group_id_ref);
@@ -473,7 +473,7 @@ static void cbs_h264_free_sei_payload(H264RawSEIPayload *payload)
     }
 }
 
-static void cbs_h264_free_sei(void *unit, uint8_t *content)
+static void cbs_h264_free_sei(void *opaque, uint8_t *content)
 {
     H264RawSEI *sei = (H264RawSEI*)content;
     int i;
@@ -482,35 +482,35 @@ static void cbs_h264_free_sei(void *unit, uint8_t *content)
     av_freep(&content);
 }
 
-static void cbs_h264_free_slice(void *unit, uint8_t *content)
+static void cbs_h264_free_slice(void *opaque, uint8_t *content)
 {
     H264RawSlice *slice = (H264RawSlice*)content;
     av_buffer_unref(&slice->data_ref);
     av_freep(&content);
 }
 
-static void cbs_h265_free_vps(void *unit, uint8_t *content)
+static void cbs_h265_free_vps(void *opaque, uint8_t *content)
 {
     H265RawVPS *vps = (H265RawVPS*)content;
     av_buffer_unref(&vps->extension_data.data_ref);
     av_freep(&content);
 }
 
-static void cbs_h265_free_sps(void *unit, uint8_t *content)
+static void cbs_h265_free_sps(void *opaque, uint8_t *content)
 {
     H265RawSPS *sps = (H265RawSPS*)content;
     av_buffer_unref(&sps->extension_data.data_ref);
     av_freep(&content);
 }
 
-static void cbs_h265_free_pps(void *unit, uint8_t *content)
+static void cbs_h265_free_pps(void *opaque, uint8_t *content)
 {
     H265RawPPS *pps = (H265RawPPS*)content;
     av_buffer_unref(&pps->extension_data.data_ref);
     av_freep(&content);
 }
 
-static void cbs_h265_free_slice(void *unit, uint8_t *content)
+static void cbs_h265_free_slice(void *opaque, uint8_t *content)
 {
     H265RawSlice *slice = (H265RawSlice*)content;
     av_buffer_unref(&slice->data_ref);
@@ -545,7 +545,7 @@ static void cbs_h265_free_sei_payload(H265RawSEIPayload *payload)
     }
 }
 
-static void cbs_h265_free_sei(void *unit, uint8_t *content)
+static void cbs_h265_free_sei(void *opaque, uint8_t *content)
 {
     H265RawSEI *sei = (H265RawSEI*)content;
     int i;
@@ -1615,7 +1615,7 @@ int ff_cbs_h264_add_sei_message(CodedBitstreamContext *ctx,
         sei->nal_unit_header.nal_ref_idc   = 0;
 
         sei_ref = av_buffer_create((uint8_t*)sei, sizeof(*sei),
-                                   &cbs_h264_free_sei, ctx, 0);
+                                   &cbs_h264_free_sei, NULL, 0);
         if (!sei_ref) {
             av_freep(&sei);
             return AVERROR(ENOMEM);

libavcodec/cbs_jpeg.c

@@ -82,21 +82,21 @@
 #undef xu
 
 
-static void cbs_jpeg_free_application_data(void *unit, uint8_t *content)
+static void cbs_jpeg_free_application_data(void *opaque, uint8_t *content)
 {
     JPEGRawApplicationData *ad = (JPEGRawApplicationData*)content;
     av_buffer_unref(&ad->Ap_ref);
     av_freep(&content);
 }
 
-static void cbs_jpeg_free_comment(void *unit, uint8_t *content)
+static void cbs_jpeg_free_comment(void *opaque, uint8_t *content)
 {
     JPEGRawComment *comment = (JPEGRawComment*)content;
     av_buffer_unref(&comment->Cm_ref);
     av_freep(&content);
 }
 
-static void cbs_jpeg_free_scan(void *unit, uint8_t *content)
+static void cbs_jpeg_free_scan(void *opaque, uint8_t *content)
 {
     JPEGRawScan *scan = (JPEGRawScan*)content;
     av_buffer_unref(&scan->data_ref);

libavcodec/cbs_mpeg2.c

@@ -140,21 +140,21 @@
 #undef infer
 
 
-static void cbs_mpeg2_free_picture_header(void *unit, uint8_t *content)
+static void cbs_mpeg2_free_picture_header(void *opaque, uint8_t *content)
 {
     MPEG2RawPictureHeader *picture = (MPEG2RawPictureHeader*)content;
     av_buffer_unref(&picture->extra_information_picture.extra_information_ref);
     av_freep(&content);
 }
 
-static void cbs_mpeg2_free_user_data(void *unit, uint8_t *content)
+static void cbs_mpeg2_free_user_data(void *opaque, uint8_t *content)
 {
     MPEG2RawUserData *user = (MPEG2RawUserData*)content;
     av_buffer_unref(&user->user_data_ref);
     av_freep(&content);
 }
 
-static void cbs_mpeg2_free_slice(void *unit, uint8_t *content)
+static void cbs_mpeg2_free_slice(void *opaque, uint8_t *content)
 {
     MPEG2RawSlice *slice = (MPEG2RawSlice*)content;
     av_buffer_unref(&slice->header.extra_information_slice.extra_information_ref);

libavcodec/cbs_vp9.c

@@ -474,7 +474,7 @@ static int cbs_vp9_split_fragment(CodedBitstreamContext *ctx,
     return 0;
 }
 
-static void cbs_vp9_free_frame(void *unit, uint8_t *content)
+static void cbs_vp9_free_frame(void *opaque, uint8_t *content)
 {
     VP9RawFrame *frame = (VP9RawFrame*)content;
     av_buffer_unref(&frame->data_ref);