avcodec/cbs: Factor out common code for writing units

All cbs-functions to write units share a common pattern:
1. They check whether they have a write buffer (that is used to store
the unit's data until the needed size becomes known after writing the
unit when a dedicated buffer will be allocated).
2. They use this buffer for a PutBitContext.
3. The (codec-specific) writing takes place through the PutBitContext.
4. The return value is checked. AVERROR(ENOSPC) here always indicates
that the buffer was too small and leads to a reallocation of said
buffer.
5. The final buffer will be allocated and the data copied.

This commit factors this common code out in a single function in cbs.c.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/libavcodec/cbs_internal.h b/libavcodec/cbs_internal.h
index dd4babf092..4c5a535ca6 100644
--- a/libavcodec/cbs_internal.h
+++ b/libavcodec/cbs_internal.h
@@ -44,9 +44,11 @@ typedef struct CodedBitstreamType {
     int (*read_unit)(CodedBitstreamContext *ctx,
                      CodedBitstreamUnit *unit);
 
-    // Write the unit->data bitstream from unit->content.
+    // Write the data bitstream from unit->content into pbc.
+    // Return value AVERROR(ENOSPC) indicates that pbc was too small.
     int (*write_unit)(CodedBitstreamContext *ctx,
-                      CodedBitstreamUnit *unit);
+                      CodedBitstreamUnit *unit,
+                      PutBitContext *pbc);
 
     // Read the data from all of frag->units and assemble it into
     // a bitstream for the whole fragment.