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>
(cherry picked from commit 7c92eaace2b338e0b3acc18e1543b365610578fd)

1 files changed, 4 insertions, 58 deletions

diff --git a/libavcodec/cbs_mpeg2.c b/libavcodec/cbs_mpeg2.c
index cb202f835b..a49a403b26 100644
--- a/libavcodec/cbs_mpeg2.c
+++ b/libavcodec/cbs_mpeg2.c
@@ -335,58 +335,13 @@ static int cbs_mpeg2_write_slice(CodedBitstreamContext *ctx,
 }
 
 static int cbs_mpeg2_write_unit(CodedBitstreamContext *ctx,
-                                CodedBitstreamUnit *unit)
+                                CodedBitstreamUnit *unit,
+                                PutBitContext *pbc)
 {
-    CodedBitstreamMPEG2Context *priv = ctx->priv_data;
-    PutBitContext pbc;
-    int err;
-
-    if (!priv->write_buffer) {
-        // Initial write buffer size is 1MB.
-        priv->write_buffer_size = 1024 * 1024;
-
-    reallocate_and_try_again:
-        err = av_reallocp(&priv->write_buffer, priv->write_buffer_size);
-        if (err < 0) {
-            av_log(ctx->log_ctx, AV_LOG_ERROR, "Unable to allocate a "
-                   "sufficiently large write buffer (last attempt "
-                   "%"SIZE_SPECIFIER" bytes).\n", priv->write_buffer_size);
-            return err;
-        }
-    }
-
-    init_put_bits(&pbc, priv->write_buffer, priv->write_buffer_size);
-
     if (MPEG2_START_IS_SLICE(unit->type))
-        err = cbs_mpeg2_write_slice(ctx, unit, &pbc);
-    else
-        err = cbs_mpeg2_write_header(ctx, unit, &pbc);
-
-    if (err == AVERROR(ENOSPC)) {
-        // Overflow.
-        priv->write_buffer_size *= 2;
-        goto reallocate_and_try_again;
-    }
-    if (err < 0) {
-        // Write failed for some other reason.
-        return err;
-    }
-
-    if (put_bits_count(&pbc) % 8)
-        unit->data_bit_padding = 8 - put_bits_count(&pbc) % 8;
+        return cbs_mpeg2_write_slice (ctx, unit, pbc);
     else
-        unit->data_bit_padding = 0;
-
-    unit->data_size = (put_bits_count(&pbc) + 7) / 8;
-    flush_put_bits(&pbc);
-
-    err = ff_cbs_alloc_unit_data(ctx, unit, unit->data_size);
-    if (err < 0)
-        return err;
-
-    memcpy(unit->data, priv->write_buffer, unit->data_size);
-
-    return 0;
+        return cbs_mpeg2_write_header(ctx, unit, pbc);
 }
 
 static int cbs_mpeg2_assemble_fragment(CodedBitstreamContext *ctx,
@@ -426,13 +381,6 @@ static int cbs_mpeg2_assemble_fragment(CodedBitstreamContext *ctx,
     return 0;
 }
 
-static void cbs_mpeg2_close(CodedBitstreamContext *ctx)
-{
-    CodedBitstreamMPEG2Context *priv = ctx->priv_data;
-
-    av_freep(&priv->write_buffer);
-}
-
 const CodedBitstreamType ff_cbs_type_mpeg2 = {
     .codec_id          = AV_CODEC_ID_MPEG2VIDEO,
 
@@ -442,6 +390,4 @@ const CodedBitstreamType ff_cbs_type_mpeg2 = {
     .read_unit         = &cbs_mpeg2_read_unit,
     .write_unit        = &cbs_mpeg2_write_unit,
     .assemble_fragment = &cbs_mpeg2_assemble_fragment,
-
-    .close             = &cbs_mpeg2_close,
 };