libavcodec/cbs: Stop needlessly reallocating the units array

Currently, a fragment's unit array is constantly reallocated during
splitting of a packet. This commit changes this: One can keep the units
array by distinguishing between the number of allocated and the number
of valid units in the units array.

The more units a packet is split into, the bigger the benefit.
So MPEG-2 benefits the most; for a video coming from an NTSC-DVD
(usually 32 units per frame) the average cost of cbs_insert_unit (for a
single unit) went down from 6717 decicycles to 450 decicycles (based
upon 10 runs with 4194304 runs each); if each packet consists of only
one unit, it went down from 2425 to 448; for a H.264 video where most
packets contain nine units, it went from 4431 to 450.

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

1 files changed, 3 insertions, 2 deletions

diff --git a/libavcodec/trace_headers_bsf.c b/libavcodec/trace_headers_bsf.c
index 61284e615e..3ec78fe822 100644
--- a/libavcodec/trace_headers_bsf.c
+++ b/libavcodec/trace_headers_bsf.c
@@ -51,7 +51,7 @@ static int trace_headers_init(AVBSFContext *bsf)
 
         err = ff_cbs_read_extradata(ctx->cbc, frag, bsf->par_in);
 
-        ff_cbs_fragment_uninit(ctx->cbc, frag);
+        ff_cbs_fragment_reset(ctx->cbc, frag);
     }
 
     return err;
@@ -61,6 +61,7 @@ static void trace_headers_close(AVBSFContext *bsf)
 {
     TraceHeadersContext *ctx = bsf->priv_data;
 
+    ff_cbs_fragment_free(ctx->cbc, &ctx->fragment);
     ff_cbs_close(&ctx->cbc);
 }
 
@@ -95,7 +96,7 @@ static int trace_headers(AVBSFContext *bsf, AVPacket *pkt)
 
     err = ff_cbs_read_packet(ctx->cbc, frag, pkt);
 
-    ff_cbs_fragment_uninit(ctx->cbc, frag);
+    ff_cbs_fragment_reset(ctx->cbc, frag);
 
     if (err < 0)
         av_packet_unref(pkt);