h264: optimize scan for the second start code.

Optimize scan for the second start code, on the next parse() call so that
to avoid scanning again earlier bytes where we didn't find any start code.

diff --git a/gst-libs/gst/vaapi/gstvaapidecoder_h264.c b/gst-libs/gst/vaapi/gstvaapidecoder_h264.c
index 6b36c84..af57d20 100644 (file)
--- a/gst-libs/gst/vaapi/gstvaapidecoder_h264.c
+++ b/gst-libs/gst/vaapi/gstvaapidecoder_h264.c
@@ -2982,13 +2982,14 @@ gst_vaapi_decoder_h264_parse(GstVaapiDecoder *base_decoder,
 {
     GstVaapiDecoderH264 * const decoder = GST_VAAPI_DECODER_H264(base_decoder);
     GstVaapiDecoderH264Private * const priv = decoder->priv;
+    GstVaapiParserState * const ps = GST_VAAPI_PARSER_STATE(base_decoder);
     GstVaapiDecoderUnitH264 *unit;
     GstVaapiDecoderStatus status;
     GstH264ParserResult result;
     guchar *buf;
     guint i, size, buf_size, nalu_size, flags;
     guint32 start_code;
-    gint ofs;
+    gint ofs, ofs2;
 
     status = ensure_decoder(decoder);
     if (status != GST_VAAPI_DECODER_STATUS_SUCCESS)
@@ -3015,22 +3016,33 @@ gst_vaapi_decoder_h264_parse(GstVaapiDecoder *base_decoder,
     else {
         if (size < 4)
             return GST_VAAPI_DECODER_STATUS_ERROR_NO_DATA;
+
         ofs = scan_for_start_code(adapter, 0, size, NULL);
         if (ofs < 0)
             return GST_VAAPI_DECODER_STATUS_ERROR_NO_DATA;
-        gst_adapter_flush(adapter, ofs);
-        size -= ofs;
 
-        ofs = G_UNLIKELY(size < 8) ? -1 :
-            scan_for_start_code(adapter, 4, size - 4, NULL);
+        if (ofs > 0) {
+            gst_adapter_flush(adapter, ofs);
+            size -= ofs;
+        }
+
+        ofs2 = ps->input_offset2 - ofs - 4;
+        if (ofs2 < 4)
+            ofs2 = 4;
+
+        ofs = G_UNLIKELY(size < ofs2 + 4) ? -1 :
+            scan_for_start_code(adapter, ofs2, size - ofs2, NULL);
         if (ofs < 0) {
             // Assume the whole NAL unit is present if end-of-stream
-            if (!at_eos)
+            if (!at_eos) {
+                ps->input_offset2 = size;
                 return GST_VAAPI_DECODER_STATUS_ERROR_NO_DATA;
+            }
             ofs = size;
         }
         buf_size = ofs;
     }
+    ps->input_offset2 = 0;
 
     buf = (guchar *)gst_adapter_peek(adapter, buf_size);
     if (!buf)