mpeg2: 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_mpeg2.c b/gst-libs/gst/vaapi/gstvaapidecoder_mpeg2.c
index 7ecd9d19c31110047f3f56520725d50e5cf71c4f..1624dd8fbb41156b4fb40a87aa295f39224784b6 100644 (file)
--- a/gst-libs/gst/vaapi/gstvaapidecoder_mpeg2.c
+++ b/gst-libs/gst/vaapi/gstvaapidecoder_mpeg2.c
@@ -1160,13 +1160,14 @@ gst_vaapi_decoder_mpeg2_parse(GstVaapiDecoder *base_decoder,
 {
     GstVaapiDecoderMpeg2 * const decoder =
         GST_VAAPI_DECODER_MPEG2(base_decoder);
+    GstVaapiParserState * const ps = GST_VAAPI_PARSER_STATE(base_decoder);
     GstVaapiDecoderUnitMpeg2 *unit;
     GstVaapiDecoderStatus status;
     GstMpegVideoPacket *packet;
     const guchar *buf;
     guint32 start_code;
     guint size, buf_size, flags;
-    gint ofs;
+    gint ofs, ofs2;
 
     status = ensure_decoder(decoder);
     if (status != GST_VAAPI_DECODER_STATUS_SUCCESS)
@@ -1179,18 +1180,28 @@ gst_vaapi_decoder_mpeg2_parse(GstVaapiDecoder *base_decoder,
     ofs = scan_for_start_code(adapter, 0, size, &start_code);
     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 packet 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 = gst_adapter_peek(adapter, buf_size);
     if (!buf)