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 7ecd9d1..1624dd8 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)