mmaldec: disable timestamp interpolation

This MMAL feature fills in missing timestamps from the framerate set on
the input port. This is generally unwanted, since libavcodec decoders
merely pass through timestamps without ever "fixing" them. The framerate
is also unknown, and even the timebase doesn't have to be set.
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

libavcodec/mmaldec.c

@@ -26,6 +26,7 @@
 
 #include <bcm_host.h>
 #include <interface/mmal/mmal.h>
+#include <interface/mmal/mmal_parameters_video.h>
 #include <interface/mmal/util/mmal_util.h>
 #include <interface/mmal/util/mmal_util_params.h>
 #include <interface/mmal/util/mmal_default_components.h>
@@ -277,6 +278,9 @@ static int ffmal_update_format(AVCodecContext *avctx)
     if ((status = mmal_port_parameter_set_uint32(decoder->output[0], MMAL_PARAMETER_EXTRA_BUFFERS, ctx->extra_buffers)))
         goto fail;
 
+    if ((status = mmal_port_parameter_set_boolean(decoder->output[0], MMAL_PARAMETER_VIDEO_INTERPOLATE_TIMESTAMPS, 0)))
+        goto fail;
+
     if (avctx->pix_fmt == AV_PIX_FMT_MMAL) {
         format_out->encoding = MMAL_ENCODING_OPAQUE;
     } else {