mmaldec: limit internal buffering

This uses a new MMAL feature, which limits the number of extra frames
that can be buffered within the decoder. VIDEO_MAX_NUM_CALLBACKS can
be defined as positive or negative number. Positive numbers are
absolute, and can lead to deadlocks if the user underestimates the
number of required buffers. Negative numbers specify the number of extra
buffers, e.g. -1 means no extra buffer, (-1-N) means N extra buffers.

Set a gratuitous default of -11 (N=10). This is much lower than the
firmware default, which appears to be 96.

This is backwards compatible, but needs a symbol only present in newer
firmware headers. (It's an enum item, so it requires a check in
configure.)

diff --git a/configure b/configure
index 60c940273484be9834692a242584fb73273b1d73..629029ebe4f032e8fe5d0ce8942a7fb031c9c5e7 100755 (executable)
--- a/configure
+++ b/configure
@@ -5579,6 +5579,10 @@ enabled mmal              && { check_lib interface/mmal/mmal.h mmal_port_connect
                                     check_lib interface/mmal/mmal.h mmal_port_connect ; }
                                 check_lib interface/mmal/mmal.h mmal_port_connect ; } ||
                                die "ERROR: mmal not found"; }
+enabled mmal &&
+    (check_code cc interface/mmal/mmal.h "MMAL_PARAMETER_VIDEO_MAX_NUM_CALLBACKS" ||
+     die "ERROR: mmal firmware headers too old")
+
 enabled netcdf            && require_pkg_config netcdf netcdf.h nc_inq_libvers
 enabled nvenc             && { check_header nvEncodeAPI.h || die "ERROR: nvEncodeAPI.h not found."; } &&
                              { check_cpp_condition nvEncodeAPI.h "NVENCAPI_MAJOR_VERSION >= 5" ||

diff --git a/libavcodec/mmaldec.c b/libavcodec/mmaldec.c
index ed633948b4e05f80ceb882ce7dab9eef1ffed7fd..30861d9bcf210b84f76696c96c2eda9d21be530c 100644 (file)
--- a/libavcodec/mmaldec.c
+++ b/libavcodec/mmaldec.c
@@ -66,6 +66,7 @@ typedef struct FFBufferRef {
 typedef struct MMALDecodeContext {
     AVClass *av_class;
     int extra_buffers;
+    int extra_decoder_buffers;
 
     MMAL_COMPONENT_T *decoder;
     MMAL_QUEUE_T *queue_decoded_frames;
@@ -382,6 +383,11 @@ static av_cold int ffmmal_init_decoder(AVCodecContext *avctx)
     av_get_codec_tag_string(tmp, sizeof(tmp), format_in->encoding);
     av_log(avctx, AV_LOG_DEBUG, "Using MMAL %s encoding.\n", tmp);
 
+    if (mmal_port_parameter_set_uint32(decoder->input[0], MMAL_PARAMETER_VIDEO_MAX_NUM_CALLBACKS,
+                                       -1 - ctx->extra_decoder_buffers)) {
+        av_log(avctx, AV_LOG_WARNING, "Could not set input buffering limit.\n");
+    }
+
     if ((status = mmal_port_format_commit(decoder->input[0])))
         goto fail;
 
@@ -812,6 +818,7 @@ AVHWAccel ff_vc1_mmal_hwaccel = {
 
 static const AVOption options[]={
     {"extra_buffers", "extra buffers", offsetof(MMALDecodeContext, extra_buffers), AV_OPT_TYPE_INT, {.i64 = 10}, 0, 256, 0},
+    {"extra_decoder_buffers", "extra MMAL internal buffered frames", offsetof(MMALDecodeContext, extra_decoder_buffers), AV_OPT_TYPE_INT, {.i64 = 10}, 0, 256, 0},
     {NULL}
 };