[FFmpeg-devel] [PATCH v2] utvideoenc: Enable support for multiple slices and use them

[Jan Ekström]

The official Ut Video decoder only threads with slices, thus until
now any files encoded by the libavcodec encoder have only been
decodable with a single thread. The default slice count is now
set to subsampled_height / 120.

Also sets slices to 1 for the Ut Video encoder tests to keep them
green.
---
 libavcodec/utvideoenc.c | 37 ++++++++++++++++++++++++++++++++++---
 tests/fate/utvideo.mak  |  2 +-
 2 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/libavcodec/utvideoenc.c b/libavcodec/utvideoenc.c
index ab2cfaa..494d2e1 100644
--- a/libavcodec/utvideoenc.c
+++ b/libavcodec/utvideoenc.c
@@ -58,7 +58,7 @@ static av_cold int utvideo_encode_close(AVCodecContext *avctx)
 static av_cold int utvideo_encode_init(AVCodecContext *avctx)
 {
     UtvideoContext *c = avctx->priv_data;
-    int i;
+    int i, subsampled_height;
     uint32_t original_format;
 
     c->avctx           = avctx;
@@ -132,6 +132,26 @@ static av_cold int utvideo_encode_init(AVCodecContext *avctx)
         return AVERROR_OPTION_NOT_FOUND;
     }
 
+    /*
+     * Check the asked slice count for obviously invalid
+     * values (> 256 or negative).
+     */
+    if (avctx->slices > 256 || avctx->slices < 0) {
+        av_log(avctx, AV_LOG_ERROR,
+               "Slice count %d is not supported in Ut Video (theoretical range is 0-256).\n",
+               avctx->slices);
+        return AVERROR(EINVAL);
+    }
+
+    /* Check that the slice count is not larger than the subsampled height */
+    subsampled_height = avctx->height >> av_pix_fmt_desc_get(avctx->pix_fmt)->log2_chroma_h;
+    if (avctx->slices > subsampled_height) {
+        av_log(avctx, AV_LOG_ERROR,
+               "Slice count %d is larger than the subsampling-applied height %d.\n",
+               avctx->slices, subsampled_height);
+        return AVERROR(EINVAL);
+    }
+
     avctx->coded_frame = av_frame_alloc();
 
     if (!avctx->coded_frame) {
@@ -181,9 +201,20 @@ static av_cold int utvideo_encode_init(AVCodecContext *avctx)
 
     /*
      * Set how many slices are going to be used.
-     * Set one slice for now.
+     * By default uses multiple slices depending on the subsampled height.
+     * This enables multithreading in the official decoder.
      */
-    c->slices = 1;
+    if (!avctx->slices) {
+        c->slices = subsampled_height / 120;
+
+        if (!c->slices) {
+            c->slices = 1;
+        } else if (c->slices > 256) {
+            c->slices = 256;
+        }
+    } else {
+        c->slices = avctx->slices;
+    }
 
     /* Set compression mode */
     c->compression = COMP_HUFF;
diff --git a/tests/fate/utvideo.mak b/tests/fate/utvideo.mak
index 6ec206b..1e4755e 100644
--- a/tests/fate/utvideo.mak
+++ b/tests/fate/utvideo.mak
@@ -28,7 +28,7 @@ fate-utvideo_yuv422_median: CMD = framecrc -i $(TARGET_SAMPLES)/utvideo/utvideo_
 FATE_SAMPLES_AVCONV-$(call DEMDEC, AVI, UTVIDEO) += $(FATE_UTVIDEO)
 fate-utvideo: $(FATE_UTVIDEO)
 
-fate-utvideoenc%: CMD = framemd5 -f image2 -vcodec pgmyuv -i $(TARGET_PATH)/tests/vsynth1/%02d.pgm -vcodec utvideo -sws_flags +accurate_rnd+bitexact ${OPTS}
+fate-utvideoenc%: CMD = framemd5 -f image2 -vcodec pgmyuv -i $(TARGET_PATH)/tests/vsynth1/%02d.pgm -vcodec utvideo -slices 1 -sws_flags +accurate_rnd+bitexact ${OPTS}
 
 FATE_UTVIDEOENC += fate-utvideoenc_rgba_left
 fate-utvideoenc_rgba_left: OPTS = -pix_fmt rgba -pred left
-- 
1.8.5.4