avcodec/amfenc: Implement async_depth option

This option, which is also available on other FFmpeg hardware encoders,
allows the user to trade throughput for reduced output latency. This is
useful for ultra low latency applications like game streaming.

Signed-off-by: Cameron Gutman <aicommander@gmail.com>

libavcodec/amfenc.c

@@ -274,7 +274,6 @@ static int amf_init_context(AVCodecContext *avctx)
     av_unused int ret;
 
     ctx->hwsurfaces_in_queue = 0;
-    ctx->hwsurfaces_in_queue_max = 16;
 
     // configure AMF logger
     // the return of these functions indicates old state and do not affect behaviour
@@ -329,7 +328,7 @@ static int amf_init_context(AVCodecContext *avctx)
             return AVERROR(ENOMEM);
 
         if (frames_ctx->initial_pool_size > 0)
-            ctx->hwsurfaces_in_queue_max = frames_ctx->initial_pool_size - 1;
+            ctx->hwsurfaces_in_queue_max = FFMIN(ctx->hwsurfaces_in_queue_max, frames_ctx->initial_pool_size - 1);
 
     } else if (avctx->hw_device_ctx) {
         AVHWDeviceContext *device_ctx = (AVHWDeviceContext*)avctx->hw_device_ctx->data;

libavcodec/amfenc_av1.c

@@ -97,6 +97,8 @@ static const AVOption options[] = {
     { "gop",                    "", 0, AV_OPT_TYPE_CONST, {.i64 = AMF_VIDEO_ENCODER_AV1_HEADER_INSERTION_MODE_GOP_ALIGNED       }, 0, 0, VE, .unit = "hdrmode" },
     { "frame",                  "", 0, AV_OPT_TYPE_CONST, {.i64 = AMF_VIDEO_ENCODER_AV1_HEADER_INSERTION_MODE_KEY_FRAME_ALIGNED }, 0, 0, VE, .unit = "hdrmode" },
 
+    { "async_depth",            "Set maximum encoding parallelism. Higher values increase output latency.", OFFSET(hwsurfaces_in_queue_max), AV_OPT_TYPE_INT, {.i64 = 16 }, 1, 16, VE },
+
     { "preencode",              "Enable preencode",     OFFSET(preencode),      AV_OPT_TYPE_BOOL, {.i64 = -1  }, -1, 1, VE},
     { "enforce_hrd",            "Enforce HRD",          OFFSET(enforce_hrd),    AV_OPT_TYPE_BOOL, {.i64 = -1  }, -1, 1, VE},
     { "filler_data",            "Filler Data Enable",   OFFSET(filler_data),    AV_OPT_TYPE_BOOL, {.i64 = -1  }, -1, 1, VE},

libavcodec/amfenc_h264.c

@@ -110,6 +110,9 @@ static const AVOption options[] = {
     /// Header Insertion Spacing
     { "header_spacing", "Header Insertion Spacing",             OFFSET(header_spacing),     AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 1000, VE },
 
+    /// Maximum queued frames
+    { "async_depth",    "Set maximum encoding parallelism. Higher values increase output latency.", OFFSET(hwsurfaces_in_queue_max), AV_OPT_TYPE_INT, {.i64 = 16 }, 1, 16, VE },
+
     /// B-Frames
     // BPicturesPattern=bf
     { "bf_delta_qp",    "B-Picture Delta QP",                   OFFSET(b_frame_delta_qp),   AV_OPT_TYPE_INT,  { .i64 = 4 }, -10, 10, VE },

libavcodec/amfenc_hevc.c

@@ -83,6 +83,8 @@ static const AVOption options[] = {
     { "gop",            "", 0, AV_OPT_TYPE_CONST, { .i64 = AMF_VIDEO_ENCODER_HEVC_HEADER_INSERTION_MODE_GOP_ALIGNED }, 0, 0, VE, .unit = "hdrmode" },
     { "idr",            "", 0, AV_OPT_TYPE_CONST, { .i64 = AMF_VIDEO_ENCODER_HEVC_HEADER_INSERTION_MODE_IDR_ALIGNED }, 0, 0, VE, .unit = "hdrmode" },
 
+    { "async_depth",    "Set maximum encoding parallelism. Higher values increase output latency.", OFFSET(hwsurfaces_in_queue_max), AV_OPT_TYPE_INT, {.i64 = 16 }, 1, 16, VE },
+
     { "high_motion_quality_boost_enable",   "Enable High motion quality boost mode",  OFFSET(hw_high_motion_quality_boost), AV_OPT_TYPE_BOOL,   {.i64 = -1 }, -1, 1, VE },
     { "gops_per_idr",   "GOPs per IDR 0-no IDR will be inserted",   OFFSET(gops_per_idr),  AV_OPT_TYPE_INT,  { .i64 = 1  },  0, INT_MAX, VE },
     { "preencode",      "Enable preencode",                         OFFSET(preencode),     AV_OPT_TYPE_BOOL, { .i64 = -1  },  -1, 1, VE},