[FFmpeg-devel] [PATCH v3] lavc/libvpx: remove thread limit

[Dmitrii Ovchinnikov]

From: Dmitrii Ovchinnikov <ovchinnikov.dmitrii at gmail.com>

This change improves the performance and multicore
 scalability of the vp9 codec for streaming single-pass encoded videos. The
 current thread limit for ffmpeg codecs is 16 (MAX_AUTO_THREADS in
 pthread_internal.h) due to a limitation in H.264 codec that prevents more
 than 16 threads being used.

Increasing the thread limit to 64 for vp9 improves
the performance for encoding 4K raw videos for streaming by up to 47%
compared to 16 threads, and from 20-30% for 32 threads, with the same quality
as measured by the VMAF score.

Did not need to add a check for limit in libvpx as it is already present 
in libvpx/vp9/vp9_cx_iface.c:
  RANGE_CHECK_HI(cfg, g_threads, 64);
As demonstrated by following message when -threads is set to anything more than 64
[libvpx-vp9 @ 0x30ed380]   Additional information: g_threads out of range [..64]

---
 libavcodec/libvpxdec.c | 2 +-
 libavcodec/libvpxenc.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/libavcodec/libvpxdec.c b/libavcodec/libvpxdec.c
index 9cd2c56caf..19407092d0 100644
--- a/libavcodec/libvpxdec.c
+++ b/libavcodec/libvpxdec.c
@@ -88,7 +88,7 @@ static av_cold int vpx_init(AVCodecContext *avctx,
                             const struct vpx_codec_iface *iface)
 {
     struct vpx_codec_dec_cfg deccfg = {
-        .threads = FFMIN(avctx->thread_count ? avctx->thread_count : av_cpu_count(), 16)
+        .threads = avctx->thread_count ? avctx->thread_count : av_cpu_count()
     };
 
     av_log(avctx, AV_LOG_INFO, "%s\n", vpx_codec_version_str());
diff --git a/libavcodec/libvpxenc.c b/libavcodec/libvpxenc.c
index 9aa5510c28..0627e13973 100644
--- a/libavcodec/libvpxenc.c
+++ b/libavcodec/libvpxenc.c
@@ -942,7 +942,7 @@ static av_cold int vpx_init(AVCodecContext *avctx,
     enccfg.g_timebase.num = avctx->time_base.num;
     enccfg.g_timebase.den = avctx->time_base.den;
     enccfg.g_threads      =
-        FFMIN(avctx->thread_count ? avctx->thread_count : av_cpu_count(), 16);
+        avctx->thread_count ? avctx->thread_count : av_cpu_count();
     enccfg.g_lag_in_frames= ctx->lag_in_frames;
 
     if (avctx->flags & AV_CODEC_FLAG_PASS1)
-- 
2.38.1.windows.1