[FFmpeg-devel] [PATCH] libsvtav1: Enable 2-pass encoding

[Fredrik Lundkvist]

Currently, libsvtav1 does not send pass number or stat buffer to SVT-AV1, which means that 2-pass encoding is not possible using FFMPEG;
if a user wants to do 2-pass encoding using SVT-AV1, they have to use SvtAv1EncApp.
This patch adds 2-pass encoding support to libsvtav1 using the stats buffers provided by the AVCodecContext.
When encoding the first pass using SVT-AV1, the following should be logged:
Svt[info]: SVT [config]: preset  : Pass 1
Indicating that the encoder knows that it is performing the first pass, activating a special preset.
With the patch applied:
ffmpeg -i input.mp4 -c:v libsvtav1 -an  -pass 1 -b:v 1M -f null /dev/null
[...]
Svt[info]: -------------------------------------------
Svt[info]: SVT [config]: preset  : Pass 1
Svt[info]: -------------------------------------------
[...]

Signed-off-by: Fredrik Lundkvist <fredrik.lundkvist at svt.se<mailto:fredrik.lundkvist at svt.se>>
---
libavcodec/libsvtav1.c | 47 +++++++++++++++++++++++++++++++++++++++++-
1 file changed, 46 insertions(+), 1 deletion(-)

diff --git a/libavcodec/libsvtav1.c b/libavcodec/libsvtav1.c
index 9bc165f0cf..be2189399f 100644
--- a/libavcodec/libsvtav1.c
+++ b/libavcodec/libsvtav1.c
@@ -25,6 +25,7 @@
#include <EbSvtAv1Enc.h>
#include <EbSvtAv1Metadata.h>

+#include "libavutil/base64.h"
#include "libavutil/common.h"
#include "libavutil/frame.h"
#include "libavutil/imgutils.h"
@@ -226,6 +227,34 @@ static int config_enc_params(EbSvtAv1EncConfiguration *param,
        param->max_qp_allowed       = avctx->qmax;
        param->min_qp_allowed       = avctx->qmin;
    }
+
+    if (avctx->flags & AV_CODEC_FLAG_PASS2) {
+        int decode_size, ret;
+        if(!avctx->stats_in) {
+            av_log(avctx, AV_LOG_ERROR, "No stats file for second pass\n");
+            return AVERROR_INVALIDDATA;
+        }
+        param->rc_stats_buffer.sz = strlen(avctx->stats_in) * 3 / 4;
+        ret                       = av_reallocp(&param->rc_stats_buffer.buf, param->rc_stats_buffer.sz);
+        if (ret < 0) {
+            av_log(avctx, AV_LOG_ERROR,
+                    "Stat buffer alloc (%"SIZE_SPECIFIER" bytes) failed \n",
+                    param->rc_stats_buffer.sz
+            );
+            param->rc_stats_buffer.sz = 0;
+            return ret;
+        }
+        decode_size = av_base64_decode(param->rc_stats_buffer.buf, avctx->stats_in, param->rc_stats_buffer.sz);
+        if (decode_size < 0) {
+            av_log(avctx, AV_LOG_ERROR, "Stat buffer decode failed\n");
+            return AVERROR_INVALIDDATA;
+        }
+        param->rc_stats_buffer.sz = decode_size;
+        param->pass = 2;
+    } else if (avctx->flags & AV_CODEC_FLAG_PASS1) {
+        param->pass = 1;
+    }
+
    param->max_bit_rate             = avctx->rc_max_rate;
    if ((avctx->bit_rate > 0 || avctx->rc_max_rate > 0) && avctx->rc_buffer_size)
        param->maximum_buffer_size_ms =
@@ -618,6 +647,23 @@ static int eb_receive_packet(AVCodecContext *avctx, AVPacket *pkt)
    if (headerPtr->flags & EB_BUFFERFLAG_EOS) {
         svt_enc->eos_flag = EOS_RECEIVED;
         svt_av1_enc_release_out_buffer(&headerPtr);
+         if (avctx->flags & AV_CODEC_FLAG_PASS1) {
+            SvtAv1FixedBuf first_pass_stats;
+            EbErrorType ret = svt_av1_enc_get_stream_info(svt_enc->svt_handle, SVT_AV1_STREAM_INFO_FIRST_PASS_STATS_OUT, &first_pass_stats);
+            if (ret == EB_ErrorNone) {
+                size_t b64_size = AV_BASE64_SIZE(first_pass_stats.sz);
+
+                avctx->stats_out = av_malloc(b64_size);
+                if(!avctx->stats_out) {
+                    av_log(avctx, AV_LOG_ERROR, "Stat buffer alloc (%"SIZE_SPECIFIER" bytes) failed\n",
+                            b64_size);
+                    return AVERROR(ENOMEM);
+                }
+                av_base64_encode(avctx->stats_out, b64_size, first_pass_stats.buf, first_pass_stats.sz);
+            } else {
+                av_log(avctx, AV_LOG_ERROR, "Failed to get stream info");
+            }
+         }
         return AVERROR_EOF;
    }
#endif
@@ -681,7 +727,6 @@ static av_cold int eb_enc_close(AVCodecContext *avctx)
        svt_metadata_array_free(&svt_enc->in_buf->metadata);
        av_freep(&svt_enc->in_buf);
    }
-
    av_buffer_pool_uninit(&svt_enc->pool);
    av_frame_free(&svt_enc->frame);
    ff_dovi_ctx_unref(&svt_enc->dovi);
--
2.39.3 (Apple Git-145)