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

[James Almer <jamrial@gmail.com>]

On 5/15/2024 11:14 AM, Fredrik Lundkvist via ffmpeg-devel wrote:
> 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@svt.se<mailto:fredrik.lundkvist@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) {

if (...

> +            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;

nit: AV_BASE64_DECODE_SIZE

> +        ret                       = av_reallocp(&param->rc_stats_buffer.buf, param->rc_stats_buffer.sz);

Why realloc instead of malloc?

> +        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) {

Wouldn't it be safer to free rc_stats_buffer.buf and set 
rc_stats_buffer.sz to 0 on failure here too?


> +            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) {

No brackets for single line blocks.

> +        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);

svt_ret. Don't shadow ret.

Also, consider splitting this line.

> +            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) {

Missing space after the if again.

> +                    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);

Unchecked return value.

> +            } else {

Single line block again.

> +                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);
>      }
> -

Spurious change.

>      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)
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