[FFmpeg-devel] [PATCH 17/39] avcodec/libxavs: Avoid overallocating, copying packet data

[James Almer]

On 5/21/2021 6:17 AM, Andreas Rheinhardt wrote:
> When the packet size is known in advance like here, one can avoid
> an intermediate buffer for the packet data; also, there is no reason
> to add AV_INPUT_BUFFER_MIN_SIZE to the packet size any more, as the
> actually needed packet size can be easily calculated: It is three bytes
> more than the raw nal size per NALU.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>
> ---
>   libavcodec/libxavs.c | 20 +++++++++++++-------
>   1 file changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/libavcodec/libxavs.c b/libavcodec/libxavs.c
> index 253f4bde6a..ea53c49d38 100644
> --- a/libavcodec/libxavs.c
> +++ b/libavcodec/libxavs.c
> @@ -27,6 +27,7 @@
>   #include <float.h>
>   #include <xavs.h>
>   #include "avcodec.h"
> +#include "encode.h"
>   #include "internal.h"
>   #include "packet_internal.h"
>   #include "libavutil/internal.h"
> @@ -85,18 +86,20 @@ static int encode_nals(AVCodecContext *ctx, AVPacket *pkt,
>                          xavs_nal_t *nals, int nnal)
>   {
>       XavsContext *x4 = ctx->priv_data;
> -    uint8_t *p;
> -    int i, s, ret, size = x4->sei_size + AV_INPUT_BUFFER_MIN_SIZE;
> +    int64_t size = x4->sei_size;
> +    uint8_t *p, *p_end;
> +    int i, s, ret;
>   
>       if (!nnal)
>           return 0;
>   
>       for (i = 0; i < nnal; i++)
> -        size += nals[i].i_payload;
> +        size += 3U + nals[i].i_payload;
>   
> -    if ((ret = ff_alloc_packet2(ctx, pkt, size, 0)) < 0)
> +    if ((ret = ff_get_encode_buffer(ctx, pkt, size, 0)) < 0)
>           return ret;
>       p = pkt->data;
> +    p_end = pkt->data + size;
>   
>       /* Write the SEI as part of the first frame. */
>       if (x4->sei_size > 0 && nnal > 0) {
> @@ -106,12 +109,14 @@ static int encode_nals(AVCodecContext *ctx, AVPacket *pkt,
>       }
>   
>       for (i = 0; i < nnal; i++) {
> +        int size = p_end - p;
>           s = xavs_nal_encode(p, &size, 1, nals + i);
>           if (s < 0)
>               return -1;
> +        if (s != 3U + nals[i].i_payload)
> +            return AVERROR_BUG;

AVERROR_EXTERNAL. This is not a bug in our code or something we can fix 
if it fails, so AVERROR_BUG is not correct (Neither would an assert for 
the same reason).

>           p += s;
>       }
> -    pkt->size = p - pkt->data;
>   
>       return 1;
>   }
> @@ -150,7 +155,7 @@ static int XAVS_frame(AVCodecContext *avctx, AVPacket *pkt,
>   
>       if (!ret) {
>           if (!frame && !(x4->end_of_stream)) {
> -            if ((ret = ff_alloc_packet2(avctx, pkt, 4, 0)) < 0)
> +            if ((ret = ff_get_encode_buffer(avctx, pkt, 4, 0)) < 0)
>                   return ret;
>   
>               pkt->data[0] = 0x0;
> @@ -425,7 +430,8 @@ const AVCodec ff_libxavs_encoder = {
>       .init           = XAVS_init,
>       .encode2        = XAVS_frame,
>       .close          = XAVS_close,
> -    .capabilities   = AV_CODEC_CAP_DELAY | AV_CODEC_CAP_OTHER_THREADS,
> +    .capabilities   = AV_CODEC_CAP_DR1 | AV_CODEC_CAP_DELAY |
> +                      AV_CODEC_CAP_OTHER_THREADS,
>       .caps_internal  = FF_CODEC_CAP_AUTO_THREADS,
>       .pix_fmts       = (const enum AVPixelFormat[]) { AV_PIX_FMT_YUV420P, AV_PIX_FMT_NONE },
>       .priv_class     = &xavs_class,
>