Hi Peter

full review below as our native decoder still is not finished

[...]
> diff --git a/libavcodec/allcodecs.c b/libavcodec/allcodecs.c
> index f10519617e..5f8f682111 100644
> --- a/libavcodec/allcodecs.c
> +++ b/libavcodec/allcodecs.c

> @@ -810,8 +810,9 @@ extern FFCodec ff_libvpx_vp9_encoder;
>  extern const FFCodec ff_libvpx_vp9_decoder;
>  extern const FFCodec ff_libvvenc_encoder;
>  /* preferred over libwebp */
> -extern const FFCodec ff_libwebp_anim_encoder;
>  extern const FFCodec ff_libwebp_encoder;
> +extern const FFCodec ff_libwebp_anim_encoder;

please dont reorder things in this patch, its unrelated



> +extern const FFCodec ff_libwebp_decoder;
>  extern const FFCodec ff_libx262_encoder;
>  extern const FFCodec ff_libx264_encoder;
>  extern const FFCodec ff_libx264rgb_encoder;
> diff --git a/libavcodec/libwebpdec.c b/libavcodec/libwebpdec.c
> new file mode 100644
> index 0000000000..e9ca65ef05
> --- /dev/null
> +++ b/libavcodec/libwebpdec.c
> @@ -0,0 +1,192 @@
> +/*
> + * LibWebP decoder
> + * Copyright (c) 2025 Peter Xia
> + *
> + * This file is part of FFmpeg.
> + *
> + * FFmpeg is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * FFmpeg is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with FFmpeg; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +/**
> + * @file
> + * LibWebP decoder
> + */
> +
> +#include "decode.h"
> +#include "codec_internal.h"
> +#include "libavutil/avutil.h"
> +#include "libavutil/opt.h"
> +#include "libavformat/avformat.h"
> +#include "libavformat/avio.h"
> +
> +#include <webp/demux.h>
> +#include <webp/decode.h>
> +
> +typedef struct AnimatedWebPContext
> +{
> +    const AVClass *class;
> +    WebPAnimDecoderOptions dec_options;
> +    WebPAnimDecoder *dec;
> +    AVBufferRef *file_content;
> +    WebPData webp_data; // references |file_content|
> +    uint32_t loop_to_send;
> +    uint32_t loop_sent;
> +
> +    // --- Options ---
> +    int ignore_loop;
> +} AnimatedWebPContext;
> +
> +// Initialize the decoder context
> +static av_cold int decode_libwebp_init(AVCodecContext *avctx)
> +{
> +    AnimatedWebPContext *s = avctx->priv_data;
> +
> +    if (!WebPAnimDecoderOptionsInit(&s->dec_options)) {
> +        av_log(avctx, AV_LOG_DEBUG, "Cannot initialize WebPAnimDecoderOptions\n");
> +        return AVERROR(ENOMEM);
> +    }
> +    s->dec_options.color_mode = MODE_RGBA;
> +    s->dec_options.use_threads = 1;
> +    s->file_content = NULL;
> +    s->loop_sent = 0;
> +
> +    avctx->pix_fmt = AV_PIX_FMT_RGBA;

> +    avctx->pkt_timebase = av_make_q(1, 1000);

violates API "* - decoding: set by user." the decoder is not the user


> +    avctx->framerate = av_make_q(1, 0);
> +
> +    av_log(avctx, AV_LOG_DEBUG, "Animated WebP decoder initialized.\n");
> +    return 0; // Success
> +}
> +
> +/**
> + * Decode one frame of the animated WebP.
> + * This function will be called multiple times by FFmpeg.
> + * The first call receives the AVPacket with the full WebP file.
> + * Subsequent calls receive empty AVPacket until all frames are decoded.
> + */
> +static int decode_libwebp_frame(AVCodecContext *avctx, AVFrame *p,
> +                                int *got_frame, AVPacket *avpkt)
> +{
> +    WebPAnimInfo anim_info;
> +    uint8_t *frame_rgba;
> +    int timestamp_ms;
> +
> +    AnimatedWebPContext *s = avctx->priv_data;
> +    int ret = avpkt->size;
> +
> +    // Initialization Phase (First Call)
> +    // |avpkt| contains the entire file.
> +    if (!s->dec) {
> +        if (!avpkt || avpkt->size <= 0) {
> +            // Should not happen on the first call, but check anyway.
> +            av_log(avctx, AV_LOG_ERROR, "No input data provided on first call.\n");
> +            return AVERROR(EINVAL);
> +        }
> +
> +        // Store entire WebP file in memory.

> +        s->file_content = av_buffer_ref(avpkt->buf);
> +        s->webp_data.bytes = s->file_content->data;

Missing failure check for av_buffer_ref()



> +        s->webp_data.size = s->file_content->size;
> +
> +        s->dec = WebPAnimDecoderNew(&s->webp_data, &s->dec_options);
> +        if (!s->dec) {
> +            av_log(avctx, AV_LOG_ERROR, "Error creating WebPAnimDecoder.\n");
> +            av_buffer_unref(&s->file_content);
> +            return AVERROR(ENOMEM);
> +        }
> +

> +        WebPAnimDecoderGetInfo(s->dec, &anim_info);
> +
> +        s->loop_to_send = s->ignore_loop ? 1 : anim_info.loop_count;

> +        avctx->width = anim_info.canvas_width;
> +        avctx->coded_width = anim_info.canvas_width;
> +        avctx->height = anim_info.canvas_height;
> +        avctx->coded_height = anim_info.canvas_height;

probably this should use ff_set_dimensions()


> +        avctx->framerate = av_make_q(1, 0);

Why ?


> +    }
> +
> +    if (!WebPAnimDecoderHasMoreFrames(s->dec)) {
> +        s->loop_sent++;
> +        WebPAnimDecoderReset(s->dec);
> +    }
> +
> +    if (s->loop_sent >= s->loop_to_send) {
> +        av_log(avctx, AV_LOG_DEBUG, "End of animated WebP stream.\n");
> +        return AVERROR_EOF;
> +    }
> +
> +
> +    if (!WebPAnimDecoderGetNext(s->dec, &frame_rgba, &timestamp_ms)) {
> +        av_log(avctx, AV_LOG_ERROR, "Error getting next frame from WebPAnimDecoder.\n");
> +        return AVERROR(EINVAL);
> +    }
> +
> +    ret = ff_get_buffer(avctx, p, 0);

> +    if (ret) {

ret < 0


> +        av_log(avctx, AV_LOG_ERROR, "Failed to allocated buffer.\n");
> +        return AVERROR(ENOMEM);
> +    }
> +

> +    p->width = avctx->width;
> +    p->height = avctx->height;
> +    p->format = AV_PIX_FMT_RGBA;

why is this needed ?


> +    p->pts = timestamp_ms;

> +    p->pkt_dts = 0;

why ?


> +    p->pict_type = AV_PICTURE_TYPE_I;
> +

> +    memcpy(p->data[0], frame_rgba, p->width * p->height * 4);

ignores linesize also cant the lib render directly into the frame


[...]

> diff --git a/libavcodec/version.h b/libavcodec/version.h
> index 0d4156e74a..026609f410 100644
> --- a/libavcodec/version.h
> +++ b/libavcodec/version.h
> @@ -30,7 +30,7 @@
>  #include "version_major.h"
>  
>  #define LIBAVCODEC_VERSION_MINOR   0
> -#define LIBAVCODEC_VERSION_MICRO 101
> +#define LIBAVCODEC_VERSION_MICRO 102

minor should be bumped

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Observe your enemies, for they first find out your faults. -- Antisthenes