Re: [FFmpeg-devel] [PATCH v2 2/5] avcodec/webp_parser: parse each frame into one packet

[James Zern <jzern-at-google.com@ffmpeg.org>]

On Thu, Jul 6, 2023 at 4:28 AM Thilo Borgmann <thilo.borgmann@mail.de> wrote:
>
> ---
>  libavcodec/webp_parser.c | 132 ++++++++++++++++++++++++++-------------
>  1 file changed, 90 insertions(+), 42 deletions(-)
>
> [...]
> +            } else {
> +                /* read the next tag */
> +                ctx->remaining_file_size--;
> +                if (ctx->remaining_file_size == 0) {
>                      ctx->pc.frame_start_found = 0;
>                      continue;
>                  }
>                  ctx->pc.frame_start_found++;
> -                ctx->remaining_size = ctx->fsize + i - 15;
> -                if (ctx->pc.index + i > 15) {
> -                    next = i - 15;
> -                    state = 0;
> -                    break;
> -                } else {
> -                    ctx->pc.state64 = 0;
> -                    goto restart;
> +                if (ctx->pc.frame_start_found < 8)
> +                    continue;
> +
> +                switch (state >> 32) {
> +                    case MKBETAG('A', 'N', 'M', 'F'):
> +                    case MKBETAG('V', 'P', '8', ' '):
> +                    case MKBETAG('V', 'P', '8', 'L'):

No indent on the case statements.

> +                        if (ctx->frame) {
> +                            ctx->frame = 0;
> +                            next = i - 8;
> +                            state = 0;
> +                            ctx->pc.frame_start_found = 0;
> +                            goto flush;
> +                        }
> +                        ctx->frame = 1;
> +                        break;
> +                    default:
> +                        break;
>                  }
> -            } else if (ctx->pc.frame_start_found)
> -                ctx->pc.frame_start_found++;
> -        }
> -        ctx->pc.state64 = state;
> -    } else {
> -        if (ctx->remaining_size) {
> -            i = FFMIN(ctx->remaining_size, buf_size);
> -            ctx->remaining_size -= i;
> -            if (ctx->remaining_size)
> -                goto flush;
>
> -            ctx->pc.frame_start_found = 0;
> -            goto restart;
> +                ctx->remaining_tag_size = av_bswap32(state);
> +                ctx->remaining_tag_size += ctx->remaining_tag_size & 1;
> +                if (ctx->remaining_tag_size > ctx->remaining_file_size) {
> +                    /* this is probably trash at the end of file */

This would instead mean the file was truncated if remaining_tag_size
fits within the RIFF chunk size. Parsing also looks like it can
continue past the end of the RIFF chunk.
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