Re: [FFmpeg-devel] [PATCH v2 5/5] libavformat/webp: add WebP demuxer

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

On Thu, Jul 6, 2023 at 4:28 AM Thilo Borgmann <thilo.borgmann@mail.de> wrote:
>
> From: Josef Zlomek <josef@pex.com>
>
> Adds the demuxer of animated WebP files.
> It supports non-animated, animated, truncated, and concatenated files.
> Reading from a pipe (and other non-seekable inputs) is also supported.
>
> The WebP demuxer splits the input stream into packets containing one frame.
> It also marks the key frames properly.
> The loop count is ignored by default (same behaviour as animated PNG and GIF),
> it may be enabled by the option '-ignore_loop 0'.
>
> The frame rate is set according to the frame delay in the ANMF chunk.
> If the delay is too low, or the image is not animated, the default frame rate
> is set to 10 fps, similarly to other WebP libraries and browsers.
> The fate suite was updated accordingly.
>
> Signed-off-by: Josef Zlomek <josef@pex.com>
> ---
>  Changelog                                   |   1 +
>  doc/demuxers.texi                           |  28 +
>  libavformat/Makefile                        |   1 +
>  libavformat/allformats.c                    |   1 +
>  libavformat/version.h                       |   2 +-
>  libavformat/webpdec.c                       | 733 ++++++++++++++++++++
>  tests/ref/fate/webp-rgb-lena-lossless       |   2 +-
>  tests/ref/fate/webp-rgb-lena-lossless-rgb24 |   2 +-
>  tests/ref/fate/webp-rgb-lossless            |   2 +-
>  tests/ref/fate/webp-rgb-lossy-q80           |   2 +-
>  tests/ref/fate/webp-rgba-lossless           |   2 +-
>  tests/ref/fate/webp-rgba-lossy-q80          |   2 +-
>  12 files changed, 771 insertions(+), 7 deletions(-)
>  create mode 100644 libavformat/webpdec.c
>
> [...]
> +        switch (chunk_type) {
> +        case MKTAG('R', 'I', 'F', 'F'):
> +            if (avio_tell(pb) != wdc->file_start + 8) {
> +                // premature RIFF found, shorten the file size
> +                WebPHeaders *tmp = webp_headers_lower_or_equal(wdc->webp_headers,
> +                                                               wdc->num_webp_headers,
> +                                                               avio_tell(pb));
> +                tmp->webp_size -= wdc->remaining_size;
> +                wdc->remaining_size = 0;
[...]
> +
> +    if (wdc->remaining_size > 0 && avio_feof(pb)) {
> +        // premature EOF, shorten the file size

I'm not sure about this. If the file is truncated shouldn't this be
treated as an error?
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