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

[Thilo Borgmann]

Am 12.07.23 um 03:22 schrieb James Zern:
> On Thu, Jul 6, 2023 at 4:28 AM Thilo Borgmann <thilo.borgmann at mail.de> wrote:
>>
>> From: Josef Zlomek <josef at 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 at 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?

Either it might be worth trying to decode what is left,
or the size in the header might have even been damaged.

Thanks,
Thilo