[FFmpeg-devel] [PATCH] avformat/img2dec: return immediately in jpeg_probe() when EOI is found

[Carl Eugen Hoyos]

Am Mi., 1. Apr. 2020 um 18:01 Uhr schrieb Matthieu Bouron
<matthieu.bouron at gmail.com>:
>
> Fixes probing of JPEG files containing MPF metadata appended at the end
> of the file.
>
> The MPF metadata chunk can contains multiple JPEG images (thumbnails)
> which makes the jpeg_probe fails (return 0) because it finds a SOI
> marker after EOI.
> ---
>
> This patch fixes probing of JPEG files containing MPF metadata [1] appended
> at the end of the file.
>
> Such files can be produced by GoPro camera (which produces JPEG files
> with MPF metadata).
>
> You can find a sample here:
> https://0x5c.me/gopro_jpg_mpf_probe_fail
>
> To reproduce the issue using ffmpeg master:
> wget https://0x5c.me/gopro_jpg_mpf_probe_fail
> ./ffmpeg -formatprobesize 5000000 -i gopro_jpg_mpf_probe_fail
>
> I removed intentionally the jpeg extension from the filename so the
> image2 demuxer is not used.
>
> Current ffmpeg master won't still be able to decode this file because of a
> "regression" introduced by ec3d8a0e6945fe015d16cd98a1e7dbb4be815c15 on
> the mjpeg_parser.
> The jpeg_pipe demuxer outputs partial chunks of the jpeg file that the
> mjpeg decoder can't handle (it needs the whole data). Before
> ec3d8a0e6945fe015d16cd98a1e7dbb4be815c15, the mjpeg_parser was
> outputting a complete frame.
>
> If the parser is correct as is, another way to fix this issue whould be
> to add AVSTREAM_PARSE_HEADERS to the need_parsing flags from the
> jpeg_pipe demuxer, ie:
>
> --- a/libavformat/img2dec.c
> +++ b/libavformat/img2dec.c
> @@ -209,7 +209,7 @@ int ff_img_read_header(AVFormatContext *s1)
>          s->is_pipe = 0;
>      else {
>          s->is_pipe       = 1;
> -        st->need_parsing = AVSTREAM_PARSE_FULL;
> +        st->need_parsing = AVSTREAM_PARSE_FULL | AVSTREAM_PARSE_HEADERS;
>
> Settings AVSTREAM_PARSE_HEADERS makes avformat requests complete frames
> from the parser in libavformat/utils.c
>
> What do you think ?

Why is your sample not detected by the mjpeg demuxer?

I suspect your patch breaks the mjpeg demuxer.

> [1] https://exiftool.org/TagNames/MPF.html
>
> ---
>  libavformat/img2dec.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
>
> diff --git a/libavformat/img2dec.c b/libavformat/img2dec.c
> index 93cd51c1932..decd8023e02 100644
> --- a/libavformat/img2dec.c
> +++ b/libavformat/img2dec.c
> @@ -773,9 +773,7 @@ static int jpeg_probe(const AVProbeData *p)
>          case EOI:
>              if (state != SOS)
>                  return 0;
> -            state = EOI;
> -            break;
> -        case DHT:
> +            return AVPROBE_SCORE_EXTENSION + 1;

I don't think this is correct.

>          case DQT:
>          case APP0:
>          case APP1:
> @@ -803,8 +801,6 @@ static int jpeg_probe(const AVProbeData *p)
>          }
>      }
>

> -    if (state == EOI)
> -        return AVPROBE_SCORE_EXTENSION + 1;

>      if (state == SOS)
>          return AVPROBE_SCORE_EXTENSION / 2;
>      return AVPROBE_SCORE_EXTENSION / 8;

Carl Eugen