[FFmpeg-devel] confusing trailing metadata for mpeg frames

[Michael Niedermayer]

On Mon, Sep 27, 2010 at 12:20:27PM -0700, David Byron wrote:

i take the liberty to skip most of your talk and patch
(they look by a factor >10 too big for what they do)

[...]

> @@ -174,8 +274,28 @@ static int mp3_read_header(AVFormatContext *s,
>  static int mp3_read_packet(AVFormatContext *s, AVPacket *pkt)
>  {
>      int ret, size;
> +    MP3Context *mp3 = s->priv_data;
> +    int64_t pos;
> +
>      //    AVStream *st = s->streams[0];
>  
> +    /* If we're into the trailing metadata, don't look for a packet */
> +    if (mp3->trailing_metadata_offset != -1) {
> +        pos = url_ftell(s->pb);
> +        av_log(s, AV_LOG_DEBUG, "%s: \"%s\": current offset: %" PRId64 ", "
> +               "trailing_metadata_offset: %" PRId64 "\n", __FUNCTION__,
> +               s->filename, pos, mp3->trailing_metadata_offset);
> +
> +        if (pos < 0)
> +            return pos;
> +        if (pos >= mp3->trailing_metadata_offset) {
> +            av_log(s, AV_LOG_DEBUG, "%s: \"%s\": giving up at offset: %"
> +                   PRId64 " due to trailing metadata\n", __FUNCTION__,
> +                   s->filename, pos);
> +            return AVERROR_EOF;
> +        }
> +    }
> +
>      size= MP3_PACKET_SIZE;

how could this in any form work?

you want to truncate the data but you do NOT truncate you leave size as a
constant and only check once you already have read too far
if you want to win the most buggy patch of the month award you have a good
chance for that

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

If a bugfix only changes things apparently unrelated to the bug with no
further explanation, that is a good sign that the bugfix is wrong.
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