Re: [FFmpeg-devel] [PATCH] avformat: add CRI USM demuxer

[Paul B Mahol <onemda@gmail.com>]

On Wed, Sep 6, 2023 at 1:30 PM Andreas Rheinhardt <
andreas.rheinhardt@outlook.com> wrote:

> Paul B Mahol:
> > On Wed, Sep 6, 2023 at 11:26 AM Andreas Rheinhardt <
> > andreas.rheinhardt@outlook.com> wrote:
> >
> >> Paul B Mahol:
> >>>
> >>> +    chunk_type = avio_rb32(pb);
> >>> +    chunk_size = avio_rb32(pb);
> >>
> >> You are not checking whether the chunk here exceeds its containing
> chunk.
> >>
> >>>
> >>> +    av_fast_malloc(&usm->header, &usm->header_size,
> >>> +                   chunk_size + AV_INPUT_BUFFER_PADDING_SIZE);
> >>> +    if (!usm->header)
> >>> +        return AVERROR(ENOMEM);
> >>
> >> The bytestream2 API does not rely on the buffer being padded at all.
> >>
> >>>
> >>> +    bytestream2_skip(&sgb, string_offset);
> >>
> >> This is unnecessary, because you seek with an absolute offset lateron
> >> anyway before using sgb.
> >>
> >>>
> >>> +        bytestream2_seek(&sgb, string_offset + offset, SEEK_SET);
> >>> +        while (bytestream2_get_bytes_left(&sgb) > 0) {
> >>> +            key[n] = bytestream2_get_byte(&sgb);
> >>> +            if (!key[n])
> >>> +                break;
> >>> +            if (n >= sizeof(key) - 1)
> >>> +                break;
> >>> +            n++;
> >>> +        }
> >>> +        key[n] = '\0';
> >>
> >> IMO this would be easier with strnlen(), avoiding sgb altogether.
> >> You would of course need to explicitly check that you are not
> >> overreading, but that is good practice anyway.
> >>
> >>>
> >>> +    chunk_start = avio_tell(pb);
> >>> +    avio_skip(pb, 1);
> >>> +    payload_offset = avio_r8(pb);
> >>> +    padding_size = avio_rb16(pb);
> >>> +    stream_index = avio_r8(pb);
> >>> +    avio_skip(pb, 2);
> >>> +    payload_type = avio_r8(pb);
> >>> +    frame_time = avio_rb32(pb);
> >>> +    frame_rate = avio_rb32(pb);
> >>> +    avio_skip(pb, 8);
> >>
> >> payload_offset and frame_time are set-but-unused; this might lead to
> >> compiler warnings.
> >>
> >>> +        if (usm->ch[is_audio][stream_index].used == 1) {
> >>> +            uint32_t pkt_size = chunk_size - (avio_tell(pb) -
> >> chunk_start);
> >>> +
> >>
> >> This is unnecessary: Unless we already had a read error, pkt_size is
> >> chunk_size - (1 + 1 + 2 + 1 + 2 + 1 + 4 + 4 + 8).
> >>
> >> (Notice that in case padding_size is > 0, it will be part of the packet
> >> with the current code; not sure if that is an issue.)
> >>
> >>>
> >>> +
> >>> +    avio_skip(pb, padding_size);
> >>> +    avio_skip(pb, chunk_size - (avio_tell(pb) - chunk_start));
> >>> +
> >>
> >> Simpler to just use avio_seek(pb, chunk_start + chunk_size, SEEK_SET);
> >>
> >
> > But input might not be seekable.
> >
>
> And? You know that avio_skip(pb, offset) is just avio_seek(pb, offset,
> SEEK_CUR)?
>

And? Do you know that SEEK_SET is different from SEEK_CUR with positive
argument.


>
> - Andreas
>
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