[FFmpeg-devel] [PATCH v3 2/2] avformat: add demuxer for argonaut games' ASF format

[Zane van Iperen]

21/1/20 11:14 pm, Carl Eugen Hoyos пишет:
> 
> Am Di., 21. Jan. 2020 um 11:09 Uhr schrieb Zane van Iperen
> <zane at zanevaniperen.com>:
> 
>> +static int argo_asf_probe(const AVProbeData *p)
>> +{
>> +    int score;
>> +    ArgoASFFileHeader hdr;
>> +
>> +    av_assert0(AVPROBE_PADDING_SIZE >= ASF_FILE_HEADER_SIZE);
>> +
>> +    argo_asf_parse_file_header(&hdr, p->buf);
>> +
>> +    if (hdr.magic != ASF_TAG)
>> +        return 0;
> 
>> +    /* If this is huge, then it's very likely not an ASF file. */
>> +    if (hdr.chunk_offset > INT_MAX)
>> +        return 1;
> 
> Am I correct that this tests only one bit?
> This makes sense for many probe functions that can easily
> return false positives based on weak heuristics, probe
> functions typically return high scores for matching first 32
> bits though.
> 

I can just get rid of that check completely if it's easier.

>> +    score = 0;
>> +    if (argo_asf_is_known_version(&hdr))
>> +        score += (AVPROBE_SCORE_MAX / 2) + 1;
> 
> Unusual code style.
> 
>> +    /* Have only ever seen these with 1 chunk. */
>> +    if (hdr.num_chunks == 1)
>> +        score += 10;
> 
> Returns 0 for argo files with unknown version and more than
> one chunk and 10 for for unknown version and one chunk.
> 
> Should be ~25 in both cases, feel free to return a higher
> score if all tests pass, I just wanted to simplify the probe
> function as testing 32 bit is what is usually done.
> 

Returning 0 on a unknown version is a bug, I want it to hit the
avpriv_request_sample() below.

Would something like this (untested) be better?

 >     if (hdr.chunk_offset & 0xFF000000U)
 >         return 1;
 >
 >     score = (AVPROBE_SCORE_MAX / 2) + 1;
 >
 >     if (!argo_asf_is_known_version(&hdr))
 >         score -= 25;
 >
 >     /* Have only ever seen these with 1 chunk. */
 >     if (hdr.num_chunks > 1)
 >         score -= 25;
 >
 >     return score;

That way if it fails one check it'll be 26, or 1 if it fails both.

> Carl Eugen
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Zane