[FFmpeg-devel] [PATCH] lavf/mp3dec: fix mp3 file probe fail

[James Almer]

On 12/12/2017 4:38 AM, wm4 wrote:
> On Mon, 11 Dec 2017 22:56:24 +0100
> Michael Niedermayer <michael at niedermayer.cc> wrote:
> 
>> On Mon, Dec 11, 2017 at 11:43:30AM +0100, wm4 wrote:
>>> On Fri, 8 Dec 2017 18:51:52 +0100
>>> Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:
>>>   
>>>> 2017-12-08 18:45 GMT+01:00 Tiejun.Peng <tiejun.peng at foxmail.com>:  
>>>>> i agree with you. too much  experience value in condition of Judgement  like this:
>>>>> "else if(max_frames>=4 && max_frames >= p->buf_size/10000)".
>>>>>  why  it is the value ? it is hard to known.
>>>>> maybe  the work of cleaned up  need a few days, so i just  repair of the probe.    
>>>>
>>>> Please be careful:
>>>> As you already know, this probe function is the result of many
>>>> user reports, many tests and turning many knobs. You cannot
>>>> "repair" it (easily).
>>>>
>>>> If you know of any false positives of the current probe function,
>>>> please report them!  
>>>
>>> It plays ELF files as mp3.
>>>
>>> You've been ignoring this issue, though.
>>>
>>> This probe function is really pretty bad.  
>>
>> The probe code determines the most likely format from the set of
>> supported formats.
>> We do not support playing excutable files (that makes no sense), thus
>> these do not get detected.
>>
>> Is there a usecase where detecting not just the most likely multimedia
>> format but detecting that a file is not any multimedia format
>> makes sense ?
> 
> Not playing noise and looking like a huge fuckup of a media application
> when opening a bunch of files that might include unknown file types?
> Lots of software is using this to detect whether something is a media
> file in the first place, too.
> 
>> Also if a format is detected with a low score the user is informed about
>> this via "Format %s detected only with low score of %d,"
> 
> Doesn't help much if legitimate files get a low probe score. AFAIK in
> my case this happened mostly because of large ID3v2 tags, which
> restricted or even removed any useful media data from the probe buffer.
> An API to detect id3 tags (and their size to skip them) would probably
> be nice for this.

ID3v2 tags are handled in avformat_open_input(), unlike APE tags. If
it's not currently being skipped before filling the probe buffers, it
could perhaps be implemented.