Re: [FFmpeg-devel] [PATCH v2 1/2] avformat: add avformat_query_seekable

[Gyan Doshi <ffmpeg@gyani.pro>]

On 2025-04-21 11:59 pm, Stefano Sabatini wrote:
> On date Tuesday 2025-04-15 16:09:56 +0530, Gyan Doshi wrote:
>> Utility function to report seekability features for a given input.
>>
>> Useful for ffprobe and to extend seek possibilities in fftools.
>> ---
>> v2:
>>     made constants more descriptive
>>     add exception for rtsp false negative seekability
>>
>>   doc/APIchanges         |  3 +++
>>   libavformat/avformat.h | 22 ++++++++++++++++++
>>   libavformat/seek.c     | 53 ++++++++++++++++++++++++++++++++++++++++++
>>   libavformat/version.h  |  2 +-
>>   4 files changed, 79 insertions(+), 1 deletion(-)
>>
>> diff --git a/doc/APIchanges b/doc/APIchanges
>> index 65bf5a9419..879f56b572 100644
>> --- a/doc/APIchanges
>> +++ b/doc/APIchanges
>> @@ -2,6 +2,9 @@ The last version increases of all libraries were on 2025-03-28
>>   
>>   API changes, most recent first:
>>   
>> +2025-04-xx - xxxxxxxxxx - lavf 62.1.100 - avformat.h
>> +  Add avformat_query_seekable().
>> +
>>   2025-04-07 - 19e9a203b7 - lavu 60.01.100 - dict.h
>>     Add AV_DICT_DEDUP.
>>   
>> diff --git a/libavformat/avformat.h b/libavformat/avformat.h
>> index 498c3020a5..f9da5e9e79 100644
>> --- a/libavformat/avformat.h
>> +++ b/libavformat/avformat.h
>> @@ -2338,6 +2338,28 @@ int av_seek_frame(AVFormatContext *s, int stream_index, int64_t timestamp,
>>    */
>>   int avformat_seek_file(AVFormatContext *s, int stream_index, int64_t min_ts, int64_t ts, int64_t max_ts, int flags);
>>   
>> +#define AVSEEKABLE_IO_NORMAL       0x00000001 ///< I/O is seekable like a local file
>> +#define AVSEEKABLE_IO_PROTOCOL     0x00000002 ///< I/O seek is through protocol request via avio_seek_time
>> +#define AVSEEKABLE_VIA_DEMUXER     0x00000004 ///< demuxer has a seek function
>> +#define AVSEEKABLE_VIA_PKTSCAN     0x00000008 ///< seek is performed by consuming and scanning packet timestamps
>> +#define AVSEEKABLE_BY_TIME         0x00000100 ///< seek target can be a timestamp
>> +#define AVSEEKABLE_BY_BYTE         0x00000200 ///< seek target can be in bytes
>> +#define AVSEEKABLE_BY_FRAME        0x00000400 ///< seek target can be a frame index
>> +#define AVSEEKABLE_PROP_PTS        0x00010000 ///< seek target timestamp is expected to be PTS
>> +#define AVSEEKABLE_PROP_FAST       0x00020000 ///< demuxer allows fast but inaccurate seeking
>> +#define AVSEEKABLE_PROP_FWDONLY    0x00040000 ///< set seek will be equal or forward of specified seek point
> Not sure I get this, can you clarify/expand?

The framework does not seek to an earlier KF, e.g. if either avio is not 
AVIO_SEEKABLE_NORMAL or the index does not correctly mark keyframes. 
then a seek to 12s will return frames from 12s and decoding will start 
from next KF encountered.
I see now that my test for this can produce false postives. I'll try to 
fix it.

>> +/**
>> + * Report if and how a seek can be performed in a given input.
> I don't like the "can be performed in a given input" part, I'd use a
> terminology closer to the function name: "for this format context".
>
> Also, probably we want to specify that the method should be used after
> the open operation or whatever.

Will do.

Regards,
Gyan
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