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

[Gyan Doshi <ffmpeg@gyani.pro>]

On 2025-04-13 10:12 pm, Zhao Zhili wrote:
>
>> On Apr 13, 2025, at 19:15, Gyan Doshi <ffmpeg@gyani.pro> wrote:
>>
>> Utility function to report seekability features for a given input.
>>
>> Useful for ffprobe and to extend seek possibilities in fftools.
>> ---
>> 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..e00f1ed0d9 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_NORMAL     0x01 ///< I/O is seekable like a local file
>> +#define AVSEEKABLE_PROTOCOL   0x02 ///< I/O seek is through protocol request via avio_seek_time
>> +#define AVSEEKABLE_DEMUXER    0x04 ///< demuxer has a seek function
>> +#define AVSEEKABLE_PKTSCAN    0x08 ///< seek is performed by consuming and scanning packet timestamps
>> +#define AVSEEKABLE_TIME       0x10 ///< seek target can be a timestamp
>> +#define AVSEEKABLE_BYTE       0x20 ///< seek target can be in bytes
>> +#define AVSEEKABLE_FRAME      0x40 ///< seek target can be a frame index
>> +#define AVSEEKABLE_PTS       0x100 ///< seek target timestamp is expected to be PTS
>> +#define AVSEEKABLE_FAST      0x200 ///< demuxer allows fast but inaccurate seeking
>> +#define AVSEEKABLE_FWDONLY   0x400 ///< set seek will be equal or forward of specified seek point
>> +
>> +/**
>> + * Report if and how a seek can be performed in a given input.
>> + *
>> + * @param s            media file handle
>> + *
>> + * @return 0 if no seek can be performed on input,
>> + *         -1 if the fmt ctx is NULL or is not an input
>> + *         else return AVSEEKABLE_ bitflags indicating seekability features.
>> + */
>> +int avformat_query_seekable(AVFormatContext *s);
>> +
>> /**
>>   * Discard all internally buffered data. This can be useful when dealing with
>>   * discontinuities in the byte stream. Generally works only with formats that
>> diff --git a/libavformat/seek.c b/libavformat/seek.c
>> index c0d94371e6..776a09744a 100644
>> --- a/libavformat/seek.c
>> +++ b/libavformat/seek.c
>> @@ -712,6 +712,59 @@ int avformat_seek_file(AVFormatContext *s, int stream_index, int64_t min_ts,
>>      return ret;
>> }
>>
>> +int avformat_query_seekable(AVFormatContext *s)
>> +{
>> +    int ret = 0;
>> +
>> +    if (!s || !s->iformat)
>> +        return -1;
>> +
>> +    if (!(s->pb && s->pb->seekable) || s->ctx_flags & AVFMTCTX_UNSEEKABLE)
>> +        return 0;
> I think RTSP doesn’t follow this rule, it’s seekable.

Ah, yes, the protocol implemented as a demuxer. Will add an exception.

Regards,
Gyan


>
>> +
>> +    if (s->pb->seekable & AVIO_SEEKABLE_NORMAL)
>> +        ret |= AVSEEKABLE_NORMAL;
>> +
>> +    if (s->pb->seekable & AVIO_SEEKABLE_TIME)
>> +        ret |= AVSEEKABLE_PROTOCOL;
>> +
>> +    if (ffifmt(s->iformat)->read_seek || ffifmt(s->iformat)->read_seek2)
>> +        ret |= AVSEEKABLE_DEMUXER;
>> +
>> +    if (ffifmt(s->iformat)->read_timestamp && !(s->iformat->flags & AVFMT_NOBINSEARCH))
>> +        ret |= AVSEEKABLE_PKTSCAN;
>> +
>> +    if (!(s->iformat->flags & AVFMT_NOTIMESTAMPS))
>> +        ret |= AVSEEKABLE_TIME;
>> +
>> +    // TODO: incomplete, a few demuxers don't set flag but error out on byte seek
>> +    if (!(s->iformat->flags & AVFMT_NO_BYTE_SEEK))
>> +        ret |= AVSEEKABLE_BYTE;
>> +
>> +    // TODO: no flag for frame seeking. Add flag and update this check
>> +    if (s->iformat->flags & 0)
>> +        ret |= AVSEEKABLE_FRAME;
>> +
>> +    if (s->iformat->flags & AVFMT_SEEK_TO_PTS)
>> +        ret |= AVSEEKABLE_PTS;
>> +
>> +    // TODO: flag exists but not added to the demuxers which support it
>> +    if (s->iformat->flags & AVFMT_FLAG_FAST_SEEK)
>> +        ret |= AVSEEKABLE_FAST;
>> +
>> +    if (!(ret & AVSEEKABLE_DEMUXER) && ret & AVSEEKABLE_PKTSCAN)
>> +        ret |= AVSEEKABLE_FWDONLY;
>> +
>> +    if ( !(ret & AVSEEKABLE_DEMUXER) &&
>> +         !(ret & AVSEEKABLE_PKTSCAN) &&
>> +         !(ret & AVSEEKABLE_BYTE) &&
>> +         !(ret & AVSEEKABLE_PROTOCOL) &&
>> +         (s->iformat->flags & AVFMT_NOGENSEARCH) )
>> +        ret = 0;
>> +
>> +    return ret;
>> +}
>> +
>> /** Flush the frame reader. */
>> void ff_read_frame_flush(AVFormatContext *s)
>> {
>> diff --git a/libavformat/version.h b/libavformat/version.h
>> index 752aac16f7..a7c80dc564 100644
>> --- a/libavformat/version.h
>> +++ b/libavformat/version.h
>> @@ -31,7 +31,7 @@
>>
>> #include "version_major.h"
>>
>> -#define LIBAVFORMAT_VERSION_MINOR   0
>> +#define LIBAVFORMAT_VERSION_MINOR   1
>> #define LIBAVFORMAT_VERSION_MICRO 100
>>
>> #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
>> -- 
>> 2.49.0
>>
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