[FFmpeg-devel] [PATCH] RTMP seek support

[Michael Niedermayer]

On Thu, Apr 01, 2010 at 01:11:24PM -0700, Howard Chu wrote:
> Michael Niedermayer wrote:
>> On Wed, Mar 31, 2010 at 05:24:49PM -0700, Howard Chu wrote:
>>> Howard Chu wrote:
>>>> Michael Niedermayer wrote:
>>>>> removial is planed but the new API might be changed if we find the need
>>>>> to change it still ...
>>>
>>> It seems to me that one thing that ought to be changed is that rescaling
>>> the timestamp should still be done by the caller, not in read_seek2. 
>>> Right
>>> now each implementation of read_seek2() has to duplicate this code.
>>
>> if rescaling is done outside then exact seeking becomes impossible
>> because rescaling implicates rounding
>
> But that's always true, regardless. If you sepcify a seek timestamp in 
> nanoseconds and the stream only supports microseconds, it is going to have 
> to round anyway.

there are normally several streams, and their timebases normally differ.


>
>>> Index: libavformat/flvdec.c
>>> ===================================================================
>>> --- libavformat/flvdec.c	(revision 22713)
>>> +++ libavformat/flvdec.c	(working copy)
>>> @@ -442,6 +442,38 @@
>>>       return ret;
>>>   }
>>>
>>> +static int flv_read_seek(AVFormatContext *s, int stream_index,
>>> +    int64_t ts, int flags)
>>> +{
>>> +    return av_url_read_fseek(s->pb, stream_index, ts, flags);
>>> +}
>>> +
>>> +static int flv_read_seek2(AVFormatContext *s, int stream_index,
>>> +    int64_t min_ts, int64_t ts, int64_t max_ts, int flags)
>>> +{
>>> +    int ret = AVERROR_NOTSUPP;
>>> +
>>> +    if (url_is_streamed(s->pb)) {
>>> +        if (stream_index<  0) {
>>> +            AVStream *st;
>>> +
>>> +            stream_index = av_find_default_stream_index(s);
>>> +            if (stream_index<  0)
>>> +                return -1;
>>> +
>>> +            st = s->streams[stream_index];
>>> +            // timestamp for default must be expressed in AV_TIME_BASE 
>>> units
>>> +            ts = av_rescale(ts, st->time_base.den,
>>> +                                AV_TIME_BASE * 
>>> (int64_t)st->time_base.num);
>>> +        }
>>> +        ret = av_url_read_fseek(s->pb, stream_index, ts, flags);
>>> +    }
>>> +
>>> +    if (ret == AVERROR_NOTSUPP)
>>> +        ret = av_seek_frame(s, stream_index, ts, flags | (ts - min_ts>  
>>> (uint64_t)(max_ts - ts) ? AVSEEK_FLAG_BACKWARD : 0));
>>> +    return ret;
>>> +}
>>
>> now i see what you meant by that this will need to be changed again
>> either way this does not implement the new API correctly
>
> It's simply based on the behavior of avformat_seek_file(). I just aimed at 
> producing the same result for non-streams, while giving the protocol 
> handler read_seek a chance to run.

the behavior of above in case av_url_read_fseek() is used seems to
differ quite a bit from what the new api docs expect


>
>> also you mix AVERROR_NOTSUPP with AVERROR(ENOSYS)
>
> They are identical. AVERROR_NOTSUPP is defined to AVERROR(ENOSYS) in 
> libavutil/error.h.

currently yes, and maybe always so but i prefer code that does not
depend on such assumtations

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

No human being will ever know the Truth, for even if they happen to say it
by chance, they would not even known they had done so. -- Xenophanes
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