[FFmpeg-devel] [PATCH 0/3] Patch set to delay output live stream

[Marton Balint]

On Tue, 5 May 2020, Tao Zhang wrote:

> Marton Balint <cus at passwd.hu> 于2020年5月5日周二 上午3:48写道：
>>
>>
>>
>> On Sat, 2 May 2020, Tao Zhang wrote:
>>
>> > Marton Balint <cus at passwd.hu> 于2020年5月2日周六 下午7:05写道：
>>
>> [...]
>>
>> >> I see. But you could add an option to the fifo muxer to only write header
>> >> when the first packet arrives. This way you will be able to use a
>> >> bitstream filter to buffer packets and the fifo muxer will only write
>> >> header when the first packet passes through the bitstream filter. Does
>> >> this seem OK?
>> > It seems OK. If nobody object it, I'm glad to add
>> > write_header_on_first_packet option on fifo muxer and create a new
>> > bitstream filter which buffers fixed duration packets.
>>
>> Great. I suggest a shorter name for the option of the fifo muxer,
>> delay_write_header I think is enough, you can explain the details in the
>> docs.
> Great suggestion. I'll follow it.
>>
>> Also it should be pretty straightforward to add this feature to fifo.c,
>> from a quick look at the code one approach is to add a NOOP message type,
>> and if the option is set, then use that message type for the first
>> message, if it is not set, use the WRITE_HEADER message type, as it is
>> used now.
>>
>> Also we should find a good name for the bitstream filter, maybe "buffer",
>> or "fifo", or if you want to better refer to the use case, then
>> "timeshift" can also work.
> Maybe "caching" or "cache"?
>>
>> Another thing you should think about is what should happen at the end of
>> the stream, when flushing the bitstream filter:
>> - drop pending packets
>> - flush pending packets as fast as possible
>> - flush pendning packets realtime
>> Maybe it should be selectable between the 3 options? I can imagine use
>> cases for all three possibilities.
> Although I have not imagined the first and second use cases, I'm glad
> to implement all three.

I have given the bitstream filter approach some additional thought and 
since each stream will have a different bitstream filter I think you will 
have problems when flushing them in ffmpeg.c because it will flush them 
sequentially, the packet interleaving will be something like
- all remaining packets from the first stream
- all remaining packets from the second stream
... etc.

Which will cause issues at muxing the last part of the stream if the 
buffer duration is larger than a few seconds.

Sorry, it looks like hacking the whole thing into fifo.c works the best 
after all. The only problem is that I don't see a clean way of doing that 
if you only want to enforce realtiem output there when flushing the 
buffered packets...

Regards,
Marton