[Libav-user] Add subtitles to MKV file

[wm4]

On Sat, 5 Jul 2014 16:15:44 +0800
"ingmar" <ingmar at kingsoftware.com.tw> wrote:

> Hello Everyone!
> 
>  
> 
> I am trying to add some text, being a stream, into an MKV file which has
> encoded video and audio data already. Because of some reasons, storing the
> text to an isolated file is not acceptable.
> 
>  
> 
> The problem I encountered was the times of subtitles were incorrect like
> below.
> 
>  
> 
> [Original]
> 
> 1
> 
> 00:00:00,000 --> 00:00:00,999
> 
> 2014-07-01 11:59:28
> 
>  
> 
> 2
> 
> 00:00:01,000 --> 00:00:01,999
> 
> 2014-07-01 11:59:29
> 
>  
> 
> [Encoded]
> 
> 1
> 
> 00:02:11,072 --> 00:02:12,071
> 
> 2014-07-01 11:59:28
> 
>  
> 
> 2
> 
> 00:02:12,072 --> 00:02:13,071
> 
> 2014-07-01 11:59:29
> 
>  
> 
> My approach is following.
> 
> 1. Create 3 streams: video, audio and subtitle with code AV_CODEC_ID_SUBRIP
> and add to the target MKV file.
> 
> 2. Encode all video and audio data.
> 
> 3. Create a temporary SRT file and store all text in it.
> 
> 4. Read a packet from SRT file (av_read_frame) -> decode
> (avcodec_decode_subtitle2) -> encode (avcodec_encode_subtitle) -> write to
> MKV file (av_interleaved_write_frame).
> 
>  
> 
> I have been sure the time_base fields of the input and output streams were
> the same; and also for the pts, dts and duration ones of the input and
> output packets.
> 
>  
> 
> Any advice would be greatly appreciated.
> 

Maybe wrong timebase in timestamp calculations? Just guessing.