[Libav-user] re-encoding and transcode (codec copy) on same file.

[YIRAN LI]

2017-04-12 0:55 GMT+10:00 Andy Shaules <bowljoman at gmail.com>:

> On 4/10/2017 4:37 PM, YIRAN LI wrote:
>
>
>
> 2017-04-10 7:16 GMT+10:00 bowljoman <bowljoman at gmail.com>:
>
>>
>> sorry if this client top posts, but to answer, you can do 1 of 2 things.
>> assume it is different and insert it before returning to the unprocessed
>> clip. or you can check if they are different by doing a comparison.
>>
>>
>> ​Thanks for your suggestion. Let's say if original H.264 video stream has
> AVCC bitstream, no matter you encode 1st part with Annex-b or AVCC, as long
> as it's different from orginal format, I won't be able to do codec copy
> using readpacket/writepacket, right?
>
> Thanks
> ​
>
>> Sent from my T-Mobile 4G LTE Device
>>
>> -------- Original message --------
>> From: YIRAN LI <mrfun.china at gmail.com>
>> Date: 4/7/17 3:15 PM (GMT-08:00)
>> To: "This list is about using libavcodec, libavformat, libavutil,
>> libavdevice and libavfilter." <libav-user at ffmpeg.org>, FFmpeg user
>> questions <ffmpeg-user at ffmpeg.org>
>> Subject: [Libav-user] re-encoding and transcode (codec copy) on same
>> file.
>>
>> Hi guys,
>>
>> I'm investigating if it's possible to do editing and transcode on same
>> file.
>>
>> I mean use -vcodec copy, we can readout packets and write them directly
>> into output file without re-encoding. But if it's possible, for example if
>> I have a 2 mins video, re-encode 1st min because there're some effects
>> applied to that region but copy 2nd part?
>>
>> My concern is, for example we know H.264 has extradata, if I re-encode
>> first part but keep 2nd part, how if new extradata is different from old
>> extradta?
>>
>> Anyone have suggestion on this? and any other possible problems doing
>> this?
>>
>> Thanks
>>
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>
>
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> It doesnt matter what the inputs are. just convert them to one or the
> other type. the final stream can be assembled with all avc or avcc packets.
> choose one or the other.
>

​Thanks for reply.

I did some research yesterday and I think no matter packets in the file is
in starting code (annex-b) or size​ (avcc) mode, I can always detect and
convert it to another mode.

The problem is, if I re-encode a part and keep another part, how can I
guarantee the SPS/PPS values for 2 parts are same? If they are different,
even if they are in packets (in-band) instead of in global header, is such
a file standard compliant ?

Thanks

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