[FFmpeg-devel] [PATCH v2] avformat/movenc : Don't write sidx for empty urls

Jeyapal, Karthick kjeyapal at akamai.com
Fri Nov 30 07:52:35 EET 2018

On 11/29/18 11:08 PM, Michael Niedermayer wrote:
> On Wed, Nov 28, 2018 at 09:45:24PM +0530, Karthick J wrote:
>> When movenc is used by other segmenting muxers such as dashenc, url field is always empty.
>> In such cases it is better to not write sidx, instead of throwing errors.
>> ---
>>  libavformat/movenc.c | 3 +++
>>  1 file changed, 3 insertions(+)
> please correct me if i misunderstand but
> dashenc enables global sidx, skiping writing the sidx then always seems a bit
> odd
Your understanding is correct. 
But the motive of dashenc is to disable writing of sidx atom for every moof atom (Let's call this as local sidx for the sake of discussion).
We wanted to disable local sidx as it was adding significant bitrate overhead for chunked streaming(where each frame is a moof).
To disable local sidx we enabled global sidx. And global sidx was not writing any sidx at all from dashenc due to lack of url. 
This behavior of not writing any sidx at all is also acceptable for dash. But we just wanted to remove the error, and hence this patch.
Maybe one could add a new option no_sidx in movenc for this functionality. But since global_sidx was already achieving the same functionality new option seemed a bit redundant.
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