[FFmpeg-devel] [PATCH] libx265: support ATSC A/53 captions

[Timo Rothenpieler]

On 08.11.2022 15:25, Eran Kornblau wrote:
>>
>> -----Original Message-----
>> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of Timo Rothenpieler
>> Sent: Tuesday, 8 November 2022 13:33
>> To: ffmpeg-devel at ffmpeg.org
>> Subject: Re: [FFmpeg-devel] [PATCH] libx265: support ATSC A/53 captions
>>
>>>
>>> The attached patch adds rendering of ATSC A/53 captions as HEVC SEI messages.
>>> The option name/implementation is aligned with the corresponding libx264 feature.
>>
>> What frees the sei data on success?
>>
> Thanks Timo, good point!
> 
> I missed the fact that libx264 gets a callback for freeing the SEI payloads (sei_free).
> It seems libx265 does not have this option, so I added some 'for' loop to free the payloads after the call to encoder_encode.
> 
> In addition:
> 1. I added av_memdup on the 'user-data-unregistered' side data so that it won't be freed twice.
> 2. I added a 'free_picture' function for freeing the x265_picture in case of error.
> (both changes are aligned with the implementation in libx264.c)
> 
> Updated patch attached.

One nit: splitting the first line of free_picture() in two isn't really 
neccesary and makes the function a bit uglier.

One small problem: libx265 now needs to select atsc_a53 in configure, 
analog to how libx264 and all the others do.
Otherwise the file containing the a53 code might not get compiled.

LGTM otherwise

> While checking the point you raised, I ran some libx265 transcode with valgrind, and it reported errors unrelated to this patch.
> Attaching the full output, in case anyone wants to have a look.

x265 has a bunch of issues related to SEI data.
See for example https://trac.ffmpeg.org/ticket/9666#comment:1

i.e. if the number of per-frame sei data ever increases past its initial 
count, it'll just straight up explode.