[FFmpeg-devel] [PATCH 1/3] lavc: do not init frame with guessed layout.

[Hendrik Leppkes]

On Thu, Mar 14, 2013 at 11:33 PM, Nicolas George
<nicolas.george at normalesup.org> wrote:
> Le quartidi 24 ventôse, an CCXXI, Hendrik Leppkes a écrit :
>> I just did a quick grep, and its used in very critical parts that
>> would immediately break if you combine planar audio with unknown
>> channel layout, because its used to allocate the planar data buffers.
>>
>> If frames with unknown channel layout are supposed to be supported,
>> those cases should definitely be changed first to use
>> AVFrame->channels. The fork doesn't have have channels and relys on
>> channel_layout alone, which is why its used in all critical parts.
>> Basically, all cases where av_get_channel_layout_nb_channels is used
>> in avutil/frame.c and quite some in avfilter would be affected by
>> this.
>>
>> So, before this is the case, i'm quite sure it would cause severe
>> regressions, even if none appear in FATE.
>
> I do not think it can cause severe regressions, because they would only
> happen in cases that currently, more or less, do not work. You can not
> regress from "do now work".
>

Well look at avutil/frame.c, av_frame_get_buffer checks for the layout
and otherwise errors, and get_audio_buffer uses it to determine the
number of channels, and its used in many more places in that file to
determine the number of channels for allocation or buffer
copy.(av_frame_ref/av_frame_make_writable).
And that file is very central for how avcodec and avfilter work.

To be honest, reading this code, i'm not sure how it works with any
file with unknown layout right now, but not sure if i actually have a
file like that to check this.