On 11/10/2018 14:08, Paul B Mahol wrote:
On 10/11/18, Jerome Martinez <jer...@mediaarea.net> wrote:
Hi,
Testing FFmpeg FFV1 encoder on big frames (more than 4K: 4300x3956), I
have a warning for each frame encoded (so a lot of warnings!):
[ffv1 @ 0000024a6bcfe880] Cannot allocate worst case packet size, the
encoding could fail
Checking avcodec/ffv1enc.c, it is due to the following lines:
int64_t maxsize = AV_INPUT_BUFFER_MIN_SIZE
+ avctx->width*avctx->height*37LL*4;
[...]
if (maxsize > INT_MAX - AV_INPUT_BUFFER_PADDING_SIZE - 32) {
av_log(avctx, AV_LOG_WARNING, "Cannot allocate worst case
packet size, the encoding could fail\n");
maxsize = INT_MAX - AV_INPUT_BUFFER_PADDING_SIZE - 32;
}
The value of maxsize is 2517614784, more than INT_MAX, sure, but I don't
understand:
- why does FFmpeg need to allocate 148 times the size of a frame?
- why is having a number > INT_MAX an issue? modern machines are 64-bit
and have 8+ GB of RAM, and in practice I currently saw no encoding
failure on thousands of frames.
Additionally I didn't get why maxsize is reduced ("only" need of 12
times the size of the frame) in case of FFV1 version > 3 (experimental
right now):
if (f->version > 3)
maxsize = AV_INPUT_BUFFER_MIN_SIZE +
avctx->width*avctx->height*3LL*4;
maxsize is used for calling ff_alloc_packet2(), which accepts 64-bit
numbers.
if ((ret = ff_alloc_packet2(avctx, pkt, maxsize, 0)) < 0)
return ret;
Is it possible to reduce this "37x4" multiplier without risk and/or
remove maxsize reduction in case of sizeof(size_t) == 8 and/or show the
warning only once?
Issue can be reproduced with:
./ffmpeg.exe -f lavfi -i testsrc2=size=4300x3956 -t 0.040 -pix_fmt
rgba64 rgba64.dpx
./ffmpeg.exe -i rgba64.dpx -c:v ffv1 rgba64.mkv
You are not using latest version of FFv1.
As far as I know, version 3 is the latest (stable) version of FFV1, and
I use this one.
version > 3 are experimental.
I am not sure that advising to use an experimental version for "fixing"
a warning is good.
Additionally, in theory a 16kx16k content would still produce this
warning with FFV1 (experimental) v4 encoding, even if there is 16
Terabytes of RAM (more than enough for having the MAX_INT = 2 GiB raw
frame in RAM), so I understand that the warning would still be there (in
theory) with FFV1 (experimental) v4.
In latest version, encoder will not produce packets which are bigger than
input ones -- uncompressed raw. And instead if that happens it will encode
as raw video.
Theoretically output packets for old versions of FFv1 could be several
times bigger than raw input frame.
In this case, the ratio (148 times the size of input) is proportional to
the input frame size, and the test is on a fixed value (MAX_INT).
I get now the reason to reserve more than the size of the input frame.
I don't get the relationship between your explanation and these hard
coded values (148 times the size of input and MAX_INT limit).
Why 148x (37x4) and not 147 or 149?
Why a warning and maxsize forced to MAX_INT if maxsize > MAX_INT? Is it
an internal constraint of FFmpeg which would be not able to store
encoded frames bigger than MAX_INT?
Can any of that be changed e.g. warning only once for avoiding "spam" of
such warning which hides other warnings during encoding?
Jérôme
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