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avcodec/decode: Avoid stack packets when decoding subtitles

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Use AVCodecInternal.buffer_pkt (previously only used in
avcodec_send_packet) instead of stack packets when decoding subtitles.
Also stop sharing side-data between packets and use the user-supplied
packet directly for decoding when possible (no subtitle decoder ever
modifies the packet it is given).
Reusing AVCodecInternal.buffer_pkt is based upon an idea from James
Almer.

Reviewed-by: James Almer <jamrial@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
This commit is contained in:
Andreas Rheinhardt 2021-03-04 10:53:26 +01:00
parent f0dc8faeb1
commit e12923f683
1 changed files with 29 additions and 28 deletions
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57
libavcodec/decode.c
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@ -869,19 +869,20 @@ static void get_subtitle_defaults(AVSubtitle *sub)
}
#define UTF8_MAX_BYTES 4 /* 5 and 6 bytes sequences should not be used */
static int recode_subtitle(AVCodecContext *avctx,
AVPacket *outpkt, const AVPacket *inpkt)
static int recode_subtitle(AVCodecContext *avctx, AVPacket **outpkt,
AVPacket *inpkt, AVPacket *buf_pkt)
{
#if CONFIG_ICONV
iconv_t cd = (iconv_t)-1;
int ret = 0;
char *inb, *outb;
size_t inl, outl;
AVPacket tmp;
#endif
if (avctx->sub_charenc_mode != FF_SUB_CHARENC_MODE_PRE_DECODER || inpkt->size == 0)
if (avctx->sub_charenc_mode != FF_SUB_CHARENC_MODE_PRE_DECODER || inpkt->size == 0) {
*outpkt = inpkt;
return 0;
}
#if CONFIG_ICONV
inb = inpkt->data;
@ -895,28 +896,31 @@ static int recode_subtitle(AVCodecContext *avctx,
cd = iconv_open("UTF-8", avctx->sub_charenc);
av_assert0(cd != (iconv_t)-1);
ret = av_new_packet(&tmp, inl * UTF8_MAX_BYTES);
ret = av_new_packet(buf_pkt, inl * UTF8_MAX_BYTES);
if (ret < 0)
goto end;
outpkt->buf = tmp.buf;
outpkt->data = tmp.data;
outpkt->size = tmp.size;
outb = outpkt->data;
outl = outpkt->size;
ret = av_packet_copy_props(buf_pkt, inpkt);
if (ret < 0)
goto end;
outb = buf_pkt->data;
outl = buf_pkt->size;
if (iconv(cd, &inb, &inl, &outb, &outl) == (size_t)-1 ||
iconv(cd, NULL, NULL, &outb, &outl) == (size_t)-1 ||
outl >= outpkt->size || inl != 0) {
outl >= buf_pkt->size || inl != 0) {
ret = FFMIN(AVERROR(errno), -1);
av_log(avctx, AV_LOG_ERROR, "Unable to recode subtitle event \"%s\" "
"from %s to UTF-8\n", inpkt->data, avctx->sub_charenc);
av_packet_unref(&tmp);
goto end;
}
outpkt->size -= outl;
memset(outpkt->data + outpkt->size, 0, outl);
buf_pkt->size -= outl;
memset(buf_pkt->data + buf_pkt->size, 0, outl);
*outpkt = buf_pkt;
ret = 0;
end:
if (ret < 0)
av_packet_unref(buf_pkt);
if (cd != (iconv_t)-1)
iconv_close(cd);
return ret;
@ -1039,20 +1043,21 @@ int avcodec_decode_subtitle2(AVCodecContext *avctx, AVSubtitle *sub,
get_subtitle_defaults(sub);
if ((avctx->codec->capabilities & AV_CODEC_CAP_DELAY) || avpkt->size) {
AVPacket pkt_recoded = *avpkt;
AVCodecInternal *avci = avctx->internal;
AVPacket *pkt;
ret = recode_subtitle(avctx, &pkt_recoded, avpkt);
ret = recode_subtitle(avctx, &pkt, avpkt, avci->buffer_pkt);
if (ret < 0)
return ret;
ret = extract_packet_props(avctx->internal, &pkt_recoded);
if (ret < 0)
return ret;
ret = extract_packet_props(avctx->internal, pkt);
if (ret < 0)
goto cleanup;
if (avctx->pkt_timebase.num && avpkt->pts != AV_NOPTS_VALUE)
sub->pts = av_rescale_q(avpkt->pts,
avctx->pkt_timebase, AV_TIME_BASE_Q);
ret = avctx->codec->decode(avctx, sub, got_sub_ptr, &pkt_recoded);
ret = avctx->codec->decode(avctx, sub, got_sub_ptr, pkt);
av_assert1((ret >= 0) >= !!*got_sub_ptr &&
!!*got_sub_ptr >= !!sub->num_rects);
@ -1091,16 +1096,12 @@ int avcodec_decode_subtitle2(AVCodecContext *avctx, AVSubtitle *sub,
}
}
if (avpkt->data != pkt_recoded.data) { // did we recode?
/* prevent from destroying side data from original packet */
pkt_recoded.side_data = NULL;
pkt_recoded.side_data_elems = 0;
av_packet_unref(&pkt_recoded);
}
if (*got_sub_ptr)
avctx->frame_number++;
cleanup:
if (pkt == avci->buffer_pkt) // did we recode?
av_packet_unref(avci->buffer_pkt);
}
return ret;