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avcodec/mmaldec: use decoupled dataflow 

MMAL is an fundamentally an asynchronous decoder, which was a bad fit
for the legacy dataflow API. Often multiple packets are enqueued before
a flood of frames are returned from MMAL.

The previous lockstep dataflow meant that any delay in returning packets
from the VPU would cause ctx->queue_decoded_frames to grow with no way
of draining the queue.

Testing this with mpv streaming from a live RTSP source visibly reduced
latency introduced by frames waiting in queue_decoded_frames from
roughly 2s to 0.

Tested-by: Cameron Gutman <aicommander@gmail.com>
Signed-off-by: Ho Ming Shun <cyph1984@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Ho Ming Shun 2021-09-24 17:04:35 +08:00 committed by Andreas Rheinhardt
parent 996b13fac4
commit b54377b3a7
1 changed files with 25 additions and 7 deletions
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28
libavcodec/mmaldec.c
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@ -83,6 +83,8 @@ typedef struct MMALDecodeContext {
// libavcodec API can't return new frames, and we have a logical deadlock.
// This is avoided by queuing such buffers here.
FFBufferEntry *waiting_buffers, *waiting_buffers_tail;
/* Packet used to hold received packets temporarily; not owned by us. */
AVPacket *pkt;
int64_t packets_sent;
atomic_int packets_buffered;
@ -355,6 +357,8 @@ static av_cold int ffmmal_init_decoder(AVCodecContext *avctx)
MMAL_COMPONENT_T *decoder;
int ret = 0;
ctx->pkt = avctx->internal->in_pkt;
bcm_host_init();
if (mmal_vc_init()) {
@ -570,6 +574,7 @@ static int ffmmal_add_packet(AVCodecContext *avctx, AVPacket *avpkt,
done:
av_buffer_unref(&buf);
av_packet_unref(avpkt);
return ret;
}
@ -655,6 +660,12 @@ static int ffmal_copy_frame(AVCodecContext *avctx, AVFrame *frame,
avctx->pix_fmt, avctx->width, avctx->height);
}
frame->sample_aspect_ratio = avctx->sample_aspect_ratio;
frame->width = avctx->width;
frame->width = avctx->width;
frame->height = avctx->height;
frame->format = avctx->pix_fmt;
frame->pts = buffer->pts == MMAL_TIME_UNKNOWN ? AV_NOPTS_VALUE : buffer->pts;
frame->pkt_dts = AV_NOPTS_VALUE;
@ -763,12 +774,12 @@ done:
return ret;
}
static int ffmmal_decode(AVCodecContext *avctx, void *data, int *got_frame,
AVPacket *avpkt)
static int ffmmal_receive_frame(AVCodecContext *avctx, AVFrame *frame)
{
MMALDecodeContext *ctx = avctx->priv_data;
AVFrame *frame = data;
AVPacket *const avpkt = ctx->pkt;
int ret = 0;
int got_frame = 0;
if (avctx->extradata_size && !ctx->extradata_sent) {
AVPacket pkt = {0};
@ -780,8 +791,12 @@ static int ffmmal_decode(AVCodecContext *avctx, void *data, int *got_frame,
return ret;
}
ret = ff_decode_get_packet(avctx, avpkt);
if (ret == 0) {
if ((ret = ffmmal_add_packet(avctx, avpkt, 0)) < 0)
return ret;
} else if (ret < 0 && !(ret == AVERROR(EAGAIN)))
return ret;
if ((ret = ffmmal_fill_input_port(avctx)) < 0)
return ret;
@ -789,7 +804,7 @@ static int ffmmal_decode(AVCodecContext *avctx, void *data, int *got_frame,
if ((ret = ffmmal_fill_output_port(avctx)) < 0)
return ret;
if ((ret = ffmmal_read_frame(avctx, frame, got_frame)) < 0)
if ((ret = ffmmal_read_frame(avctx, frame, &got_frame)) < 0)
return ret;
// ffmmal_read_frame() can block for a while. Since the decoder is
@ -801,6 +816,9 @@ static int ffmmal_decode(AVCodecContext *avctx, void *data, int *got_frame,
if ((ret = ffmmal_fill_input_port(avctx)) < 0)
return ret;
if (!got_frame && ret == 0)
return AVERROR(EAGAIN);
else
return ret;
}
@ -833,7 +851,7 @@ static const AVOption options[]={
.priv_data_size = sizeof(MMALDecodeContext), \
.init = ffmmal_init_decoder, \
.close = ffmmal_close_decoder, \
.decode = ffmmal_decode, \
.receive_frame = ffmmal_receive_frame, \
.flush = ffmmal_flush, \
.priv_class = &ffmmal_##NAME##_dec_class, \
.capabilities = AV_CODEC_CAP_DELAY | AV_CODEC_CAP_HARDWARE, \