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fftools/ffmpeg_dec: restructure audio/video decoding loop 
It currently emulates the long-removed
avcodec_decode_audio4/avcodec_decode_video2 APIs, which obfuscates the
actual decoding flow. Restructure the decoding calls so that they
naturally follow the new avcodec_send_packet()/avcodec_receive_frame()
design.

This is not only significantly easier to read, but also shorter.
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@elenril
elenril committed May 22, 2023
1 parent 172f901 commit 748f299
Showing 1 changed file with 65 additions and 126 deletions.
191 changes: 65 additions & 126 deletions fftools/ffmpeg_dec.c
View file
Expand Up @@ -31,15 +31,15 @@

#include "ffmpeg.h"

static void check_decode_result(InputStream *ist, int *got_output, int ret)
static void check_decode_result(InputStream *ist, int got_output, int ret)
{
if (ret < 0)
ist->decode_errors++;

if (ret < 0 && exit_on_error)
exit_program(1);

if (*got_output && ist->dec_ctx->codec_type != AVMEDIA_TYPE_SUBTITLE) {
if (got_output && ist->dec_ctx->codec_type != AVMEDIA_TYPE_SUBTITLE) {
if (ist->decoded_frame->decode_error_flags || (ist->decoded_frame->flags & AV_FRAME_FLAG_CORRUPT)) {
av_log(ist, exit_on_error ? AV_LOG_FATAL : AV_LOG_WARNING,
"corrupt decoded frame\n");
Expand All @@ -49,52 +49,6 @@ static void check_decode_result(InputStream *ist, int *got_output, int ret)
}
}

// This does not quite work like avcodec_decode_audio4/avcodec_decode_video2.
// There is the following difference: if you got a frame, you must call
// it again with pkt=NULL. pkt==NULL is treated differently from pkt->size==0
// (pkt==NULL means get more output, pkt->size==0 is a flush/drain packet)
static int decode(InputStream *ist, AVCodecContext *avctx,
AVFrame *frame, int *got_frame, const AVPacket *pkt)
{
int ret;

*got_frame = 0;

if (pkt) {
ret = avcodec_send_packet(avctx, pkt);
// In particular, we don't expect AVERROR(EAGAIN), because we read all
// decoded frames with avcodec_receive_frame() until done.
if (ret < 0 && ret != AVERROR_EOF)
return ret;
}

ret = avcodec_receive_frame(avctx, frame);
if (ret < 0 && ret != AVERROR(EAGAIN))
return ret;
if (ret >= 0) {
if (ist->want_frame_data) {
FrameData *fd;

av_assert0(!frame->opaque_ref);
frame->opaque_ref = av_buffer_allocz(sizeof(*fd));
if (!frame->opaque_ref) {
av_frame_unref(frame);
return AVERROR(ENOMEM);
}
fd = (FrameData*)frame->opaque_ref->data;
fd->pts = frame->pts;
fd->tb = avctx->pkt_timebase;
fd->idx = avctx->frame_num - 1;
}

frame->time_base = avctx->pkt_timebase;

*got_frame = 1;
}

return 0;
}

static int send_frame_to_filters(InputStream *ist, AVFrame *decoded_frame)
{
int i, ret;
Expand Down Expand Up @@ -192,25 +146,10 @@ static void audio_ts_process(InputStream *ist, AVFrame *frame)
frame->time_base = tb_filter;
}

static int decode_audio(InputStream *ist, const AVPacket *pkt, int *got_output,
int *decode_failed)
static int decode_audio(InputStream *ist, AVFrame *decoded_frame)
{
AVFrame *decoded_frame = ist->decoded_frame;
AVCodecContext *avctx = ist->dec_ctx;
int ret, err = 0;

update_benchmark(NULL);
ret = decode(ist, avctx, decoded_frame, got_output, pkt);
update_benchmark("decode_audio %d.%d", ist->file_index, ist->st->index);
if (ret < 0)
*decode_failed = 1;

if (ret != AVERROR_EOF)
check_decode_result(ist, got_output, ret);

if (!*got_output || ret < 0)
return ret;

ist->samples_decoded += decoded_frame->nb_samples;
ist->frames_decoded++;

Expand Down Expand Up @@ -274,24 +213,10 @@ static int64_t video_duration_estimate(const InputStream *ist, const AVFrame *fr
return FFMAX(ist->last_frame_duration_est, 1);
}

static int decode_video(InputStream *ist, const AVPacket *pkt, int *got_output,
int eof, int *decode_failed)
static int decode_video(InputStream *ist, AVFrame *frame)
{
AVFrame *frame = ist->decoded_frame;
int ret = 0, err = 0;

// With fate-indeo3-2, we're getting 0-sized packets before EOF for some
// reason. This seems like a semi-critical bug. Don't trigger EOF, and
// skip the packet.
if (!eof && pkt && pkt->size == 0)
return 0;

update_benchmark(NULL);
ret = decode(ist, ist->dec_ctx, frame, got_output, pkt);
update_benchmark("decode_video %d.%d", ist->file_index, ist->st->index);
if (ret < 0)
*decode_failed = 1;

// The following line may be required in some cases where there is no parser
// or the parser does not has_b_frames correctly
if (ist->par->video_delay < ist->dec_ctx->has_b_frames) {
Expand All @@ -307,10 +232,6 @@ static int decode_video(InputStream *ist, const AVPacket *pkt, int *got_output,
ist->par->video_delay);
}

if (ret != AVERROR_EOF)
check_decode_result(ist, got_output, ret);

if (*got_output && ret >= 0) {
if (ist->dec_ctx->width != frame->width ||
ist->dec_ctx->height != frame->height ||
ist->dec_ctx->pix_fmt != frame->format) {
Expand All @@ -322,10 +243,6 @@ static int decode_video(InputStream *ist, const AVPacket *pkt, int *got_output,
ist->dec_ctx->height,
ist->dec_ctx->pix_fmt);
}
}

if (!*got_output || ret < 0)
return ret;

if(ist->top_field_first>=0)
frame->flags |= AV_FRAME_FLAG_TOP_FIELD_FIRST;
Expand Down Expand Up @@ -470,7 +387,7 @@ static int transcode_subtitles(InputStream *ist, const AVPacket *pkt)
exit_program(1);
}

check_decode_result(ist, &got_output, ret);
check_decode_result(ist, got_output, ret);

if (ret < 0 || !got_output) {
if (!pkt->size)
Expand Down Expand Up @@ -500,40 +417,48 @@ static int send_filter_eof(InputStream *ist)
int dec_packet(InputStream *ist, const AVPacket *pkt, int no_eof)
{
AVCodecContext *dec = ist->dec_ctx;
AVPacket *avpkt = ist->pkt;
int ret, repeating = 0;
const char *type_desc = av_get_media_type_string(dec->codec_type);
int ret;

if (dec->codec_type == AVMEDIA_TYPE_SUBTITLE)
return transcode_subtitles(ist, pkt ? pkt : ist->pkt);

if (pkt) {
av_packet_unref(avpkt);
ret = av_packet_ref(avpkt, pkt);
if (ret < 0)
return ret;
// With fate-indeo3-2, we're getting 0-sized packets before EOF for some
// reason. This seems like a semi-critical bug. Don't trigger EOF, and
// skip the packet.
if (pkt && pkt->size == 0)
return 0;

ret = avcodec_send_packet(dec, pkt);
if (ret < 0 && !(ret == AVERROR_EOF && !pkt)) {
// In particular, we don't expect AVERROR(EAGAIN), because we read all
// decoded frames with avcodec_receive_frame() until done.
av_log(ist, AV_LOG_ERROR, "Error submitting %s to decoder: %s\n",
pkt ? "packet" : "EOF", av_err2str(ret));
if (exit_on_error)
exit_program(1);

if (ret != AVERROR_EOF)
ist->decode_errors++;

return ret;
}

// while we have more to decode or while the decoder did output something on EOF
while (1) {
int got_output = 0;
int decode_failed = 0;

switch (ist->par->codec_type) {
case AVMEDIA_TYPE_AUDIO:
ret = decode_audio (ist, repeating ? NULL : avpkt, &got_output,
&decode_failed);
av_packet_unref(avpkt);
break;
case AVMEDIA_TYPE_VIDEO:
ret = decode_video (ist, repeating ? NULL : avpkt, &got_output, !pkt,
&decode_failed);
AVFrame *frame = ist->decoded_frame;

av_packet_unref(avpkt);
break;
default: av_assert0(0);
}
update_benchmark(NULL);
ret = avcodec_receive_frame(dec, frame);
update_benchmark("decode_%s %d.%d", type_desc,
ist->file_index, ist->st->index);

if (ret != AVERROR_EOF && ret != AVERROR(EAGAIN))
check_decode_result(ist, ret >= 0, ret);

if (ret == AVERROR_EOF) {
if (ret == AVERROR(EAGAIN)) {
av_assert0(pkt); // should never happen during flushing
return 0;
} else if (ret == AVERROR_EOF) {
/* after flushing, send an EOF on all the filter inputs attached to the stream */
/* except when looping we need to flush but not to send an EOF */
if (!no_eof) {
Expand All @@ -545,25 +470,39 @@ int dec_packet(InputStream *ist, const AVPacket *pkt, int no_eof)
}

return AVERROR_EOF;
} else if (ret < 0) {
av_log(ist, AV_LOG_ERROR, "Decoding error: %s\n", av_err2str(ret));
if (exit_on_error)
exit_program(1);
return ret;
}

if (ret < 0) {
if (decode_failed) {
av_log(NULL, AV_LOG_ERROR, "Error while decoding stream #%d:%d: %s\n",
ist->file_index, ist->st->index, av_err2str(ret));
} else {
av_log(NULL, AV_LOG_FATAL, "Error while processing the decoded "
"data for stream #%d:%d\n", ist->file_index, ist->st->index);
if (ist->want_frame_data) {
FrameData *fd;

av_assert0(!frame->opaque_ref);
frame->opaque_ref = av_buffer_allocz(sizeof(*fd));
if (!frame->opaque_ref) {
av_frame_unref(frame);
report_and_exit(AVERROR(ENOMEM));
}
if (!decode_failed || exit_on_error)
exit_program(1);
return ret;
fd = (FrameData*)frame->opaque_ref->data;
fd->pts = frame->pts;
fd->tb = dec->pkt_timebase;
fd->idx = dec->frame_num - 1;
}

if (!got_output)
return 0;
frame->time_base = dec->pkt_timebase;

ret = dec->codec_type == AVMEDIA_TYPE_AUDIO ?
decode_audio(ist, frame) :
decode_video(ist, frame);

repeating = 1;
if (ret < 0) {
av_log(NULL, AV_LOG_FATAL, "Error while processing the decoded "
"data for stream #%d:%d\n", ist->file_index, ist->st->index);
exit_program(1);
}
}
}

Expand Down

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