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avformat/segafilmenc: Don't store packet info in linked list
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Up until now, the Sega FILM muxer would store some information about
each packet in a linked list. When writing the trailer, the information
in said linked list would be used to write a table in the file header.
Each entry in said table is 16 bytes long, but each entry of the linked
list is 32 bytes long (assuming 64 bit pointer and no padding).
Therefore it makes sense to remove the linked list and write the array
entries directly into a dynamic buffer while writing the packet (this is
possible because the table entries don't depend on any information not
available when writing the packet (the offset is not relative to the
beginning of the file, but to the end of the table). This also
simplifies writing the array at the end (there is no need to traverse a
linked list).

Signed-off-by: Andreas Rheinhardt <[email protected]>
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@mkver
mkver committed Jul 26, 2020
1 parent 37ec33f commit 8a3329f
Showing 1 changed file with 40 additions and 89 deletions.
129 changes: 40 additions & 89 deletions libavformat/segafilmenc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -34,81 +34,21 @@
#include "internal.h"
#include "avio_internal.h"

typedef struct FILMPacket {
int audio;
int keyframe;
int32_t pts;
int32_t duration;
int32_t size;
int32_t index;
struct FILMPacket *next;
} FILMPacket;

typedef struct FILMOutputContext {
AVIOContext *header;
unsigned index;
int audio_index;
int video_index;
FILMPacket *start;
FILMPacket *last;
int64_t packet_count;
} FILMOutputContext;

static int film_write_packet_to_header(AVFormatContext *format_context, FILMPacket *pkt)
{
AVIOContext *pb = format_context->pb;
/* The bits in these two 32-bit integers contain info about the contents of this sample */
int32_t info1 = 0;
int32_t info2 = 0;

if (pkt->audio) {
/* Always the same, carries no more information than "this is audio" */
info1 = 0xFFFFFFFF;
info2 = 1;
} else {
info1 = pkt->pts;
info2 = pkt->duration;
/* The top bit being set indicates a key frame */
if (!pkt->keyframe)
info1 |= 1U << 31;
}

/* Write the 16-byte sample info packet to the STAB chunk in the header */
avio_wb32(pb, pkt->index);
avio_wb32(pb, pkt->size);
avio_wb32(pb, info1);
avio_wb32(pb, info2);

return 0;
}

static int film_write_packet(AVFormatContext *format_context, AVPacket *pkt)
{
FILMPacket *metadata;
AVIOContext *pb = format_context->pb;
FILMOutputContext *film = format_context->priv_data;
int encoded_buf_size = 0;
int encoded_buf_size, size = pkt->size;
uint32_t info1, info2;
enum AVCodecID codec_id;

/* Track the metadata used to write the header and add it to the linked list */
metadata = av_mallocz(sizeof(FILMPacket));
if (!metadata)
return AVERROR(ENOMEM);
metadata->audio = pkt->stream_index == film->audio_index;
metadata->keyframe = pkt->flags & AV_PKT_FLAG_KEY;
metadata->pts = pkt->pts;
metadata->duration = pkt->duration;
metadata->size = pkt->size;
if (film->last == NULL) {
metadata->index = 0;
} else {
metadata->index = film->last->index + film->last->size;
film->last->next = metadata;
}
metadata->next = NULL;
if (film->start == NULL)
film->start = metadata;
film->packet_count++;
film->last = metadata;

codec_id = format_context->streams[pkt->stream_index]->codecpar->codec_id;

/* Sega Cinepak has an extra two-byte header; write dummy data there,
Expand All @@ -123,7 +63,7 @@ static int film_write_packet(AVFormatContext *format_context, AVPacket *pkt)
* 8 bytes too short. However, the size in the STAB section of the header
* is correct, taking into account the extra two bytes. */
AV_WB24(&pkt->data[1], pkt->size - 8 + 2);
metadata->size += 2;
size += 2;

avio_write(pb, pkt->data, 10);
avio_wb16(pb, 0);
Expand All @@ -134,7 +74,27 @@ static int film_write_packet(AVFormatContext *format_context, AVPacket *pkt)
avio_write(pb, pkt->data, pkt->size);
}

return 0;
/* Add the 16-byte sample info entry to the dynamic buffer
* for the STAB chunk in the header */
pb = film->header;
avio_wb32(pb, film->index);
film->index += size;
avio_wb32(pb, size);
if (film->audio_index == pkt->stream_index) {
/* Always the same, carries no more information than "this is audio" */
info1 = 0xFFFFFFFF;
info2 = 1;
} else {
info1 = pkt->pts;
info2 = pkt->duration;
/* The top bit being set indicates a key frame */
if (!(pkt->flags & AV_PKT_FLAG_KEY))
info1 |= 1U << 31;
}
avio_wb32(pb, info1);
avio_wb32(pb, info2);

return pb->error;
}

static int get_audio_codec_id(enum AVCodecID codec_id)
Expand All @@ -154,11 +114,10 @@ static int get_audio_codec_id(enum AVCodecID codec_id)
static int film_init(AVFormatContext *format_context)
{
FILMOutputContext *film = format_context->priv_data;
int ret;

film->audio_index = -1;
film->video_index = -1;
film->packet_count = 0;
film->start = NULL;
film->last = NULL;

for (int i = 0; i < format_context->nb_streams; i++) {
AVStream *st = format_context->streams[i];
Expand Down Expand Up @@ -199,6 +158,8 @@ static int film_init(AVFormatContext *format_context)
av_log(format_context, AV_LOG_ERROR, "No video stream present.\n");
return AVERROR(EINVAL);
}
if ((ret = avio_open_dyn_buf(&film->header)) < 0)
return ret;

return 0;
}
Expand Down Expand Up @@ -263,15 +224,17 @@ static int shift_data(AVFormatContext *format_context, int64_t shift_size)
static int film_write_header(AVFormatContext *format_context)
{
int ret = 0;
int64_t sample_table_size, stabsize, headersize;
unsigned sample_table_size, stabsize, headersize, packet_count;
AVIOContext *pb = format_context->pb;
FILMOutputContext *film = format_context->priv_data;
FILMPacket *prev, *packet;
AVStream *video = NULL;
uint8_t *sample_table;

/* Calculate how much we need to reserve for the header;
* this is the amount the rest of the data will be shifted up by. */
sample_table_size = film->packet_count * 16;
sample_table_size = avio_get_dyn_buf(film->header, &sample_table);
packet_count = sample_table_size / 16;
sample_table_size = packet_count * 16;
stabsize = 16 + sample_table_size;
headersize = 16 + /* FILM header base */
32 + /* FDSC chunk */
Expand Down Expand Up @@ -335,7 +298,7 @@ static int film_write_header(AVFormatContext *format_context)

/* Finally, write the STAB (sample table) chunk */
ffio_wfourcc(pb, "STAB");
avio_wb32(pb, 16 + (film->packet_count * 16));
avio_wb32(pb, stabsize);
/* Framerate base frequency. Here we're assuming that the frame rate is even.
* In real world Sega FILM files, there are usually a couple of approaches:
* a) framerate base frequency is the same as the framerate, and ticks
Expand All @@ -347,31 +310,19 @@ static int film_write_header(AVFormatContext *format_context)
* are incremented by 25 for an evenly spaced framerate of 24fps. */
avio_wb32(pb, av_q2d(av_inv_q(video->time_base)));

avio_wb32(pb, film->packet_count);
avio_wb32(pb, packet_count);

/* Finally, write out each packet's data to the header */
packet = film->start;
while (packet != NULL) {
film_write_packet_to_header(format_context, packet);
prev = packet;
packet = packet->next;
av_freep(&prev);
}
film->start = film->last = NULL;
avio_write(pb, sample_table, sample_table_size);

return 0;
}

static void film_deinit(AVFormatContext *format_context)
{
FILMOutputContext *film = format_context->priv_data;
FILMPacket *packet = film->start;
while (packet != NULL) {
FILMPacket *next = packet->next;
av_free(packet);
packet = next;
}
film->start = film->last = NULL;

ffio_free_dyn_buf(&film->header);
}

AVOutputFormat ff_segafilm_muxer = {
Expand Down

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