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mp4_clipper: align start offset to keyframe
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when vod_align_segments_to_key_frames is enabled, return the video
starting from the key frame preceeding the requested clipFrom offset,
and include an editlist in the returned mp4 to instruct the player to
remove the prefix.
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@erankor
erankor committed Aug 10, 2024
1 parent 26f0687 commit 5900ee9
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Showing 3 changed files with 148 additions and 1 deletion.
8 changes: 8 additions & 0 deletions ngx_http_vod_module.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1539,6 +1539,14 @@ ngx_http_vod_init_parse_params_metadata(
parse_params->parse_type |= ctx->submodule_context.conf->parse_flags;
parse_params->codecs_mask = request->codecs_mask;
}
else
{
parse_params->parse_type = 0;
if (ctx->submodule_context.conf->segmenter.align_to_key_frames)
{
parse_params->parse_type |= PARSE_FLAG_ALIGN_TO_KEYFRAME;
}
}

request_tracks_mask = ctx->submodule_context.request_params.tracks_mask;
if (ctx->submodule_context.request_params.sequence_tracks_mask != NULL)
Expand Down
2 changes: 2 additions & 0 deletions vod/media_format.h
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Original file line number Diff line number Diff line change
Expand Up @@ -65,6 +65,8 @@
#define PARSE_FLAG_INITIAL_PTS_DELAY (0x01000000)
#define PARSE_FLAG_KEY_FRAME_BITRATE (0x02000000)

#define PARSE_FLAG_ALIGN_TO_KEYFRAME (0x10000000)

// flag groups
#define PARSE_FLAG_FRAMES_ALL (PARSE_FLAG_FRAMES_DURATION | PARSE_FLAG_FRAMES_PTS_DELAY | PARSE_FLAG_FRAMES_SIZE | PARSE_FLAG_FRAMES_OFFSET | PARSE_FLAG_FRAMES_IS_KEY)
#define PARSE_FLAG_FRAMES_ALL_EXCEPT_OFFSETS (PARSE_FLAG_FRAMES_DURATION | PARSE_FLAG_FRAMES_PTS_DELAY | PARSE_FLAG_FRAMES_SIZE | PARSE_FLAG_FRAMES_IS_KEY)
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139 changes: 138 additions & 1 deletion vod/mp4/mp4_clipper.c
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Original file line number Diff line number Diff line change
Expand Up @@ -93,6 +93,7 @@ enum {
MP4_CLIPPER_TRAK_INDEX_STSZ_DATA,
MP4_CLIPPER_TRAK_INDEX_STCO_HEADER,
MP4_CLIPPER_TRAK_INDEX_STCO_DATA,
MP4_CLIPPER_TRAK_INDEX_EDTS_ATOM,

MP4_CLIPPER_TRAK_INDEX_COUNT
};
Expand Down Expand Up @@ -126,6 +127,7 @@ typedef struct {
size_t data_size;
size_t atom_size;
uint32_t entries;
uint64_t prefix;
} stts_clip_result_t;

typedef struct {
Expand Down Expand Up @@ -197,6 +199,7 @@ typedef struct {
size_t stbl_atom_size;
size_t minf_atom_size;
size_t mdia_atom_size;
size_t edts_atom_size;
size_t trak_atom_size;
} parsed_trak_t;

Expand Down Expand Up @@ -530,10 +533,91 @@ mp4_clipper_mdhd_update_atom(u_char* p, mdhd_clip_result_t* mdhd)
}

// stts
static vod_status_t
mp4_clipper_stts_seek_to_keyframe(
parse_trak_atom_context_t* context,
stts_iterator_state_t* iterator,
atom_info_t* stss_atom,
uint64_t* prefix)
{
vod_status_t rc;
uint32_t* first_entry;
uint32_t* entry;
uint64_t initial_duration;
uint32_t sample_duration;
uint32_t sample_count;
uint32_t entry_index;
uint32_t key_index;
uint32_t entries;
uint32_t count;
uint32_t left;

if (stss_atom->size <= 0)
{
return VOD_OK;
}

rc = mp4_parser_validate_stss_atom(context->request_context, stss_atom, &entries);
if (rc != VOD_OK)
{
return rc;
}

if (entries <= 0)
{
vod_log_error(VOD_LOG_ERR, context->request_context->log, 0,
"mp4_clipper_stts_seek_to_keyframe: zero entries");
return VOD_BAD_DATA;
}

// first the last key frame before iterator->frame_index
first_entry = (uint32_t*)(stss_atom->ptr + sizeof(stss_atom_t));
entry_index = mp4_parser_find_stss_entry(iterator->frame_index, first_entry, entries);
entry = first_entry + entry_index;
if (entry_index > 0 && (entry_index >= entries || parse_be32(entry) > iterator->frame_index + 1))
{
entry--;
}

key_index = parse_be32(entry) - 1;

// seek back to key_index
initial_duration = iterator->accum_duration;
sample_count = parse_be32(iterator->cur_entry->count);
while (iterator->frame_index > key_index)
{
if (iterator->sample_count >= sample_count)
{
iterator->cur_entry--;
iterator->sample_count = 0;
sample_count = parse_be32(iterator->cur_entry->count);
continue;
}

count = sample_count - iterator->sample_count;
left = iterator->frame_index - key_index;
if (count > left)
{
count = left;
}

sample_duration = parse_be32(iterator->cur_entry->duration);

iterator->sample_count += count;
iterator->frame_index -= count;
iterator->accum_duration -= count * sample_duration;
}

*prefix = initial_duration - iterator->accum_duration;

return VOD_OK;
}

static vod_status_t
mp4_clipper_stts_clip_data(
parse_trak_atom_context_t* context,
atom_info_t* atom_info,
atom_info_t* stss_atom,
stts_clip_result_t* result,
uint32_t* first_frame,
uint32_t* last_frame)
Expand Down Expand Up @@ -574,6 +658,15 @@ mp4_clipper_stts_clip_data(
"mp4_clipper_stts_clip_data: clip from longer than video duration");
return VOD_BAD_REQUEST;
}

if (context->parse_params.parse_type & PARSE_FLAG_ALIGN_TO_KEYFRAME)
{
rc = mp4_clipper_stts_seek_to_keyframe(context, &iterator, stss_atom, &result->prefix);
if (rc != VOD_OK)
{
return rc;
}
}
}

result->first_entry = iterator.cur_entry;
Expand All @@ -584,7 +677,8 @@ mp4_clipper_stts_clip_data(
{
// Note: the below was done to match nginx mp4, may be better to do
// clip_to = (((uint64_t)context->parse_params.clip_to * context->timescale) / 1000);
clip_to = iterator.accum_duration + (((uint64_t)(context->parse_params.clip_to - context->parse_params.clip_from) * context->timescale) / 1000);
clip_to = iterator.accum_duration + result->prefix +
(((uint64_t)(context->parse_params.clip_to - context->parse_params.clip_from) * context->timescale) / 1000);
}
else
{
Expand Down Expand Up @@ -1538,6 +1632,7 @@ mp4_clipper_process_moov_atom_callback(void* ctx, atom_info_t* atom_info)
rc = mp4_clipper_stts_clip_data(
&parse_context,
&parsed_trak->atoms[TRAK_ATOM_STTS],
&parsed_trak->atoms[TRAK_ATOM_STSS],
&parsed_trak->stts,
&parse_context.first_frame,
&parse_context.last_frame);
Expand All @@ -1546,6 +1641,8 @@ mp4_clipper_process_moov_atom_callback(void* ctx, atom_info_t* atom_info)
return rc;
}

parsed_trak->mdhd.duration += parsed_trak->stts.prefix;

if (parse_context.first_frame >= parse_context.last_frame)
{
return VOD_OK;
Expand Down Expand Up @@ -1628,8 +1725,15 @@ mp4_clipper_process_moov_atom_callback(void* ctx, atom_info_t* atom_info)
full_atom_size(parsed_trak->atoms[TRAK_ATOM_HDLR]) +
parsed_trak->minf_atom_size;

if (parsed_trak->stts.prefix > 0)
{
parsed_trak->edts_atom_size = 2 * ATOM_HEADER_SIZE + sizeof(elst_atom_t) + sizeof(elst64_entry_t);
context->result.alloc_size += parsed_trak->edts_atom_size;
}

parsed_trak->trak_atom_size = ATOM_HEADER_SIZE +
full_atom_size(parsed_trak->atoms[TRAK_ATOM_TKHD]) +
parsed_trak->edts_atom_size +
parsed_trak->mdia_atom_size;

context->result.moov_atom_size += parsed_trak->trak_atom_size;
Expand All @@ -1649,6 +1753,26 @@ mp4_clipper_process_moov_atom_callback(void* ctx, atom_info_t* atom_info)
return VOD_OK;
}

static u_char*
mp4_clipper_edts_write_atom(u_char* p, parsed_trak_t* parsed_trak)
{
size_t elst_atom_size;

elst_atom_size = parsed_trak->edts_atom_size - ATOM_HEADER_SIZE;

write_atom_header(p, parsed_trak->edts_atom_size, 'e', 'd', 't', 's');
write_atom_header(p, elst_atom_size, 'e', 'l', 's', 't');

write_be32(p, 1 << 24); // version = 1
write_be32(p, 1); // entries
write_be64(p, parsed_trak->tkhd.duration);
write_be64(p, parsed_trak->stts.prefix);
write_be16(p, 1); // media_rate
write_be16(p, 0); // reserved

return p;
}

static u_char*
mp4_clipper_trak_write_atom(u_char* p, void* write_context, parsed_trak_t* parsed_trak, bool_t copy_data, int64_t chunk_pos_diff)
{
Expand All @@ -1657,6 +1781,12 @@ mp4_clipper_trak_write_atom(u_char* p, void* write_context, parsed_trak_t* parse
write_atom_header(p, parsed_trak->trak_atom_size, 't', 'r', 'a', 'k');
copy_full_atom(p, parsed_trak->atoms[TRAK_ATOM_TKHD]);
mp4_clipper_tkhd_update_atom(p - parsed_trak->atoms[TRAK_ATOM_TKHD].size, &parsed_trak->tkhd);

if (parsed_trak->edts_atom_size > 0)
{
p = mp4_clipper_edts_write_atom(p, parsed_trak);
}

write_atom_header(p, parsed_trak->mdia_atom_size, 'm', 'd', 'i', 'a');
copy_full_atom(p, parsed_trak->atoms[TRAK_ATOM_MDHD]);
mp4_clipper_mdhd_update_atom(p - parsed_trak->atoms[TRAK_ATOM_MDHD].size, &parsed_trak->mdhd);
Expand All @@ -1678,6 +1808,13 @@ mp4_clipper_trak_write_atom(u_char* p, void* write_context, parsed_trak_t* parse
mp4_clipper_tkhd_update_atom((u_char*)parsed_trak->atoms[TRAK_ATOM_TKHD].ptr, &parsed_trak->tkhd);
write_full_atom(write_context, MP4_CLIPPER_TRAK_INDEX_TKHD_ATOM, parsed_trak->atoms[TRAK_ATOM_TKHD]);

if (parsed_trak->edts_atom_size > 0)
{
// trak.edts
p = mp4_clipper_edts_write_atom(p, parsed_trak);
mp4_clipper_write_tail(write_context, MP4_CLIPPER_TRAK_INDEX_EDTS_ATOM, p - parsed_trak->edts_atom_size, parsed_trak->edts_atom_size);
}

// trak.mdia
write_atom_header(p, parsed_trak->mdia_atom_size, 'm', 'd', 'i', 'a');
mp4_clipper_write_tail(write_context, MP4_CLIPPER_TRAK_INDEX_MDIA_HEADER, p - ATOM_HEADER_SIZE, ATOM_HEADER_SIZE);
Expand Down

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