On 6/7/2023 1:30 PM, Dawid Kozinski/Multimedia (PLT) /SRPOL/Staff
Engineer/Samsung Electronics wrote:
-----Original Message-----
From: Dawid Kozinski/Multimedia (PLT) /SRPOL/Staff Engineer/Samsung
Electronics <d.kozin...@samsung.com>
Sent: środa, 7 czerwca 2023 17:41
To: 'FFmpeg development discussions and patches' <ffmpeg-
de...@ffmpeg.org>
Subject: RE: [FFmpeg-devel] [PATCH v23 04/10] avformat/evc_demuxer: Added
demuxer to handle reading EVC video files
-----Original Message-----
From: ffmpeg-devel <ffmpeg-devel-boun...@ffmpeg.org> On Behalf Of
James Almer
Sent: środa, 7 czerwca 2023 15:40
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH v23 04/10] avformat/evc_demuxer:
Added demuxer to handle reading EVC video files
On 6/7/2023 10:36 AM, Dawid Kozinski/Multimedia (PLT) /SRPOL/Staff
Engineer/Samsung Electronics wrote:
-----Original Message-----
From: ffmpeg-devel <ffmpeg-devel-boun...@ffmpeg.org> On Behalf Of
James Almer
Sent: poniedziałek, 29 maja 2023 15:08
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH v23 04/10] avformat/evc_demuxer:
Added demuxer to handle reading EVC video files
On 5/26/2023 7:31 AM, Dawid Kozinski wrote:
+static int get_temporal_id(const uint8_t *bits, int bits_size) {
+ int temporal_id = 0;
+ short t = 0;
+
+ if (bits_size >= EVC_NALU_HEADER_SIZE) {
+ unsigned char *p = (unsigned char *)bits;
+ // forbidden_zero_bit
+ if ((p[0] & 0x80) != 0)
+ return -1;
+
+ for (int i = 0; i < EVC_NALU_HEADER_SIZE; i++)
+ t = (t << 8) | p[i];
I think this can be replaced with AV_RB16.
+
+ temporal_id = (t >> 6) & 0x0007;
+ }
+
+ return temporal_id;
+}
[...]
+static uint32_t read_nal_unit_length(const uint8_t *bits, int
+bits_size) {
+ uint32_t nalu_len = 0;
+
+ if (bits_size >= EVC_NALU_LENGTH_PREFIX_SIZE) {
+
+ int t = 0;
+ unsigned char *p = (unsigned char *)bits;
+
+ for (int i = 0; i < EVC_NALU_LENGTH_PREFIX_SIZE; i++)
+ t = (t << 8) | p[i];
AV_RB32.
+
+ nalu_len = t;
+ if (nalu_len == 0) // Invalid bitstream size
+ return 0;
+ }
+
+ return nalu_len;
+}
[...]
+static int evc_frame_merge_filter(AVBSFContext *bsf, AVPacket *out) {
+ EVCMergeContext *ctx = bsf->priv_data;
+ AVPacket *in = ctx->in;
+
+ int free_space = 0;
+ size_t nalu_size = 0;
+ uint8_t *nalu = NULL;
+ int au_end_found = 0;
+ int err;
+
+ err = ff_bsf_get_packet_ref(bsf, in);
+ if (err < 0)
+ return err;
+
+ nalu_size = read_nal_unit_length(in->data,
EVC_NALU_LENGTH_PREFIX_SIZE);
+ if(nalu_size <= 0) {
+ av_packet_unref(in);
+ return AVERROR_INVALIDDATA;
+ }
+
+ nalu = in->data + EVC_NALU_LENGTH_PREFIX_SIZE;
+ nalu_size = in->size - EVC_NALU_LENGTH_PREFIX_SIZE;
+
+ // NAL unit parsing needed to determine if end of AU was found
+ err = parse_nal_unit(nalu, nalu_size, bsf);
+ if (err < 0) {
+ av_log(bsf, AV_LOG_ERROR, "NAL Unit parsing error\n");
+ av_packet_unref(in);
+
+ return err;
+ }
+
+ au_end_found = end_of_access_unit_found(bsf);
+
+ free_space = ctx->au_buffer.capacity - ctx->au_buffer.data_size;
+ while( free_space < in->size ) {
+ ctx->au_buffer.capacity *= 2;
+ free_space = ctx->au_buffer.capacity -
+ ctx->au_buffer.data_size;
+
+ if(free_space >= in->size) {
+ ctx->au_buffer.data = av_realloc(ctx->au_buffer.data,
+ ctx-
au_buffer.capacity);
+ }
+ }
+
+ memcpy(ctx->au_buffer.data + ctx->au_buffer.data_size,
+ in->data,
+ in->size);
This is including the Annex-B's nal_unit_lenght value into the
assembled
packet. I
assume libxevd expects this? Also, is it defined as part of the
ISOBMFF encapsulation? Patch 07/10 does not seem to strip it.
Could you expand on this topic?
What do you mean by "Patch 07/10 does not seem to strip it"?
Patch 7/10 expands the implementation of the MOV Muxer to support
the EVC stream.
The function ff_isom_write_evcc parses the received data, extracts
NAL units of types SPS, PPS, APS, SEI, and inserts their contents
into the corresponding elements of the arrays array, which is a
component of the EVCDecoderConfigurationRecord structure.
Additionally, the ff_isom_write_evcc function populates the relevant
fields of the EVCDecoderConfigurationRecord structure based on the
parsed SPS NAL unit data, and then calls the evcc_write function,
which writes the EVCDecoderConfigurationRecord to the stream.
It seems that I don't understand what's wrong with our
implementation ( I mean MOV muxer for EVC) and it seems I need your
help in this matter. I need an explanation of what's wrong and what
should be done to fix
the issue.
I mean the packets that go into ISOBMFF Sample, not the evcc atom. Is
the encapsulation supposed to include the nal_unit_length from Annex-B?
The function mov_write_single_packet(s, pkt) receives packets containing the
Access Units (AU) of an EVC stream. Each AU consists of a sequence of NAL
units, each preceded by a 4-byte prefix that contains information about the
length of the NAL unit. The entire AU is then copied to AVIOContext using
avio_write(pb, pkt->data, size).
It seems to me that everything is okay. If I am mistaken, just let me know.
As we have also completed all the fixes following your review this is the last
thing blocking us from creating a new patchset.
If the 4 byte prefix goes into ISOBMFF encapsulation then, it's fine.
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